Collimator and energy degrader for a particle therapy system

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application claims priority to, and the benefit of, <patcit id="pcit0001" dnum="US62815721"><text>U.S. Provisional Patent Application No. 62/815,721, which was filed March 8, 2019</text></patcit>, and which is titled "Delivery Of Radiation By Column". This application claims priority to, and the benefit, of <patcit id="pcit0002" dnum="US62853387"><text>U.S. Provisional Patent Application No. 62/853,387, which was filed on May 28, 2019</text></patcit>, and which is titled "Energy Degrader Including Boron Carbide". This application claims priority to, and the benefit, of <patcit id="pcit0003" dnum="US62889825"><text>U.S. Provisional Patent Application No. 62/889,825, which was filed on August 21, 2019</text></patcit>, and which is titled "Generating A Treatment Plan". This application claims priority to, and the benefit, of <patcit id="pcit0004" dnum="US62889861"><text>U.S. Provisional Patent Application No. 62/889,861, which was filed on August 21, 2019</text></patcit>, and which is titled "Collimator For A Particle Therapy System". The contents of <patcit id="pcit0005" dnum="US62815721"><text>U.S. Provisional Patent Applications Nos. 62/815,721</text></patcit>, <patcit id="pcit0006" dnum="US62853387B"><text>62/853,387</text></patcit>, <patcit id="pcit0007" dnum="US62889825B"><text>62/889,825</text></patcit>, and <patcit id="pcit0008" dnum="US62889861B"><text>62/889,861</text></patcit> are incorporated herein by reference.

TECHNICAL FIELD

0002This disclosure relates generally to a collimator and to an energy degrader for a particle therapy system.

BACKGROUND

0003Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field and are removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they move towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel.

0004A scanning system is down-beam of the extraction channel. In this example, down-beam suggests closer to an irradiation target relative to the extraction channel. The scanning system moves the particle beam relative to the irradiation target to expose various parts of the irradiation target to the particle beam. For example, to treat a tumor, the particle beam may be scanned over different parts of the tumor to expose the different parts to radiation.

0005The scanning system may include an energy degrader to change an energy of the particle beam and therefore different depths of the tumor that the particle beam impacts. A collimator may be used to trim the particle beam. For example, the collimator may allow part of the particle beam to reach the patient while preventing a different part of the particle beam from reaching the patient.

SUMMARY

0006An example system includes a particle accelerator to produce a particle beam to treat a patient and a carrier having openings including a first opening and a second opening. The carrier includes a material that inhibits transmission of the particle beam and the carrier is located between the particle accelerator and the patient. A control system is configured to control movement of the particle beam to the first opening to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first opening, and to control movement of the particle beam from the first opening to the second opening. The example system may include one or more of the following features, either alone or in combination.

0007The openings may include an array of holes, with the first opening being a first hole and the second opening being a second hole. The openings may include an array of slots, with the first opening being a first slot and the second opening being a second slot.

0008The system may include an energy degrader between the particle accelerator and the patient. The energy degrader may include structures configured to move into and out of path of the particle beam in order to change an energy of the particle beam. The control system may be configured to control movements of the structures into or out of a path of the particle beam to change the energy of the particle beam. The structures may include plates for changing the energy of the particle beam as the particle beam passes through one or more of the plates. The plates may be or include boron carbide. The particle accelerator may include a superconducting magnet having conductive coils. The control system may be configured to change a current through the conductive coils to change the energy of the particle beam.

0009The control system may be configured to change the energy of the particle beam so that the particle beam treats, through the first opening, a columnar portion of a target in the patient before the particle beam moves from the first opening to the second opening. While the particle beam is at the first opening, the particle beam may deliver a dose of radiation to the target that exceeds one Gray-per-second for a duration of less than five seconds. While the particle beam is at the first opening, the particle beam may deliver a dose of radiation to the target that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds. While the particle beam is at the first opening, the particle beam may deliver a dose of radiation to the target that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds. While the particle beam is at the first opening, the particle beam may deliver a dose of radiation to the target at any ultra-high dose rate. While the particle beam is at the first opening, the particle beam may deliver, for a duration of less than 500ms, for a duration that is between 10ms and 5s, or for a duration that is less than 5s:, a dose of radiation to the target that is greater than 100 Gray-per-second, that is greater than 200 Gray-per-second, that is greater than 300 Gray-per-second, that is greater than 400 Gray-per-second, or that is greater than 500 Gray-per-second.

0010The openings may include holes, with the first opening being a first hole and the second opening being a second hole. Controlling movement of the particle beam to the first hole and then to the second hole may include centering the particle beam at first hole then centering the particle beam at the second hole.

0011Following movement of the particle beam from the first opening to the second opening, the particle beam may never again move to the first opening.

0012The system may include a scanning magnet having conductive coils. The scanning magnet may be for generating a magnetic field to affect the movement of the particle beam. The control system may be configured to control movement of the particle beam by changing a current through the conductive coils of the scanning magnet to affect the magnetic field. The system may include a track on which the carrier is mounted for movement within a beam field of the particle beam. A motor may be configured to move the carrier along the track. The control system may be configured to control the motor to move the carrier along the track based on movement of the particle beam. The system may include a ridge filter to spread-out a Bragg peak of the particle beam.

0013The system may include a track on which the carrier is mounted for movement. A motor may be configured to move the carrier along the track in response to one or more commands from the control system. The control system may be configured to change an energy of the particle beam while the particle beam remains stationary at the second opening, and to control movement of the particle beam from the second opening to multiple additional openings, with the particle beam remaining stationary for a period of time at each of the multiple additional openings while the energy of the particle beam changes at each opening.

0014An example collimator includes a carrier having one or more openings. The carrier may be or include a material that inhibits transmission of a particle beam. Each of the one or more openings may have a size and a shape that are not changeable. Each of the one or more openings may have a size and/or a shape that are changeable. Some of the one or more openings may have a size and/or a shape that are changeable and some of the one or more openings may have a size and/or a shape that are not changeable. The collimator may include track on which the carrier is mounted for movement within a beam field of the particle beam. A motor is configured to move the carrier along the track based on movement of the particle beam. The example collimator may include one or more of the following features, either alone or in combination.

0015The one or more openings may be or include an array of holes. The one or more openings may be or include a single linear array of holes. The one or more openings may be or include one or more slots extending across a longitudinal dimension of the carrier. The one or more openings may be or include a single slot extending across a longitudinal dimension of the carrier. The carrier may be made of or include at least one of nickel, brass, or tungsten. The motor may be responsive to commands from a control system to move the carrier along the track.

0016The carrier may be a first carrier. The collimator may include a second carrier having an array of openings. The second carrier may be or include a material that inhibits transmission of a particle beam. The second carrier may be mounted for movement within the beam field of the particle beam. The motor may be configured also to move the second carrier along the track based on movement of the particle beam. The first carrier and the second carrier may be connected to each other physically. The first carrier and the second carrier may be configured for independent movement relative to each other. For example, the motor may be a first motor, and the collimator may also include a second motor configured to move the second carrier. The second motor may be configured to move the second carrier based on the movement of the particle beam.

0017An example system includes a particle accelerator to produce a particle beam to treat a patient and a carrier having an opening. The carrier may be or include a material that inhibits transmission of the particle beam. The carrier may be located between the particle accelerator and the patient. The system may include a control system to control movement of the particle beam to a first part of the opening to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first part of the opening, and to control movement of the particle beam from the first part of the opening to a second part of the opening. The example system may include one or more of the following features, either alone or in combination.

0018The opening may be or include a slot that extends along the carrier. The control system may be configured to change an energy of the particle beam while the particle beam remains stationary at the second part of the opening, and to control movement of the particle beam from the second part of the opening to multiple additional parts of the opening, with the particle beam remaining stationary for a period of time at each of the multiple additional parts of the opening while the energy of the particle beam changes at each part of the opening.

0019The control system may be configured to change the energy of the particle beam so that the particle beam treats, through the first part of the opening, a columnar portion of a target in the patient before the particle beam moves from the first part of the opening to the second part of the opening. While the particle beam is at the first part of the opening, the particle beam may deliver a dose of radiation to the target that exceeds one Gray-per-second for a duration of less than five seconds. While the particle beam is at the first part of the opening, the particle beam may deliver a dose of radiation to the target that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds. While the particle beam is at the first part of the opening, the particle beam may deliver a dose of radiation to the target that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds. While the particle beam is at the first part of the opening, the particle beam may deliver a dose of radiation to the target at an ultra-high dose rate.

0020The system may include an energy degrader between the particle accelerator and the patient. The energy degrader may include structures configured to move into and out of path of the particle beam in order to change an energy of the particle beam. The control system may be configured to control movements of the structures into or out of a path of the particle beam to change the energy of the particle beam. The structures may be or include plates for changing the energy of the particle beam as the particle beam passes through one or more plates. The one or more plates or structures may include boron carbide.

0021The particle accelerator may include a superconducting magnet comprising conductive coils. The control system may be configured to change a current through the conductive coils to change the energy of the particle beam.

0022The system may include a track on which the carrier is mounted for movement within a beam field of the particle beam. A motor may be configured to move the carrier along the track.

0023An example system includes a particle accelerator to provide a particle beam to treat a patient located in a treatment room. The system includes an energy degrader that includes multiple structures. Each structure of the multiple structures is for changing an energy of the particle beam as the particle beam passes through the structure. Each structure includes boron carbide. The system also includes actuators, each for controlling movement of a corresponding one of the multiple structures into or out of a path of the particle beam. The energy degrader is located in the treatment room. The system may include one or more of the following features, either alone or in combination.

0024Each structure may be a plate. Each structure may be a polyhedron. Each structure may be pure boron carbide. One or more of the multiple structures may include a composite material comprised of boron carbide and graphite.

0025The energy degrader may be located no more than three meters from the patient along a beamline of the particle beam. The energy degrader may be located no more than two meters from the patient along a beamline of the particle beam. The energy degrader may be located no more than one meter from the patient along a beamline of the particle beam. The system may include a scanning magnet to move the particle beam relative to the patient. The energy degrader may be located between the scanning magnet and the patient.

0026The particle beam may be applied to the patient at an ultra-high dose rate. The particle beam may be applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.

0027The structures of the energy degrader may be controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate. The actuators may be linear motors or any other appropriate type of motors.

0028An example system includes a particle accelerator to provide a particle beam to treat a patient located in a treatment room. The system includes an energy degrader that includes multiple structures. Each structure of the multiple structures is for changing an energy of the particle beam as the particle beam passes through the structure. Each structure includes boron carbide. The system also includes actuators, each for controlling movement of a corresponding one of the multiple structures into or out of a path of the particle beam. The energy degrader is located no more than four meters from the patient along a beamline of the particle beam. The system may include one or more of the following features, either alone or in combination.

0029The structures may be controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate. The energy degrader may be located no more than three meters from the patient along a beamline of the particle beam. The energy degrader may be located no more than two meters from the patient along a beamline of the particle beam. The energy degrader may be located no more than one meter from the patient along a beamline of the particle beam.

0030The particle beam may be applied to the patient at an ultra-high dose rate. The particle beam may be applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.

0031The structures of the energy degrader may be controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate. The actuators may be linear motors or other types of motors. One or more of the multiple structures may include a composite material comprised of boron carbide and graphite.

0032An example system includes a particle accelerator to provide a particle beam to treat a patient located in a treatment room, a scanning magnet to move the particle beam relative to the patient, and an energy degrader. The energy degrader includes multiple structures. Each structure of the multiple structures is for changing an energy of the particle beam as the particle beam passes through the structure. Each structure includes boron carbide. The system also includes actuators, each for controlling movement of a corresponding one of the multiple structures into or out of a path of the particle beam. The energy degrader is located between the scanning magnet and the patient. The system may include one or more of the following features, either alone or in combination.

0033The energy degrader may be located no more than one meter from the patient along a beamline of the particle beam. The particle beam may be applied to the patient at an ultra-high dose rate. The particle beam may be applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds. The particle beam may be applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds. The structures of the energy degrader may be controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient at an ultra-high dose rate of radiation.

0034The system may include an outer gantry on which the particle accelerator is mounted. The outer gantry may be controllable to move the particle accelerator at least part-way around the patient. The system may include an inner gantry that is controllable to move in concert with the outer gantry. The inner gantry may include a nozzle that is extendible towards, and retractable away from, the patient. The energy degrader may be located in the nozzle. The energy degrader is located in a treatment room in which the particle beam is applied to the patient. The nozzle may be retractable fully into the inner gantry.

0035The particle beam may have a spot size of less than 1.2 centimeters (cm) sigma for a particle beam having an energy of 70MeV or greater. The particle beam may have a spot size of less than 1.2 centimeters (cm) sigma. The particle beam may have a spot size of less than 0.5 centimeters (cm) sigma.

0036There may be no structures used to affect the particle beam between the energy degrader and the patient. The system may include a configurable collimator between the energy degrader and the patient. The configurable collimator may be controllable to trim the particle beam at a resolution as small as a single spot. The actuators may include linear motors. The actuators may include rotary motors that each drive a corresponding linear actuator to control movement of a corresponding structure.

0037One or more of the multiple structures in the energy degrader may include a composite material comprised of boron carbide and graphite. Each of the multiple structures in the energy degrader may be pure boron carbide.

0038Two or more of the features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein.

0039Control of the various systems described herein, or portions thereof, may be implemented via a computer program product that includes instructions that are stored on one or more non-transitory machine-readable storage media and that are executable on one or more processing devices (e.g., microprocessor(s), application-specific integrated circuit(s), programmed logic such as field programmable gate array(s), or the like). The systems described herein, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing devices and computer memory to store executable instructions to implement control of the stated functions.

0040The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

0041<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a perspective view of an example irradiation target treated by scanning a particle beam across entire layers sequentially.</li><li><figref idref="f0002">Fig. 2</figref> is a perspective view of an example irradiation target treated by scanning a particle beam column-by-column across the target.</li><li><figref idref="f0003">Fig. 3</figref> is a cut-away view of part of an example particle accelerator that is usable in the particle therapy system described herein.</li><li><figref idref="f0004">Fig. 4</figref> is a side view of components of an example scanning system that is usable in the particle therapy system described herein.</li><li><figref idref="f0005">Fig. 5</figref> is a perspective view of components of the example scanning system that is usable in the particle therapy system described herein.</li><li><figref idref="f0006">Fig. 6</figref> is a front view of an example magnet for use in a scanning system of the type shown in <figref idref="f0004">Figs. 4</figref> and <figref idref="f0005">5</figref>.</li><li><figref idref="f0006">Fig. 7</figref> is a perspective view of an example magnet for use in a scanning system of the type shown in <figref idref="f0004">Figs. 4</figref> and <figref idref="f0005">5</figref>.</li><li><figref idref="f0007">Fig. 8</figref> is a perspective view of an example energy degrader (e.g., range modulator) for use in a scanning system of the type shown in <figref idref="f0004">Figs. 4</figref> and <figref idref="f0005">5</figref>.</li><li><figref idref="f0008">Fig. 9</figref> is a perspective view of a process for moving a plate of the energy degrader into and out of the path of a particle beam.</li><li><figref idref="f0009">Fig. 10</figref> is a block diagram of example linear motors and example plates of an energy degrader controlled thereby.</li><li><figref idref="f0010">Fig. 11</figref> is a flowchart showing an example process for treating an irradiation target by scanning a particle beam column-by-column across the target.</li><li><figref idref="f0011">Figs. 12</figref>, <figref idref="f0012">13</figref>, <figref idref="f0013">14</figref>, and <figref idref="f0014">15</figref> are perspective block diagrams illustrating treatment of a column of an irradiation target by moving energy-absorbing plates sequentially into a path of a stationary particle beam.</li><li><figref idref="f0015">Figs. 16</figref>, <figref idref="f0016">17</figref>, <figref idref="f0017">18</figref>, and <figref idref="f0018">19</figref> are perspective block diagrams illustrating treatment of a column of an irradiation target by moving energy-absorbing plates sequentially out of a path of a stationary particle beam.</li><li><figref idref="f0019">Fig. 20</figref> is a front view of an example collimator containing a two-dimensional array of holes.</li><li><figref idref="f0020">Fig. 21</figref> is a front view of an example collimator containing a two-dimensional array of holes and control components for the collimator.</li><li><figref idref="f0021">Fig. 22</figref> is a perspective view of an example collimator containing a single linear array of holes.</li><li><figref idref="f0021">Fig. 23</figref> is a perspective view of the example collimator of <figref idref="f0021">Fig. 22</figref>.</li><li><figref idref="f0022">Fig. 24</figref> is a perspective view of an example collimator containing two linear arrays of holes that are not independently controllable.</li><li><figref idref="f0023">Fig. 25</figref> is a front view of an example collimator containing carriers that are independently controllable.</li><li><figref idref="f0024">Figs. 26</figref> and <figref idref="f0025">27</figref> are front and perspective views, respectively, of an example particle therapy system.</li><li><figref idref="f0026">Fig. 28</figref> is a perspective view of an example particle therapy system.</li><li><figref idref="f0027">Fig. 29</figref> is a graph showing changes in particle beam spot size for different particle beam energies for different materials used in the energy degrader to change the energy of the particle beam.</li><li><figref idref="f0028">Fig. 30</figref> is a front view of an example collimator containing a linear array of slots.</li><li><figref idref="f0029">Fig. 31</figref> is a front view of an example collimator containing a two-dimensional array of slots.</li><li><figref idref="f0030">Fig. 32</figref> is a front view of an example slot illustrating collimation performed by a slot on a particle beam.</li><li><figref idref="f0031">Fig. 33</figref> is a front view of an example collimator containing a linear array of slots showing movement of the particle beam along parts of the slots.</li><li><figref idref="f0032">Fig. 34</figref> is a diagram showing an example spread-out Bragg peak (SOBP) and a column that is part of example irradiation target.</li><li><figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042">Figs. 35 to 44</figref> are perspective block diagrams illustrating example processes for treating columns of an irradiation target by micro-volume.</li><li><figref idref="f0043">Figs. 45A and 45B</figref> are plots showing results of Monte Carlo simulations that calculate radiation dose delivered to a treatment volume and the time it takes for each voxel in that dose calculation to reach a final dose.</li><li><figref idref="f0044">Fig. 46</figref> is a perspective view of an example configurable collimator leaf that is usable with the example configurable collimators described herein.</li><li><figref idref="f0045">Fig. 47</figref> is a top view of configurable collimator leaves positioned relative to a treatment area of an irradiation target.</li><li><figref idref="f0046">Fig. 48</figref> is a perspective view of an example configurable collimator.</li><li><figref idref="f0046">Fig. 49</figref> is a front view of the example configurable collimator.</li><li><figref idref="f0047">Fig. 50</figref> is a perspective, view of the example configurable collimator having components portrayed in see-through to show the interiors thereof.</li><li><figref idref="f0048">Fig. 51</figref> is a perspective view of the example configurable collimator positioned relative to a patient during particle therapy treatment.</li></ul>

0042Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

0043Described herein are example implementations of particle therapy systems that include a collimator. The particle therapy systems are for treating an irradiation target ("target") in a patient, such as a tumor, using a particle beam such as a proton or ion beam. Some systems treat the target cross-sectional layer by layer. For example, the energy of the particle beam may be controlled to deliver a radiation dose ("dose") to a layer and then the particle beam may be moved across all or part of that layer. Thereafter, the energy of the particle beam may be changed to deliver dose to another layer. The particle beam may be moved across all or part of that other layer and so on until the entire target is treated. For example, <figref idref="f0001">Fig. 1</figref> shows treating an entire layer 10 of a target 11 using a particle beam 12 having an energy sufficient to deliver dose to layer 10 by moving the particle beam across the layer along the directions of arrows 15. Then a different layer 16 of the target 11 is treated in the same manner using a particle beam having a different energy sufficient to deliver dose to layer 16, and so on. The treatment of the whole treatment volume on average is typically at relatively small dose rates, such as 0.1 Gray-per-second. The particle beam often penetrates healthy tissue before reaching the target. Any one location within this healthy tissue may be visited several times over the course of treatment. The dose at such a location is received over a time scale on the order of minutes.

0044By contrast, some particle therapy systems may treat three-dimensional columns of the target using ultra-high (FLASH) dose rates of radiation. These systems scale the ultra-high dose rate deliveries to targets using pencil beam scanning. In some examples, pencil beam scanning includes delivering a series of small beams of particle radiation that can each have a unique direction, energy, and charge. By combining doses from these individual beams, a three-dimensional target treatment volume may be treated with radiation. Furthermore, instead of organizing the treatment into layers at constant energies, the systems organize the treatment into columns defined by the direction of a stationary beam. The direction of the beam may be toward the surface of the target.

0045In some implementations, all or part of a column is treated before the particle beam is directed along another path through the irradiation target. In some implementations, a path through the target is all or part-way through the target. In an example, the particle beam may be directed along a path through a target and not deviate from that path. While directed along that path, the energy of the particle beam is changed. The particle beam does not move as its energy changes and, as a result, the particle beam treats all or a part of an interior portion of the target that extends along a length of the particle beam and along a width of the beam spot. The treatment is thus depth-wise along a longitudinal direction of the beam. For example, a portion of the target treated may extend from a spot of the beam at the surface of the target down through all or part of an interior of the target. The result is that the particle beam treats a three-dimensional columnar portion of the target using an ultra-high dose rate of radiation. In some examples, ultra-high dose rates of radiation include, for example, doses of radiation that exceed 1 Gray-per-second for a duration of less than 500 milliseconds (ms), that exceed 1 Gray-per-second for a duration of between 10ms and 5 seconds (s), or that exceed 1 Gray-per-second for a duration of less than 5s. Other examples are provided herein.

0046In some implementations, after a column of the target has been treated as described in the preceding paragraph, the particle beam is directed along a new, different path through the target. For example, as shown in <figref idref="f0002">Fig. 2</figref>, a column 20 of target 21 is treated by varying the energy of a particle beam 22 that proceeds along the direction of arrow 28. The particle beam is then directed along a new path 24 through target 21 where it proceeds along the direction of arrow 29. A column 25 is then treated along that new path by varying the energy of the particle beam while the particle beam is stationary. As noted, the column is located along the longitudinal extent of the beam. In some implementations, the particle beam is directed along each path through the target only once when treating columns of the target. As a result, healthy tissue above or below target 21 is exposed to the ultra-high dose rate of radiation once but not to multiple low doses of radiation as occurs when targets are treated layer-by-layer as in <figref idref="f0001">Fig. 1</figref>.

0047In other words, in some implementations the particle beam is directed along a new path and upstream tissue along that path is never visited again. In this way, each location within the target can be treated at a rate that is comparable to that of an individual pencil beam modulated with the layer switching time. The average dose rate over the entire treatment may be comparable to layer-by-layer radiation deliveries, but the localized dose rate for any one spot is at an ultra-high dose rate. In some cases, a reduction in damage to healthy tissue may occur when radiation is delivered at ultra-high dose rates. For example, when delivering radiation doses of 10 to 20 Gray in pulses of less than 500ms - reaching effective dose rates of 20 to 100 Gray-per-second - healthy tissue may be less damaged than when irradiated with the same dose over a longer time scale, while the delivered radiation may treat tumors with the same level of effectiveness.

0048In some implementations, the operational speed of hardware used to produce and to condition the particle beam may affect the ability to deliver radiation at ultra-high dose rates. For example, in order to achieve ultra-high dose rates, the energy of the particle beam may be changed at a rate that exceeds changes of energy used for layer-by-layer scanning. For example, ultra-high dose rates applied to columns of a target may be achieved by switching beam energy in a duration of 50ms. This may be achieved, for example, by controlling motion of the particle beam and motion of energy-absorbing plates containing boron carbide or other structures containing boron carbide into and out of the path of the particle beam. By way of example, a 5 centimeter (cm) deep column, which might require 5 layer switches, may require 250ms of down-time during which particle beam is not delivered, allowing 250ms of beam delivery during which 10 to 20 Gray of dose may be delivered. Faster motion of the energy-absorbing plates and/or additional coordination of beam motion may further decrease the layer switching time allowing even more time to deliver the required treatment dose while still meeting the requirement for a localized ultra-high dose rate.

0049Also described herein are example implementations of a collimator for use with the particle therapy system. Use of a collimation to isolate adjacent spots (e.g., <figref idref="f0001">Fig. 1</figref>) or adjacent columns (e.g., <figref idref="f0002">Fig. 2</figref>) from each other may enable the system to achieve FLASH dose rates or non-FLASH dose rates in localized regions, such as a spot or a column, without the radiation leaking into adjacent regions or with minimal acceptable amounts of the radiation leaking into adjacent regions.

0050In some implementations, the collimator may include a carrier having one or more openings, such as one or more holes or slots, through which a particle beam passes to the target in the patient. The carrier may be a plate, a polyhedron, or a curved three-dimensional (3D) structure that is made of a material that inhibits passage of the particle beam. For example, the carrier may be made of a metal such as nickel, brass, or tungsten having a thickness sufficient to prevent passage of radiation at a given energy. In some implementations, the sizes and shapes of one or more of the openings are fixed; for example, the sizes and shapes are not changeable or configurable. For example, the shape and content of the collimator may be static. The particle beam is movable within an opening or between openings. Each opening trims the particle beam by allowing part of the particle beam to pass through the opening to reach the target in the patient while preventing a different part of the particle beam from reaching the patient. The trimming may collimate the particle beam. For example, as a result of the trimming, the amount of dispersion along the beam path may be reduced.

0051A control system, such as a computing system, may be configured to control movement of the particle beam to a first hole (an example of an opening) of the collimator to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first hole, and to control movement of the particle beam from the first hole to a second hole. The control system may also be configured to change an energy of the particle beam while the particle beam remains stationary at the second hole and to control movement of the particle beam from the second hole to multiple additional holes. At each of the multiple additional holes, the particle beam is controlled to remain stationary for a period of time while the energy of the particle beam changes. As a result, at each hole, the particle beam is trimmed and, by virtue of the energy change, the particle beam treats a three-dimensional column within the target.

0052The speed of operation of a collimator used in a particle therapy system may affect the system's ability to deliver radiation at ultra-high dose rates. The example collimator described herein may have limited or no configurability and therefore may reduce or eliminate the amount of time required to configure the collimator during treatment. As a result, the collimator may be particularly useful when delivering radiation at ultra-high (FLASH) dose rates. The collimator may, however, be used when delivering radiation at dose rates that are not ultra-high. In some implementations, a configurable collimator may be used.

0053Described below are example implementations of a particle therapy system configured to deliver radiation at ultra-high dose rates through three-dimensional columns of a target. In an example implementation, the particle therapy system is a proton therapy system. As described herein, an example proton therapy system scans a proton beam in three dimensions across an irradiation target in order to destroy malignant tissue. <figref idref="f0003">Fig. 3</figref> shows a cross-section of components 310 of an example superconducting synchrocyclotron that may be used to provide a particle (e.g., a proton) beam in the proton therapy system. In this example, components 310 include a superconducting magnet 311. The superconducting magnet includes superconducting coils 312 and 313. The superconducting coils are formed of multiple integrated conductors, each of which includes superconducting strands - for example, four strands or six strands - wound around a center strand which may itself be superconducting or non-superconducting. Each of the superconducting coils 312, 313 is for conducting a current that generates a magnetic field (B). The magnetic yokes 314, 315 or smaller magnetic pole pieces shape the magnetic field in a cavity 316 in which particles are accelerated. In an example, a cryostat (not shown) uses liquid helium (He) to conductively cool each coil to superconducting temperatures, e.g., around 4° Kelvin (K).

0054In some implementations, the particle accelerator includes a particle source 317, such as a Penning Ion Gauge - PIG source, to provide an ionized plasma column to cavity 316. Hydrogen gas, or a combination of hydrogen gas and a noble gas, is ionized to produce the plasma column. A voltage source provides a varying radio frequency (RF) voltage to cavity 316 to accelerate particles from the plasma column within the cavity. As noted, in an example, the particle accelerator is a synchrocyclotron. Accordingly, the RF voltage is swept across a range of frequencies to account for relativistic effects on the particles, such as increasing particle mass, when accelerating particles within the acceleration cavity. The RF voltage drives a dee plate contained within the cavity and has a frequency that is swept downward during the accelerating cycle to account for the increasing relativistic mass of the protons and the decreasing magnetic field. A dummy dee plate acts as a ground reference for the dee plate. The magnetic field produced by running current through the superconducting coils, together with sweeping RF voltage, causes particles from the plasma column to accelerate orbitally within the cavity and to increase in energy as a number of turns increases.

0055The magnetic field in the cavity is shaped to cause particles to move orbitally within the cavity. The example synchrocyclotron employs a magnetic field that is uniform in rotation angle and falls off in strength with increasing radius. In some implementations, the maximum magnetic field produced by the superconducting (main) coils may be within the range of 4 Tesla (T) to 20T at a center of the cavity, which falls off with increasing radius. For example, the superconducting coils may be used in generating magnetic fields at, or that exceed, one or more of the following magnitudes: 4.0T, 4.1T, 4.2T, 4.3T, 4.4T, 4.5T, 4.6T, 4.7T, 4.8T, 4.9T, 5.0T, 5.1T, 5.2T, 5.3T, 5.4T, 5.5T, 5.6T, 5.7T, 5.8T, 5.9T, 6.0T, 6.1T, 6.2T, 6.3T, 6.4T, 6.5T, 6.6T, 6.7T, 6.8T, 6.9T, 7.0T, 7.1T, 7.2T, 7.3T, 7.4T, 7.5T, 7.6T, 7.7T, 7.8T, 7.9T, 8.0T, 8.1T, 8.2T, 8.3T, 8.4T, 8.5T, 8.6T, 8.7T, 8.8T, 8.9T, 9.0T, 9.1T, 9.2T, 9.3T, 9.4T, 9.5T, 9.6T, 9.7T, 9.8T, 9.9T, 10.0T, 10.1T, 10.2T, 10.3T, 10.4T, 10.5T, 10.6T, 10.7T, 10.8T, 10.9T, 11.0T, 11.1T, 11.2T, 11.3T, 11.4T, 11.5T, 11.6T, 11.7T, 11.8T, 11.9T, 12.0T, 12.1T, 12.2T, 12.3T, 12.4T, 12.5T, 12.6T, 12.7T, 12.8T, 12.9T, 13.0T, 13.1T, 13.2T, 13.3T, 13.4T, 13.5T, 13.6T, 13.7T, 13.8T, 13.9T, 14.0T, 14.1T, 14.2T, 14.3T, 14.4T, 14.5T, 14.6T, 14.7T, 14.8T, 14.9T, 15.0T, 15.1T, 15.2T, 15.3T, 15.4T, 15.5T, 15.6T, 15.7T, 15.8T, 15.9T, 16.0T, 16.1T, 16.2T, 16.3T, 16.4T, 16.5T, 16.6T, 16.7T, 16.8T, 16.9T, 17.0T, 17.1T, 17.2T, 17.3T, 17.4T, 17.5T, 17.6T, 17.7T, 17.8T, 17.9T, 18.0T, 18.1T, 18.2T, 18.3T, 18.4T, 18.5T, 18.6T, 18.7T, 18.8T, 18.9T, 19.0T, 19.1T, 19.2T, 19.3T, 19.4T, 19.5T, 19.6T, 19.7T, 19.8T, 19.9T, 20.0T, 20.1T, 20.2T, 20.3T, 20.4T, 20.5T, 20.6T, 20.7T, 20.8T, 20.9T, or more. Furthermore, the superconducting coils may be used in generating magnetic fields that are outside the range of 4T to 20T or that are within the range of 4T to 20T but that are not specifically listed herein.

0056In some implementations, such as the implementations shown in <figref idref="f0003">Fig. 3</figref>, the relatively large ferromagnetic magnetic yokes 314, 315 act as returns for stray magnetic fields produced by the superconducting coils. In some systems, a magnetic shield (not shown) surrounds the yokes. The return yokes and the shield together act to reduce stray magnetic fields, thereby reducing the possibility that stray magnetic fields will adversely affect the operation of the particle accelerator.

0057In some implementations, the return yokes and shield may be replaced by, or augmented by, an active return system. An example active return system includes one or more active return coils that conduct current in a direction opposite to current through the main superconducting coils. In some example implementations, there is an active return coil for each superconducting main coil, e.g., two active return coils - one for each main superconducting coil. Each active return coil may also be a superconducting coil that surrounds the outside of a corresponding main superconducting coil concentrically.

0058By using an active return system, the relatively large ferromagnetic magnetic yokes 314, 315 can be replaced with magnetic pole pieces that are smaller and lighter. Accordingly, the size and weight of the synchrocyclotron can be reduced further without sacrificing performance. An example of an active return system that may be used is described in <patcit id="pcit0009" dnum="US8791656B"><text>U.S. Patent No. 8,791,656</text></patcit> entitled "Active Return System", the contents of which are incorporated herein by reference.

0059At or near the output of an extraction channel of the particle accelerator, there may be one or more beam shaping elements including a scanning system. Components of the scanning system may be mounted on, or otherwise attached to, a nozzle for positioning relatively close to the patient during treatment.

0060Referring to <figref idref="f0004">Fig. 4</figref>, in an example implementation, at the output of extraction channel 420 of synchrocyclotron 421 (which may have the configuration of <figref idref="f0003">Fig. 3</figref>) are example scanning components 422 that may be used to move the particle beam three-dimensionally over and through an irradiation target. <figref idref="f0005">Fig. 5</figref> also shows examples of the components of <figref idref="f0004">Fig. 4</figref>. These include, but are not limited to, one or more scanning magnets 424, an ion chamber 425, an energy degrader 426, and a collimator 428. Other components that may be down-beam of the extraction channel are not shown in <figref idref="f0004">Figs. 4</figref> or <figref idref="f0005">5</figref> and may include, for example, one or more scattering devices for changing beam spot size. An example scattering device includes a plate or range modulator that disperses the particle beam as the particle beam passes through the scattering device.

0061In an example operation, scanning magnet 424 is controllable in two dimensions (e.g., Cartesian XY dimensions) to position the particle beam in those two dimensions and to move the particle beam across at least a part of an irradiation target. Ion chamber 425 detects the dosage of the beam and feeds-back that information to a control system to adjust beam movement. Energy degrader 426 is controllable to move structures into, and out of, the path of the particle beam to change the energy of the particle beam and therefore the depth to which dose of the particle beam will be deposited in the irradiation target. Examples of such structures include, but are not limited to, energy-absorbing plates; polyhedra such as wedges, tetrahedra, or toroidal polyhedra; and curved three-dimensional shapes, such as cylinders, spheres, or cones. In this way, the energy degrader can cause the particle beam to deposit doses of radiation in the interior of an irradiation target to treat columns of the target. In this regard, when protons move through tissue, the protons ionize atoms of the tissue and deposit a dose along their path. The Bragg peak is a pronounced peak on the Bragg curve which plots the energy loss of ionizing radiation during its travel through tissue. The Bragg peak represents the depth at which most protons deposit within tissue. For protons, the Bragg peak occurs right before the particles come to rest. Accordingly, the energy of the particle beam may be changed to change the location of its Bragg peak and, therefore, where a majority of the dose of protons will deposit in depth in the tissue.

0062<figref idref="f0006">Figs. 6 and 7</figref> show views of an example scanning magnet 424. In this example, scanning magnet 424 includes two coils 441, which control particle beam movement in the X dimension, and two coils 442, which control particle beam movement in the Y dimension. Control is achieved, in some implementations, by varying current through one or both sets of coils to thereby vary the magnetic field(s) produced thereby. By varying the magnetic field(s) appropriately, the particle beam can be moved in the X and/or Y dimension across the irradiation target. The energy degrader described previously can move the beam in the Z dimension through the target, thereby enabling scanning in three dimensions.

0063Referring back to <figref idref="f0004">Fig. 4</figref>, a current sensor 427 may be connected to, or be otherwise associated with, scanning magnet 424. For example, the current sensor may be in communication with, but not connected to, the scanning magnet. In some implementations, the current sensor samples current applied to magnet 424, which may include current to the coil(s) for controlling beam scanning in the X dimension and/or current to the coil(s) for controlling beam scanning in the Y dimension. The current sensor may sample current through the magnet at times that correspond to the occurrence of pulses in the particle beam or at a rate that exceeds the rate that the pulses occur in the particle beam. The samples, which identify the magnet current, are correlated to detection of the pulses by the ion chamber described below. For example, the times at which pulses are detected using the ion chamber may be correlated in time to samples from the current sensor, thereby identifying the current in the magnet coil(s) at the times of the pulses. Using the magnet current, it thus may be possible to determine the location within the irradiation target where each pulse, and thus dose of radiation - that is, dose of particles - was delivered. The location of the dose delivered within the target may also be determined based on the configuration of the energy degrader, for example, based on the number of plates in the beam path.

0064During operation, the magnitude value of the magnet current may be stored for each location at which a dose is delivered, along with the amount (e.g., intensity) of the dose. A control system, which may be either on the accelerator or remote from the accelerator and which may include memory and one or more processing devices, may correlate the magnet current to coordinates within the irradiation target, and those coordinates may be stored along with the amount of the dose. For example, the location may be identified by depth-wise layer number and Cartesian XY coordinates or by Cartesian XYZ coordinates, with the depth-wise layer corresponding to the Z coordinate. In some implementations, both the magnitude of the magnet current and the coordinate locations may be stored along with the dose at each location. This information may be stored in memory either on, or remote from, the accelerator. This information may be used to track treatment of the target and to maintain a record of that treatment.

0065Ion chamber 425 detects dosage, such as one or more individual doses, applied by the particle beam to positions within the irradiation target by detecting the numbers of ion pairs created within a gas caused by incident radiation. The numbers of ion pairs correspond to the dose provided by the particle beam. That information is fed-back to the control system and stored in memory along with the time that the dose is provided. This information may be correlated to, and stored in association with, the location at which the dose was provided and/or the magnitude of the magnet current at that time, as described above.

0066Collimator 428 may be located down-beam of the scanning magnets and down-beam of the energy degrader, as shown in <figref idref="f0004">Figs. 4</figref> and <figref idref="f0005">5</figref>. The collimator may trim the particle beam on a spot-by-spot basis during movement of the particle beam from path to path through the target. The collimator may also trim the particle beam while the particle beam is stationary on the target and when the energy of the stationary particle beam changes to impact different portions of the interior of the target. For example, the particle beam may spread along its diameter as it enters the interior of the target. The collimator may be configured - for example, constructed - to trim the particle beam to account for that spread. For example, the collimator may be configured to reduce beam dispersion to and through the target and thereby maintain a more constant spot size.

0067As described below, in some examples, the collimator may include one or more openings, through which the particle beam may be steered. For example, the collimator may include multiple holes, such as circular holes, arranged in a one-dimensional array or in a multi-dimensional array. The sizes and shapes of the holes are not changeable or configurable in some examples. The particle beam may be moved to the holes in a specified sequence to treat portions of the target in the patient. Each hole may trim and collimate the particle beam. The holes may be positioned sufficiently close to each other to limit the amount that individual spots of the particle beam overlap. This may be done in order to limit exposure of healthy tissue above and below the target to a single dose of ultra-high dose rate radiation. In some implementations, the holes may be formed through a carrier, such as a substrate that inhibits or blocks the radiation. The carrier itself may be movable within the beam field based, for example, on movement of the particle beam. For instance, a carrier having a linear array of holes may be configured to track motion of the particle beam across the beam field. However, because the holes themselves do not need to be configured, the amount of time required for movement of the carrier does not prevent delivery of radiation at ultra-high dose rates.

0068In some implementations, the collimator may include one or more slots through the carrier instead of, or in addition to, holes. For example, the collimator may include a single linear slot having a lateral dimension that is sufficient to trim the particle beam and a longitudinal dimension that extends across at least part of the radiation target and that can accommodate multiple particle beam spots. In some implementations, the collimator may include multiple linear slots arranged in an array. The sizes and shapes of the slots are not changeable or configurable in some examples. The particle beam may be moved to parts of each slot, which performs collimation in the lateral dimension (and in the longitudinal dimension at the slot endpoints). In some implementations, the slots may be formed through a carrier, such as a substrate that inhibits or blocks the radiation. The carrier itself may be movable within the beam field based, for example, on movement of the particle beam. For instance, a carrier having a single slot may be configured to track motion of the particle beam across the beam field. However, because the slot itself does not need to be configured, the amount of time required for movement of the carrier does not prevent delivery of radiation at ultra-high dose rates.

0069<figref idref="f0007">Fig. 8</figref> shows an example range modulator 460, which is an example implementation of energy degrader 426. In some implementations, range modulator 460 may be located down-beam of the scanning magnets between the collimator and the patient. In some implementations, such as that shown in <figref idref="f0007">Fig. 8</figref>, the range modulator includes a series of plates 461. The plates may be made of one or more of the following example materials: polycarbonate such as LEXAN^™, carbon, beryllium, boron carbide, a composite material comprised of boron carbide and graphite, or a material of low atomic number. Other materials, however, may be used in place of, or in addition to, these example materials. In other implementations of the energy degrader that include polyhedra such as wedges, tetrahedra, or toroidal polyhedra, or curved three-dimensional structures, such as cylinders, spheres, or cones, these structures may be made of one or more of the following example materials: polycarbonate such as LEXAN^™, carbon, beryllium, boron carbide, a composite material comprised of boron carbide and graphite, or a material of low atomic number.

0070In some implementations, structures of the range modulator containing boron carbide may include only boron carbide; that is, the structures may be pure boron carbide. In some implementations, structures containing boron carbide may include boron carbide in combination with another material, such as graphite, polycarbonate, carbon, or beryllium. In some implementations, every structure - for example, plate, polyhedron, or curved three-dimensional structure - in the energy degrader may contain all or part boron carbide. In some implementations, different structures - for example, plates, polyhedra, or curved three-dimensional structures - in the energy degrader may include different materials. For example, one or more plates in the energy degrader may be made of pure boron carbide and one or more other plates of the same energy degrader may be made of or include one or more of polycarbonate, carbon, and/or beryllium. Other materials may also be used. For example, one or more plates or portions thereof in the energy degrader may be made of a composite material comprised of boron carbide and graphite.

0071One or more of the plates is movable into, or out of, the beam path to thereby change the energy of the particle beam and, thus, the depth at which most of the dosage of the particle beam is deposited within the irradiation target. Plates are moved physically into and out of the path of the particle beam. For example, as shown in <figref idref="f0008">Fig. 9</figref>, a plate 470 moves along the direction of arrow 472 between positions in the path of the particle beam 473 and outside the path of the particle beam. The plates are computer-controlled. Generally, the number of plates that are moved into the path of the particle beam corresponds to the depth at which scanning of an irradiation target is to take place. Thus, dosage from the particle beam can be directed into the interior of a target by appropriate control of one or more plates.

0072In some implementation, individual plates of range modulator 460 are each coupled to, and driven by, a corresponding motor 464. In general, a motor includes a device that converts some form of energy into motion. A motor may be rotary or linear, and may be electric, hydraulic, or pneumatic. For example, each motor may be an electrical motor that drives a lead screw to extend a plate into the beam field or to retract a plate out of the beam field, including to cause motion of the plate to track or to trail motion of the particle beam within the beam field. For example, each motor may be a rotary motor that drives a corresponding linear actuator to control movement of a corresponding structure. In some implementations, individual plates of range modulator 460 are each coupled to, and driven by, a corresponding actuator. In some examples, actuators include mechanical or electro-mechanical devices that provide controlled movements and that can be operated electrically by motors, hydraulically, pneumatically, mechanically, or thermally. In some examples, an actuator includes any type of motor that is operated by a source of energy, such as electric current, hydraulic fluid pressure, or pneumatic pressure, and that converts that energy into motion.

0073In some implementations, an energy degrader containing boron carbide structures (or structures comprised of other material) may be located in the treatment room where the particle beam is applied to the patient. For example, the energy degrader may be located between the scanning magnet and the patient. In an example, the energy degrader may be located in a nozzle on a system's inner gantry, examples of which are described with respect to <figref idref="f0024">Figs. 26</figref>, <figref idref="f0025">27</figref>, and <figref idref="f0026">28</figref>.

0074The energy degrader may be located close to the patient so as to limit the amount that the particle beam is scattered or dispersed following passage through one or more plates or other structures. In some implementations, the energy degrader may be located no more than four meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located no more than three meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located no more than two meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located no more than one meter from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located no more than one-half a meter from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located within the nozzle no more than four meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located within the nozzle no more than three meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located within the nozzle no more than two meters from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located within the nozzle no more than one meter from the patient along a beamline of the particle beam. In some implementations, the energy degrader may be located within the nozzle no more than one-half a meter from the patient along a beamline of the particle beam.

0075In general, boron carbide may be cheaper and safer to use than some other materials that may be used to degrade the energy of the particle beam, such as beryllium. In general, boron carbide has a relatively low atomic weight and a high density and may compare favorably in its scattering properties to some other materials that may be used to degrade the energy of the particle beam, such as carbon (e.g., graphite) and polycarbonate. Reducing the beam scattering results in a reduced beam spot size; that is, the cross-sectional size of the beam. A reduced spot size provides for improved conformality in a pencil beam scanning system and higher localized dose rate. In other words, reducing the spot size reduces the area over which dose is deposited. As a result, the concentration of protons deposited within a single spot increases, thereby increasing the dose rate within the area of the single spot. Increasing the dose rate within the area of the single spot is desirable when performing scanning using ultra-high (or "FLASH") dose rates since it facilitates deposition of an ultra-high dose of protons within a prescribed period. Examples of periods during which ultra-high doses are applied are described herein.

0076<figref idref="f0027">Fig. 29</figref> is a graph showing the change in particle beam spot size for different particle beam energies for different materials used in the energy degrader to change the energy of the particle beam. In this example, LEXAN^™, carbon (e.g., graphite), boron carbide, and beryllium are shown. According to the graph of <figref idref="f0027">Fig. 29</figref>, for example, a boron carbide degrader structure produces a particle beam having a spot size of less than 1.2 centimeters (cm) sigma at an energy of 70MeV (Million electron Volts). In this example, the spot size is measured at the output of the degrader structure. The spot may scatter the farther the beam travels through the air, which will cause an increase in spot size. However, placing the degrader sufficiently close to the patient will limit scattering. In addition, in some but not all cases, a collimator may be placed between the energy degrader and the patient to collimate the particle beam and thereby limit effects caused by scattering.

0077In addition to the foregoing advantages, a boron carbide based energy degrader may be reduced in size relative to energy degraders that use polycarbonate, for example. That is, a boron carbide based energy degrader may achieve substantially the same effect as a polycarbonate based energy degrader, but the boron carbide based energy degrader may have a smaller form factor than the polycarbonate based energy degrader. This is because the density of boron carbide is greater than the density of polycarbonate. In some examples, an energy degrader comprised of pure boron carbide plates may be 30 centimeters (cm) to 40cm thick along the beamline. The plates may have the same or varying thicknesses. The thickness of the plates and of the energy degrader itself will depend upon various factors such as the overall amount of energy change required and the number of layers to be treated, which may determine the number and thickness of each of the plates.

0078The reduced size of an energy degrader comprised of boron carbide makes the energy degrader less obtrusive in the treatment room. For example, an energy degrader comprised of all or some boron carbide structures may be housed within the nozzle on the inner gantry. The nozzle, including the energy degrader may be retracted fully within the inner gantry, thereby taking the energy degrader out of the way of a technician administering the treatment. In some implementations, the inner gantry may be flush with a wall of the treatment room, in which case retracting the nozzle and the energy degrader fully within the inner gantry causes the nozzle and energy degrader to retract fully within the wall.

0079<figref idref="f0009">Fig. 10</figref> shows an example implementation of a range modulator such as a boron carbide based range modulator that uses linear motors to control operations of energy-absorbing plates 101, 102, and 103. The range modulator of <figref idref="f0009">Fig. 10</figref> may otherwise have the configuration of the range modulator of <figref idref="f0007">Fig. 8</figref>. Although only three plates are shown in the example of <figref idref="f0009">Fig. 10</figref>, any appropriate number of plates may be included, as illustrated by ellipses 106.

0080Taking plate 102 as an example, an example linear motor that controls operation of plate 102 includes a movable component and stationary component comprised of two parts - in this example, magnets 110a and 11 0b. The two magnets are arranged side-by-side, with their poles aligned. That is, as shown, the positive pole (+) of magnet 110a is aligned to the positive pole (+) of magnet 110b, and the negative pole (-) of magnet 110a is aligned to the negative pole (-) of magnet 110b. The movable component includes a coil-carrying plate 109 between magnets 110a and 110b. Coil-carrying plate 109 is connected physically to energy-absorbing plate 102 and controls movement of energy-absorbing plate 102 along the directions of arrow 111, e.g., into and out of the path of the particle beam.

0081As explained, coil-carrying plate 109 includes one or more conductive traces or other conductive structures that pass current in order to generate a magnetic field. The magnetic field is controlled by controlling the current through the coil-carrying plate in order to control movement of the coil-carrying plate, and thus of energy-absorbing plate 102. That is, current through the coils generates a magnetic field that interacts with the magnetic field produced by magnets 110a and 110b. This interaction causes movement of coil-carrying plate 109 and of energy-absorbing plate 102 along the direction of arrow 111, either into, or out of, the particle beam path. For example, larger magnetic fields generated by the coil-carrying plate 109 may cause the energy-absorbing plate to move into the particle beam path and smaller or opposite magnetic fields generated by the coil-carrying plate may cause the energy-absorbing plate to retract away from the particle beam path.

0082In some implementations, the conductive traces or other conductive structures on the coil-carrying plate may include three windings embedded in aluminum. In some implementations, the energy-absorbing plate may be physically attached to the coil-carrying plate and move with the coil-carrying plate. In some implementations, the number of windings and the materials used may be different than those described herein. In some implementations, the coil-carrying plate may be an integral part of the energy-absorbing plate. For example, the energy-absorbing plate itself may include the conductive structures or traces.

0083As shown in <figref idref="f0009">Fig. 10</figref>, in some implementations, the current through the coil-carrying plates may be controlled by signals received from a control system, such as computing system 114. The computing system may be susceptible to neutron radiation and, therefore, may be located in a remote room 116. In some implementations, remote room 116 may be shielded from neutron radiation produced by the particle accelerator. In some implementations, the remote room may be located far enough away from the treatment room 117 so as not to be affected by neutron radiation from the particle accelerator. In some implementations, the computing system may be located in the treatment room, but may be shielded from neutron radiation emitted by the particle accelerator. In some implementations, all computing functionality is shielded from neutron radiation and the electronics that are not shielded can still operate in the presence of neutron radiation. Encoders are examples of such electronics.

0084In this regard, encoders (not shown) may include or more of laser sensors, optic sensors, or diode sensors. The encoders detect movement of the coil-carrying plates, e.g., by detecting where markings or other indicia on the coil-carrying plates or on structures connected to, and that move with, the coil-carrying plates are located relative to the encoders. This information about where the coil-carrying plates are is fed back to the computing system and is used by the computing system to confirm the position of the coil-carrying plates during operation. The encoders may be located at any appropriate location. In some implementations, the encoders are located on a housing that includes the coil-carrying plates. As the plates move, markings or other indicia that move with the coil-carrying plates move past the encoders. The encoders then relay that information to computing system 114. Computing system 114 may use that information to control operation of the range modulator, including positioning its energy-absorbing plates.

0085Computing system 114, which may be comprised of one or more processing devices, may be programmed to control the proton therapy system, including components of the scanning system to implement ultra-high dose rate radiation treatment column-by-column in an irradiation target. For example, the computing system may be controllable to output one or more control signals to control one or more of the linear motors to extend or to retract one or more of the energy-absorbing plates during scanning. For example, the computing system may be controllable to output one or more control signals to control one or more electrical motors to extend or to retract one or more of the energy-absorbing plates during scanning. The computing system may include one or more processing devices, such as microprocessors, microcontrollers, field-programmable gate arrays (FPGAs), or applications-specific circuits (ASICs), for example.

0086Referring to <figref idref="f0010">Fig. 11</figref>, the control system may be configured - for example, programmed - to implement a treatment plan for a target, such as tumor. The treatment plan may specify parameters including the dose rate of particle beam to use such as an ultra-high dose rate, the locations at which the dose is to be delivered to the target, and the sequence at which columns of the target are to be treated. Initially, the control system may control a particle accelerator - in this example, synchrocyclotron 310 - to generate (1101) a particle beam having specified parameters, including beam current and intensity. In some implementations, the beam current of the particle beam is 100 nanoamperes (nA) of current or less. In some implementations, the beam current of the particle beam is 50 nA of current or less. Levels of beam current on the order of nanoamperes may reduce risks of injury to the patient, may reduce risks of damage to the accelerator or other electronics in the treatment room, or may reduce risks of both such injury and damage.

0087The intensity of the particle beam may also be controlled (1102), or modulated, to control or to change the dose applied to the target at different particle beam energies. Thus, intensity-modulated proton therapy (IMPT) may be delivered using the techniques described herein. In some implementations, the same irradiation target may be treated using beams having different or the same intensities from multiple different angles either at FLASH dose rates or at dose rates lower than FLASH dose rates. For example, an irradiation target may be treated at FLASH or non-FLASH dose rates by delivering radiation by columns at different angles. In such examples, because the radiation is delivered at different angles, healthy tissue that is not being treated may be subjected to radiation only once.

0088The beam intensity is based, at least in part, on the number of particles in the particle beam. For example, the beam intensity may be defined by the number of particles in the particle beam. The intensity of the particle beam may change from spot to spot of the particle beam. Additionally, the intensity of one spot of the particle beam may be independent of the intensity of one or more other spots of the particle beam, including immediately horizontally-adjacent spots or vertically-adjacent spots. Accordingly, in some examples, any spot in a three-dimensional volume may be treated to an arbitrary dose independent of the dose to one or more adjacent spots. The control system may control particle beam intensity using one or more techniques.

0089In an example technique, the intensity of the particle beam can be controlled by varying the time duration of the pulses of particles obtained from the plasma column. In more detail, the RF voltage sweeps from a starting (e.g., maximum) frequency (e.g., 135 megahertz (MHz)) to an ending (e.g., minimum) frequency (e.g., 90 MHz). The particle source is activated for a period of time during the RF sweep to produce a plasma column. For example, in some implementations, the particle source is activated at 132 MHz for a period of time. During that time, particles are extracted from the plasma column by the electric field produced by the RF voltage. The particles accelerate outwardly in expanding orbits as the RF voltage frequency drops, keeping pace with the decreasing magnetic field and increasing relativistic mass until the particles are swept out at a time (e.g., about 600 microseconds) later. Changing the duration for which the particle source is activated changes the width of the pulse of particles that are extracted from the plasma column during a frequency sweep. Increasing the pulse width causes an increase in the amount of particles extracted and thus an increase in the intensity of the particle beam. Conversely, decreasing the pulse width causes a decrease in the amount of particles extracted and thus a decrease in the intensity of the particle beam.

0090In another example technique, the intensity of the particle beam can be controlled by changing a voltage applied to cathodes in the particle source. In this regard, the plasma column is generated by applying a voltage to two cathodes of the particle source and by outputting a gas, such as hydrogen (H₂), in the vicinity of the cathodes. The voltage applied to the cathodes ionizes the hydrogen and the background magnetic field collimates the ionized hydrogen to thereby produce the plasma column. Increasing the cathode voltage causes an increase in the amount of ions in the plasma column and decreasing the cathode voltage causes a decrease in the amount of ions in the plasma column. When more ions are present in the plasma column, more ions can be extracted during the RF voltage sweep, thereby increasing the intensity of the particle beam. When fewer ions are present in the plasma column, fewer ions can be extracted during the RF voltage sweep, thereby decreasing the intensity of the particle beam.

0091In another example technique, the intensity of the particle beam can be controlled by varying the amount of hydrogen supplied to the particle source. For example, increasing the amount of hydrogen supplied to the particle source results in more opportunity for ionization in the plasma column in response to the cathode voltage. Conversely, decreasing the amount of hydrogen supplied to the particle source results in less opportunity for ionization in the plasma column in response to the cathode voltage. As noted above, when more particles are present in the plasma column, more particles are extracted during the RF voltage sweep, thereby increasing the intensity of the particle beam. When fewer particles are present in the plasma column, fewer particles are extracted during the RF voltage sweep, thereby decreasing the intensity of the particle beam.

0092In another example technique, the intensity of the particle beam can be controlled by varying the magnitude of the RF voltage used to extract particles from the plasma column. For example, increasing the magnitude of the RF voltage causes more particles to be extracted from the plasma column. Conversely, decreasing the magnitude of the RF voltage causes fewer particles to be extracted from the plasma column. When more particles are extracted, the particle beam has a greater intensity than when fewer particles are extracted.

0093In another example technique, the intensity of the particle beam can be controlled by varying the starting time during the frequency sweep at which the particle source is activated and, thus, during which particles are extracted. More specifically, there is a finite window during the frequency sweep during which particles can be extracted from the plasma column. In an example implementation, the frequency sweeps from about 135 MHz to about 90 MHz at a substantially constant rate. In this example, particles can be extracted at about the beginning of the downward slope between starting and ending frequencies, e.g., between 132 MHz and 131 MHz respectively, and the particle source can be activated for a period of time, e.g., for about 0.1 microseconds (µs) to 100 µs (e.g., 1 µs to 10 µs or 1 µs to 40 ps). Changing the frequency at which the particle source is activated affects the amount of particles that are extracted from the particle beam and therefore the intensity of the particle beam.

0094In another example technique, pulse blanking may be used to control the intensity of the particle beam. In this regard, the RF frequency sweep is repeated a number of times per second (e.g., 500 times/second). The particle source could be activated for each frequency sweep (e.g., every 2 ms). Pulse blanking reduces the number of particles extracted from the particle beam by not activating the particle source during every frequency sweep. To achieve maximum beam intensity, the particle source may be activated every frequency sweep. To reduce beam intensity, the particle source may be activated less frequently, e.g., every second, third, hundredth, etc. sweep.

0095In another example technique, the intensity of the particle beam can be controlled by applying a DC bias voltage to one or more dees used to apply the RF voltage to the particle accelerator cavity. In this regard, the particle accelerator includes an active dee plate that is a hollow metal structure having two semicircular surfaces that enclose a space in which the protons are accelerated during their rotation around the cavity enclosed by the magnet yokes. The active dee is driven by an RF signal that is applied at the end of an RF transmission line to impart an electric field into the space. The RF field is made to vary in time as the accelerated particle beam increases in distance from the geometric center. A dummy dee may include a rectangular metal wall with a slot that is spaced near to the exposed rim of the active dee. In some implementations, the dummy dee is connected to a reference voltage at the vacuum chamber and magnet yoke.

0096Applying RF voltage in the presence of a strong magnetic field can cause multi-pactoring, which can reduce the magnitude of the RF field and, in some cases, cause an electrical short. To reduce the amount of multi-pactoring, and thereby maintain the RF field, DC (direct current) bias voltage may be applied to the active dee and, in some implementations, also to the dummy dee. In some implementations, the differential DC bias voltage between the active dee and dummy dee may be controlled to reduce multi-pactoring and thereby increase beam intensity. For example, in some implementations, there may be a 50% differential between the DC bias voltage on the active dee and dummy dee. In an example implementation, there is a -1.9 KV DC bias voltage applied to the dummy dee and there is a -1.5 KV DC bias voltage be applied to the active dee.

0097In another example technique, the intensity of the particle beam can be controlled by controlling the rate at which the RF voltage is swept - for example, the slope of the decrease. By decreasing the slope, it is possible to increase the amount of time during which particles can be extracted from the plasma column. As a result, more particles can be extracted, thereby increasing the intensity of the particle beam. The converse is also true, e.g., by increasing the slope, the amount of time during which particles can be extracted from the plasma column can be decreased, which can result in a decrease in particle beam intensity.

0098Implementations of the foregoing techniques for controlling the particle beam intensity are described in <patcit id="pcit0010" dnum="US9723705B"><text>U.S. Patent No. 9,723,705</text></patcit> entitled "Controlling Intensity Of A Particle Beam", the contents of which are incorporated herein by reference.

0099The control system may also control (1103) the spot size of the particle beam. As indicated above, one or more scattering devices may be moved into the path of the particle beam to change its spot size. In some implementations, the native spot size of the synchrocyclotron is the smallest spot size that is produced by the system. Since beam intensity is also a function of spot size, this spot size also produces the greatest beam intensity. In some implementations, the spot size that is producible by the system is less than 2 millimeters (mm) sigma. In some implementations, the spot size that is producible by the system is at least 2mm sigma. In some implementations, the spot size that is producible by the system is between 2mm sigma and 20mm sigma. In some implementations, the spot size that is producible by the system is greater than 20mm sigma. In some implementation, operation 1103 may be omitted.

0100The control system controls (1104) the scanning magnet to move the particle beam in accordance with the treatment plan to a path 24 through target 21, as shown in <figref idref="f0002">Fig. 2</figref> for example. Controlling the scanning magnet may include controlling the current through the coils of the scanning magnet (<figref idref="f0006">Figs. 6 and 7</figref>) that control movement of the particle beam in the Cartesian X dimension, controlling the current through coils of the scanning magnet that control movement of the particle beam in the Cartesian Y dimension, or both. At that location, the system delivers an ultra-high dose rate of radiation to a column that extends along the beam path through the target. In this example, the column includes interior portions of the target that are located along a direction 29 of the particle beam (<figref idref="f0002">Fig. 2</figref>). Column 25 is three dimensional in that it extends radially from the center of the beam spot to a perimeter of the spot and the column extends downward through the target. In some implementations, the column extends through the entirety of the target as shown in <figref idref="f0002">Fig. 2</figref>. In some implementations, the column extends only part-way through the target. In some implementations the column is entirely within an interior of the target. In some implementations, the column starts at one surface of the target and extends to an interior of the target but does not reach the other surface of the target. In some implementations, parts of adjacent columns overlap.

0101The column is treated (1105) using an ultra-high dose rate of radiation. Examples of ultra-high dose rates of radiation are described herein and include, but are not limited to, 1 Gray-per-second or more for a duration of less than 5s. The control system controls the energy of the particle beam while the particle beam is stationary so that the particle beam treats the column in the target. Treating the column in the target includes changing the energy of the particle beam so that, for each change in energy a majority of a dose of protons in the particle beam (its Bragg peak) deposits at a different depth within the target. As described herein, the energy of the particle beam may be changed by moving structures, which may be made of boron carbide or other particle energy degrading material, into or out of the path of the particle beam, as described with respect to the examples of <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref> and 35 to 44. All or some of the operations of <figref idref="f0010">Fig. 11</figref> may be repeated to treat different columns on an irradiation target. For example operations 1102, 1103, 1104, and 1105 may be repeated for each column to be treated on an irradiation target.

0102In implementations described below that use a variable-energy synchrocyclotron (or other type of variable energy particle accelerator), the energy of the particle beam may be changed by changing the current through the main coils of the synchrocyclotron. In some implementations, the energy of the particle beam is changed by moving structures, such as the energy-absorbing plates of range modulator 460, into and out of the path of the particle beam. In this regard, since the treatment plan specifies the locations of the columns on the target, the energy-absorbing plates of the range modulator may be pre-positioned proximate to those locations so as to reduce the time it takes for those plates to move into and out of position. Referring to <figref idref="f0011">Fig. 12</figref>, for example, plates 500 - which may be made from pure boron carbide or a boron carbide-graphite composite, for example - may be positioned proximate to column 501 in target 503 before treatment of column 501 with radiation begins. The plates may be moved from that location into the particle beam, thereby reducing the distance that the plates need to travel. That is, plates 500 may be configured to retract fully into the range modulator. The plates may be extended partially or fully prior to treatment and, as a result, need not travel from their fully retracted position in order to reach the path of the particle beam.

0103One or more of the plates may be controlled to move into and out of the path of the particle beam to change the energy of the particle beam, as noted. In an example, each of the one or more plates is movable into or out of the path of the particle beam in a duration of 100ms or less. In an example, each of the one or more plates is movable into or out of the path of the particle beam in a duration of 50ms or less. In an example, each of the one or more plates is movable into or out of the path of the particle beam in a duration of 10ms or less. In an example, each of the one or more plates is movable into or out of the path of the particle beam in a duration of 20ms or less or in a duration of 10ms or less. Use of linear motors, as described previously, may promote rapid movement of the plates, although electrical motors may be used as well. In this example, rapid movement includes movement on the order of tens of milliseconds.

0104One or more of the plates may be moved into and out of the path of the particle beam based on sequences defined in the treatment plan. For example, referring to <figref idref="f0011">Figs. 12</figref>, <figref idref="f0012">13</figref>, <figref idref="f0013">14</figref>, and <figref idref="f0014">15</figref>, a particle beam 504 is positioned by the scanning system to treat column 501 of target 503 at an ultra-high dose rate. In this example, to treat progressively shallower portions of column 501, treatment initially is performed with no plate in the path of the particle beam. This is shown in <figref idref="f0011">Fig. 12</figref>. The deepest part 502 of column 501 therefore is treated. In <figref idref="f0012">Fig. 13</figref>, plate 500a proceeds into the path of particle beam 504 along the direction of arrow 505 to reduce the energy of the particle beam. In this plate configuration, the second deepest part 506 of column 501 is treated. In <figref idref="f0013">Fig. 14</figref>, plate 500b also proceeds into the path of particle beam 504 along the direction of arrow 505 to reduce further the energy of the particle beam. In this plate configuration, the third deepest part 508 of column 501 is treated. In <figref idref="f0014">Fig. 15</figref>, plate 500c also proceeds into the path of particle beam 504 along the direction of arrow 505 to reduce further the energy of the particle beam. In this plate configuration, the shallowest part 510 of column 501 is treated. By changing the energy of particle beam 504 while particle beam 504 is stationary, the entirety of column 501 may be delivered ultra-high dose rate radiation. Examples of ultra-high dose rates are provided herein.

0105The particle beam may be directed by the scanning magnet to a new path through the target to treat a different column of target 503. The different column may be immediately adjacent to column 501 or may not be immediately adjacent to column 501. In some implementations, spots of the beam may overlap in part or not. For example, referring to <figref idref="f0015">Figs. 16</figref>, <figref idref="f0016">17</figref>, <figref idref="f0017">18</figref>, and <figref idref="f0018">19</figref>, a particle beam 604 is positioned by the scanning system to treat column 601 of target 503 at an ultra-high dose rate. In this example, to treat progressively deeper portions of column 601, treatment initially is performed with all plates 500a, 500b, and 500c in the path of the particle beam. This is shown in <figref idref="f0015">Fig. 16</figref>. The shallowest part 602 of column 601 therefore is treated first. In <figref idref="f0016">Fig. 17</figref>, plate 500c moves out of the path of particle beam 604 along the direction of arrow 605 to increase the energy of the particle beam. In this plate configuration, the second shallowest part 602 of column 601 is treated. In <figref idref="f0017">Fig. 18</figref>, plate 500b also moves out of the path of particle beam 604 along the direction of arrow 605 to increase further the energy of the particle beam. In this plate configuration, the third shallowest part 608 of column 601 is treated. In <figref idref="f0018">Fig. 19</figref>, plate 500c also moves out of the path of particle beam 604 along the direction of arrow 605 to increase further the energy of the particle beam. In this plate configuration, the deepest part 610 of column 601 is treated. By changing the energy of particle beam 604 while particle beam 604 is stationary, the entirety of column 601 may be delivered ultra-high dose rate radiation.

0106In some implementations, the plates need not be sequenced in order to treat a column. For example, plate 500a could be moved into the path of the particle beam first, followed by plate 500c, followed by plate 500b.

0107During delivery of ultra-high dose rate radiation to column 501 or 601, the intensity of particle beam 504 or 604 may be changed as necessary in order to deliver the ultra-high dose rate radiation specified in the treatment plan. Notably, the particle beam is stationary during delivery of the ultra-high dose rate radiation to each column. For example, while the ultra-high dose rate radiation is being delivered to different depths within the column, the path of the particle beam does not change relative to the target and the particle beam does not move. After the ultra-high dose rate radiation is delivered to the column, the particle beam is directed on a new path through the target. An ultra-high dose rate of radiation is then applied at that new path in the same manner as described with respect to <figref idref="f0010">Fig. 11</figref>. This process is repeated until all of the target is treated using the ultra-high dose rate radiation or until a designated part of the target is treated using the ultra-high dose rate radiation. In some implementations, the columns may be parallel as shown in the figures, with some or no overlap. In some implementations, at least some of the columns may not be in parallel resulting in overlap. In some implementations, sets of columns may be applied to the same target or micro-volume from different angles, thereby treating the target multiple times with radiation while preventing healthy tissue from being impacted by radiation more than once.

0108In some implementations, the particle beam is never again directed along paths that have already been treated using the ultra-high dose rate radiation. For example, the particle beam steps from path to path through target 503. In this example, each column extending into the target along a path is treated using the ultra-high dose rate radiation only once. Columns are not revisited and treated again. By treating columns only once using ultra-high dose rate radiation, healthy tissue above, and in some cases below, the target is less susceptible to damage from the radiation. Notably, however, the example systems described herein are not limited to treating each column only once using the ultra-high dose rate radiation. For example, in some implementations, each column may be revisited any appropriate number of times and subjected to one or more additional doses of ultra-high dose rate radiation. Furthermore, the example systems described herein are not limited to treating each column using only ultra-high dose rate radiation. For example, columns of a target may be treated as described herein using dose rates of radiation that are less than what would be considered an ultra-high dose rate. For instance, columns of a target may be treated as described herein using dose rates of radiation such as 0.1 Gray-per-second for a duration of one or more minutes. In some implementations, column-by-column treatment such as that shown in <figref idref="f0002">Fig. 2</figref> may be combined with layer-by-layer treatment such as that shown in <figref idref="f0001">Fig. 1</figref>. For example, the target may be treated column-by-column followed by layer-by-layer or treated layer-by-layer followed by column-by-column. In some implementations, part of the target may be treated column-by-column and part of the target may be treated layer-by-layer in each case with ultra-high dose rate radiation or less.

0109In some implementations, energy-absorbing plates of the range modulator may be sequenced differently for different columns on the target in order to reduce treatment time. For example, for a column 501, the plates may be moved sequentially into the particle beam as explained with respect to <figref idref="f0011 f0012 f0013 f0014">Figs. 12 to 15</figref>. Then, the particle beam may be directed to treat an adjacent - or other - column 601 of the target. If the plates already cover that path of the particle beam, they may be moved sequentially out of the path of the particle beam as described with respect to <figref idref="f0015 f0016 f0017 f0018">Figs. 16 to 19</figref>. If the plates do not already cover that path of the particle beam, the plates may be moved together to cover that path of the particle beam and then moved sequentially out of the path of the particle beam. Accordingly, for a first column, the plates may be moved sequentially to treat progressively shallower portions - for example, layers - of the first column. For a second column that is adjacent to the first column, the plates the plates may be moved sequentially to treat successively deeper portions - for example, layers - of the second column. This process may be repeated throughout the target for adjacent paths of the particle beam. In some implementations, movements of the plates may be incremental in the beam field; for example, based on the spot size (e.g., on the order of millimeters) rather than from their fully retracted position. For example, the plates may be moved from particle beam path to adjacent particle beam path rather than being fully retracted and extended for each column.

0110In some implementations, the energy-absorbing plates are movable across all or part of the beam field. In some examples, the beam field is the maximum extent that the beam can be moved across a plane parallel to the treatment area on a patient. One or more of the plates may track the particle beam as it moves from particle beam to adjacent particle beam. For example, one or more of the plates may move along with movement of the particle beam such that the particle beam passes through one or more of the plates while the plates move.

0111In some implementations, a dose of radiation that is less than an ultra-high (or FLASH) dose rate of radiation may be applied to the target layer-by layer using an energy degrader having structures such as plates, polyhedra, or curved three-dimensional shapes that are made of boron carbide. For example, referring to <figref idref="f0001">Fig. 1</figref>, an entire layer 10 of a target 11 may be treated using a particle beam 12 having an energy sufficient to deliver dose to layer 10 by moving the particle beam across the layer along the directions of arrows 15. The energy degrader may then be reconfigured - for example, a plate made of boron carbide may be moved out of the beam path to increase an energy level of the particle beam. Then a different layer 16 of the target 11 may be treated in the same manner using a particle beam having a different energy sufficient to deliver dose to layer 16, and so on.

0112In some implementations, FLASH doses of radiation may be delivered along a single column, with the beam direction fixed at a single spot at an isocenter of the particle accelerator. In some implementations, FLASH doses of radiation may be delivered using slightly larger localized volumes - referred to as micro-volumes - rather than columns aimed at a single spot. A micro-volume may be a voxel, part of a voxel, or include multiple voxels as specified in the treatment plan. <figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042">Figs. 35 to 44</figref> show an example of delivery of radiation by column using FLASH dose rates to micro-volumes of an irradiation target. Examples of FLASH dose rates are described herein. In some implementations, delivery of radiation by column to the micro-volumes of <figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042">Figs. 35 to 44</figref> may be at non-FLASH dose rates or combined FLASH dose rates and non-FLASH dose rates.

0113<figref idref="f0033">Fig. 35</figref> shows an example of part 1400 of an irradiation target, such as a tumor in a patient. Part 1400 is broken into four micro-volumes 1401, 1402, 1403, and 1404. Although cubical micro-volumes are shown, the micro-volumes may have any appropriate shape, such as three-dimensional orthotopes, regular curved shapes, or amorphous shapes. In this example, each micro-volume is treated through delivery of radiation by column in the manner described herein, for example with respect to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref>. For example, column depths of a micro-volume may be treated with radiation by using energy degrader plates to change the beam energy or by controlling a variable-energy synchrocyclotron to change the beam energy. After an individual micro-volume has been treated, the next micro-volume is treated, and so forth until the entire irradiation target has been treated. Treatment of the micro-volumes may be in any appropriate order or sequence.

0114In the example of <figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042 f0043 f0044">Figs. 35 to 46</figref>, only eight columns 1405 are shown. However, any appropriate number of columns may be treated per micro-volume. In some examples 10 to 20 spots, and thus columns, may treat a micro-volume. In addition, although each spot corresponds to a column of radiation, only the front columns are shown in the figures for clarity. Furthermore, although the example described herein treats the micro-volumes from the most deep part of the column to the most shallow part of the column, that need not be the case. For example, energy degrader plates may be controlled to treat one micro-volume from the most deep part of columns to the most shallow part of the columns and then treat the neighboring micro-volume from the most shallow part of the columns to the most deep part of the columns and so forth, as described with respect to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs.12 to 19</figref>. In other examples, different column depths may be treated non-sequentially.

0115In <figref idref="f0033">Fig. 35</figref>, the deepest parts 1407 of columns 1405 are treated. Treated parts of the columns are shaded and untreated parts are not shaded, as is the convention herein. In <figref idref="f0034">Fig. 36</figref>, the next deepest parts 1408 of columns 1405 are treated. In <figref idref="f0035">Fig. 37</figref>, the next deepest parts 1409 of columns 1405 are treated. In <figref idref="f0036">Fig. 38</figref>, the next deepest parts 1410 of columns 1405 are treated. In <figref idref="f0037">Fig. 39</figref>, the shallowest parts 1411 of columns 1405 are treated, thereby completing treatment of micro-volume 1401. In this regard, although the columns are separated for clarity, the columns may actually overlap at least in part as is the case with respect to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref> to ensure that the entire micro-volume is treated with radiation.

0116After micro-volume 1401 is treated, the next micro-volume 1402 is treated in a similar manner. In <figref idref="f0038">Fig. 40</figref>, the deepest parts 1417 of columns 1415 are treated. In <figref idref="f0039">Fig. 41</figref>, the next deepest parts 1418 of columns 1415 are treated. In <figref idref="f0040">Fig. 42</figref>, the next deepest parts 1419 of columns 1415 are treated. In <figref idref="f0041">Fig. 43</figref>, the next deepest parts 1420 of columns 1415 are treated. In <figref idref="f0042">Fig. 44</figref>, the shallowest parts 1421 of columns 1415 are treated, thereby completing treatment of micro-volume 1402. As was the case above, although the columns are separated for clarity, the columns may actually overlap at least in part as is the case with respect to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref> to ensure that the entire micro-volume is treated with radiation.

0117After micro-volume 1402 is treated, the remaining micro-volumes may be treated in a similar manner. The micro-volumes may be treated in any order or sequence and using any appropriate number and placement of columns. In addition, as described herein, individual columns may be treated using different bean intensities. These intensities may vary from column-to-column, from micro-volume-to-micro-volume or both from column-to-column and from micro-volume-to-micro-volume. Furthermore, each micro-volume may be treated from multiple different angles as part of intensity-modulated proton therapy treatment (IMPT).

0118In an example, plots of <figref idref="f0043">Figs. 45A and 45B</figref> show the results of Monte Carlo simulations that calculate radiation dose delivered to a treatment volume as well as the time it takes for each voxel in that dose calculation to reach the final dose. In an example, applying performance modifications to some parameters of a synchrocyclotron - for example, 10ms layer switching time instead of 50ms layer switching time, increasing the beam current, and enhancing pulse-pulse stability - spots delivered on a cube that is 3cm on each side can be delivered with every part of the treatment volume receiving its dose in less than 500ms. These small cubes were not strictly delivered in columns where each energy layer has a single spot, but rather in micro-volumes where each layer has a few (e.g., 10 to 20) spots. In addition, collimation may be used to isolate one micro-volume from another, allowing these volumes to be delivered in a reasonable amount of total treatment time. For example, the collimators described herein or any other appropriate collimating device, including standard multi-leaf collimators (MLC), may be used.

0119In some implementations, each micro-volume may be treated in the manner described with respect to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref>. For example, the entirety of a column in a micro-volume may be treated before moving on to a next column in the same micro-volume. Once all columns are treated in a micro-volume are treated, then treatment proceeds to the next micro-volume. There, treatment is repeated until all columns of the micro-volume are treated. Treatment then proceeds to the next micro-volume and so on until the entire irradiation target is treated. These implementations differ from the implementations of <figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042">Figs. 35 to 44</figref> in which an entire depth - or micro-layer - of each column in a micro-volume is treated at once for every column in that micro-volume. Thereafter, treatment proceeds to the next depth and so forth until all columns in the micro-volume have been treated.

0120Delivering radiation at ultra-high dose (FLASH) rates to all or part of a column as described herein may be implemented to deposit doses of radiation in any random manner. For example, referring to <figref idref="f0032">Fig. 34</figref>, an example column 1299 in a radiation target may be comprised of multiple depths. Each depth may comprise a micro-layer of the target that has about the diameter of a spot of the particle beam. Using delivery or radiation by column as described herein, radiation may be delivered to each of depths 1301, 1302, and 1303 at ultra-high dose (FLASH) rates. Doses may be delivered in any manner established by the treatment plan. For example, a higher dose of radiation may be applied to depth 1303 than to depths 1301 or 1302. In another example, the highest dose may be applied to depth 1303, the next highest dose may be applied to depth 1302, and the lowest dose may be applied to depth 1302. In another example, the highest dose may be applied to depth 1301, the next highest dose may be applied to depth 1303, and the lowest dose may be applied to depth 1302. Thus, doses may be applied without regard to - for example, independent of - the shape of a Bragg peak produced by summing the multiple doses. In other words, in some cases, the doses may not be configured to obtain a spread-out Bragg peak along a column of radiation delivered to an irradiation target at ultra-high dose (FLASH) rates or at lower dose rates.

0121In some implementations, one or more ridge filters or range modulator wheels may be added into the path of the particle beam to spread out - for example, to elongate - the Bragg peak of the particle beam. An elongated or spread-out Bragg peak is created by using a uniform depth-dose curve. That is, the dose is calibrated based on the depth in the tissue to which the dose is to be delivered in order to achieve an elongated Bragg peak that is flat or substantially flat. Referring to <figref idref="f0032">Fig. 34</figref>, for example, to achieve a spread-out Bragg peak such as 1300 using delivery of radiation by column, a full (100%) dose may be applied to depth 1301 in column 1299 of an irradiation target for a period of time. Next, an 80% dose may be applied to depth 1302 for a period of time. Depth 1302 is up-beam (that is, more shallow) than depth 1301. Next, a 66% dose may be applied to depth 1303 for a period of time. Depth 1303 is up-beam (that is, more shallow) than depth 1302. This may be repeated until spread-out Bragg peak 1300 is achieved.

0122Motors may control movement of the one or more ridge filters or range modulator wheels into or out of the path of the particle beam. The motors may be responsive to command of the control system. Spreading out the Bragg peak of the particle beam may be used for both columnar treatment as shown in <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">Figs. 12 to 19</figref> or layer-by-layer treatment as shown in <figref idref="f0001">Fig. 1</figref>. In some implementations, the intensity of the particle beam may be increased using techniques such as those described herein when the Bragg peak is spread-out.

0123In some implementations, a range modulator wheel may be robotically controlled to move in two dimensions or in three dimensions within the beam field so as to track movement of the particle beam. For example, the range modulator wheel may be robotically controlled to move in the Cartesian X, Y, and/or Z dimensions. The range modulator wheel may have varying thicknesses and may spin to change the Bragg peak of the particle beam and thus the depth within the target at which a majority of the particles are deposited. In some implementations, the range modulator wheel may include steps that define its various thicknesses. In some implementations, the intensity of the particle beam may be controlled in order to control the dose delivered at each location on the range modulator wheel. This may be done in order to control depth-dose distributions.

0124As explained above, the scanning system includes a collimator. The collimator may be controlled by the control system to trim the particle beam prior to the particle beam reaching the target in the patient. <figref idref="f0019">Fig. 20</figref> shows an example implementation of a collimator 700 that may be used with a particle therapy system such as those described herein. Collimator 700 includes a carrier 702. In this example, the carrier is a plate; however, the carrier may have any appropriate structure, such as a polyhedron or a three-dimensional curved structure such as cylinder, cone, or sphere. As previously explained, the carrier may be made of a metal or other material such as nickel, brass, or tungsten having a thickness sufficient to prevent passage of radiation at a given energy. For example, the carrier may be constructed - for example, have a thickness and a composition - to prevent passage of a proton beam having an energy of 100 MeV, 150 MeV, 200 MeV, 250 MeV, or 300 MeV. In this example, the openings 704 in the carrier include a two-dimensional 705 array of holes. The holes are circular in this example; however, any appropriately shaped hole may be used. For example, the holes may be oval, square, polygonal, or any other appropriate shape. The holes may be sized based on the size of the particle beam at the location of the collimator and based on the amount of trimming and collimation to be produced. In this regard, in some implementations, the spot size that is producible by the system is between 2mm sigma and 20mm sigma. The holes may be formed to produce collimation in this range. As explained previously, in some implementations, the sizes and/or shapes of the holes are not changeable or configurable. This may reduce the amount of time needed reconfigure the system when delivering ultra-high dose rate radiation. In some implementations, the sizes and/or shapes of the holes are configured to allow a predefined amount of bream spreading post collimation.

0125In some implementations, the carrier may be movable within, or across the entirety of, the beam field. As previously explained, in some examples, the beam field is the maximum extent that the particle beam can be moved across a plane parallel to the treatment area on a patient. In example collimator 720 of <figref idref="f0020">Fig. 21</figref>, carrier 708 may be mounted to a track 709 and connected to a belt 710 via physical couplings 711. A rotary motor 712 may drive belt 710 to move the carrier along the track to position the carrier within the beam field. For example, rotary motor 712 may be responsive to commands (shown as dashed line 715) from the control system 114 to position the carrier prior to treatment and to leave the carrier in place during treatment. In alternative implementations, the motor may be a rotary motor that drives a corresponding linear actuator to control movement of carrier across at least part of the beam field. In some implementations, the carrier may be moved during treatment. For example, the carrier may be moved based on movement of the particle beam. For instance, if the treatment area exceeds the dimensions of the collimator, the collimator may be moved by motor 712 in between treatment of columns to position the collimator to treat additional parts of the target. In another example, the collimator may be moved in concert with - that is, track - movement of the particle beam as the particle beam traverses the beam field.

0126In some implementations, the carrier may be movable in one, two, or three dimensions within the beam field. For example, as described above, the carrier may be mounted on a track to move through the beam field in one dimension. In some implementations, the carrier may be robotically controlled to move in two or three dimensions within the beam field. In some implementations, the track (and its associated assembly, such as the motor and the belt) to which the carrier is connected may itself be connected to a carriage (not shown) that is controllable to move in a dimension that is orthogonal to the track. For example, the carriage may be controlled by a motor that is responsive to one or more commands from the control system. The control system may therefore instruct movement of the carrier along the track and movement of the track via the carriage, thereby implementing two dimensional movement of the carrier within the beam field.

0127In some implementations, motion of the carrier may be monitored or determined using one or more encoders. In some examples, encoders include electronic devices that are connected to the carrier or to an assembly or structure that moves along with the carrier. The encoders may include or more of laser sensors, optic sensors, or diode sensors. The encoders detect movement of the carrier, e.g., by detecting where markings or other indicia on the carrier, or on structures that are connected to and that move with the carrier, are located relative to the encoders. Information about a location of the carrier is fed back to the control system and is used by the control system to confirm the position of the carrier and, in some implementations, to change its position. The encoders may be, or include, simple electronic sensors that are not particularly sensitive to neutron radiation and that, therefore, may be located in the treatment room.

0128As explained previously, in some implementations the collimator is used in implementing a treatment plan to deliver ultra-high dose rate radiation to columns of a target in a patient. To this end, the control system may be configured to control movement of the particle beam to a first hole 716 of collimator 720 to enable at least part of the particle beam to reach the patient through the first hole, to change an energy of the particle beam while the particle beam remains stationary at the first hole, and to control movement of the particle beam from first hole 716 to a second hole 717. In some implementations, the center of the particle beam spot - for example, the cross-sectional area of the particle beam - is positioned at the center of each hole. The energy of the particle beam may be changed by moving energy-absorbing structures into or out of the path of the particle beam or by changing a current through a superconducting magnet used in a variable-energy particle accelerator, as described herein. The motion (or "steering") of the particle beam may be controlled by varying or not varying the current through the scanning magnet described with respect to <figref idref="f0004 f0005 f0006">Figs. 4 to 7</figref>. The control system may also be configured to change an energy of the particle beam while the particle beam remains stationary at second hole 717 and to control movement of the particle beam from second hole 717 to multiple additional holes in a sequence that may be defined by the treatment plan. At each of the multiple additional holes, such as 721, 722, and 723 and so forth the particle beam is controlled to remain stationary for a period of time while the energy of the particle beam changes. As a result, at each hole, the particle beam is trimmed and, by virtue of the energy change, the particle beam treats a three-dimensional column within the target as described with respect to <figref idref="f0002">Figs. 2</figref>, <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018">12 to 19</figref>, and <figref idref="f0033 f0034 f0035 f0036 f0037 f0038 f0039 f0040 f0041 f0042">35 to 44</figref>. As previously explained, the openings such as the holes of <figref idref="f0020">fig. 21</figref> may be positioned relative to one another to achieve a desired amount of overlap, or no overlap, between adjacent columns in the target.

0129In some implementations, the collimator may be mounted within a nozzle on a system's inner gantry, examples of which are described with respect to <figref idref="f0024">Figs. 26</figref>, <figref idref="f0025">27</figref>, and <figref idref="f0026">28</figref>. In this regard, the collimator may be located down-beam of the energy degrader relative to the particle accelerator. In other words, the collimator may be located more near to the patient than the energy degrader. This is because the energy degrader may cause some dispersion of the particle beam and that dispersion may be reduced or corrected by the collimator. The nozzle may be configured to move the collimator towards or away from the patient. In addition, the nozzle, including the collimator, may be retracted fully within the inner gantry, thereby taking the collimator out of the way of a technician administering the treatment. In some implementations, the inner gantry may be flush with a wall of the treatment room, in which case retracting the nozzle and the collimator fully within the inner gantry causes the nozzle and collimator to retract fully within the wall.

0130<figref idref="f0021">Fig. 22</figref> shows an example implementation of a collimator 725 that includes a single linear array of holes. Except for the arrangement of the holes in the single linear array, the composition of collimator 725 and the structure of the holes may be the same as those of collimator 720. In this example, the carrier 726 that includes the holes is mounted to track 727 and connected to belt 728. Rotary motor 730 drives belt 728 either clockwise or counterclockwise, which causes carrier 726 to move in either direction of arrow 731 within frame 732. Motor 730 may be responsive to commands from the control system to cause carrier 731 to move when the particle beam is to move to an area adjacent to carrier 726. In an example, the control system may be configured to control movement of the particle beam to a first hole 735 of collimator 725 to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first hole, and to control movement of the particle beam from first hole 735 to a second hole 736. The control system may also be configured to change an energy of the particle beam while the particle beam remains stationary at second hole 736 and to control movement of the particle beam from second hole 736 downwards to multiple additional holes in the linear array defined by carrier 726. At each of the multiple additional holes, such as 737, 738, and 739 the particle beam is controlled to remain stationary for a period of time while the energy of the particle beam changes, thereby treating columns within the target at all hole locations.

0131When the particle beam is to move to another area, such as area 740 that is adjacent to the carrier, carrier 726 may first be moved to cover that area so that columns within the target underneath that area can be treated using ultra-high dose rate radiation as described previously. For example, as shown in <figref idref="f0021">Fig. 23</figref>, carrier 726 can be moved to area 740 and the particle beam can then be steered upwards through the holes in the carrier to treat columns within the target as described previously. This process may be repeated until the desired amount of the target is treated using ultra-high dose rate radiation. Although not shown in <figref idref="f0021">Figs. 22 and 23</figref>, collimator 725 can be mounted to a carriage that is controllable to move in a dimension that is orthogonal to track 727. For example, the carriage may be controlled by a motor that is responsive to one or more commands from the control system. The control system may therefore instruct movement of carrier 726 along track 727 and movement of track 727 via the carriage, thereby implementing two dimensional movement of the carrier within the beam field. As noted, the collimator may also be connected to the nozzle, thereby allowing an additional dimension of movement towards or away from the patient.

0132<figref idref="f0022">Fig. 24</figref> shows a variation on collimator 725 of <figref idref="f0021">Figs. 22 and 23</figref>. In this example collimator 742, there are two carriers 744 and 745 each including a linear array of holes. Except for the arrangement of the holes into two linear arrays, the composition of collimator 742 and the structure of the holes may be the same as for collimator 725. In this example, the two carriers may be physically connected to move along track 747 in concert. As explained above, the two carriers 744 and 745 are mounted to track 747 and connected to belt 749. Rotary motor 750 drives belt 749 either clockwise or counterclockwise, which causes the two carriers to move in either direction of arrow 752 within frame 753. Motor 750 may be responsive to commands from the control system to cause the carriers to move in order to comply with a treatment plan. In example, the control system may be configured to control movement of the particle beam to a first hole 755 of carrier 744 to enable at least part of the particle beam to reach the patient through the first hole, to change an energy of the particle beam while the particle beam remains stationary at the first hole, and to control movement of the particle beam from first hole 755 to a second hole 756. The control system may also be configured to change an energy of the particle beam while the particle beam remains stationary at second hole 756 and to control movement of the particle beam from second hole 756 downwards to multiple additional holes in the linear array of holes defined by carrier 744. At each of the multiple additional holes the particle beam is controlled to remain stationary for a period of time while the energy of the particle beam changes, thereby treating columns within the target. Thereafter, the particle beam can be steered to carrier 745 and upwards through the holes in carrier 745 to treat columns within the target underneath carrier 745. This process may be repeated until the desired amount of the target is treated using ultra-high dose rate radiation. Although not shown in <figref idref="f0022">Fig. 24</figref>, collimator 742 can be mounted to a carriage that is controllable to move in a dimension that is orthogonal to track 747. For example, the carriage may be controlled by a motor that is responsive to one or more commands from the control system. The control system may therefore instruct movement of the carriers along track 747 and movement of track 747 via the carriage, thereby implementing two dimensional movement of the carrier within the beam field. In some implementations different carriers 744 and 745 may be immediately adjacent or touching or there may be a separation 758 between the two as shown in <figref idref="f0022">Fig. 24</figref>. As noted, the collimator may also be connected to the nozzle, thereby allowing an additional dimension of movement towards or away from the patient.

0133In some implementations, as shown in <figref idref="f0023">Fig. 25</figref>, carriers 761 and 762 (which may have the same configuration as carriers 744 and 745, respectively) may be mounted to separate tracks 764 and 765, connected to separate belts 767 and 768, and controlled by separate rotary motors 770 and 771 that are each responsive to commands from the control system. The carriers 761 and 762 may thus be controlled to move independently of each other and relative to each other in order to implement ultra-high dose rate delivery of radiation in accordance with the treatment plan. Each part of collimator 760 and its associated assembly may have the same or similar structure and function as a corresponding part collimator 725.

0134Although not shown in <figref idref="f0023">Fig. 25</figref>, collimator 760 can be mounted to a carriage that is controllable to move in a dimension that is orthogonal to tracks 764 and 765. For example, the carriage may be controlled by a motor that is responsive to one or more commands from the control system. The control system may therefore instruct movement of the carriers along tracks 764 and 765 and movement of tracks 764 and 765 via the carriage, thereby implementing two dimensional movement of the carrier within the beam field. In some implementations, each of carriers 761 and 762 may be mounted to separate carriages, thereby enabling independent second dimensional movement of each of carriers 761 and 762. As noted, the collimator may also be connected to the nozzle, thereby allowing an additional dimension of movement towards or away from the patient.

0135In this regard, <figref idref="f0022">Figs. 24</figref> and <figref idref="f0023">25</figref> each shows two carriers, each containing a single linear array of holes. In some implementations, collimator 742 or 760 may include two or more carriers, each containing a linear array of holes or a two-dimensional array of holes. Each carrier may be physically connected as in <figref idref="f0022">Fig. 24</figref> to move together, or each carrier may be independently coupled as in <figref idref="f0023">Fig. 25</figref> and independently movable in response to commands from the control system. In addition, each carrier may be connected to enable second dimension movement using one or more carriages, as described previously. In some implementations, two motors may be configured to move carriers, such as carriers 761 and 762, along a single same track independently of each other.

0136In some implementations, the openings through which particle beam passes may be slots instead of holes. An example slot is rectangular in shape and may extend over and across locations over a target where two or more spots of the particle beam are to be delivered. Any of the carriers shown in the implementations of <figref idref="f0019 f0020 f0021 f0022 f0023">Figs. 20 to 25</figref> may include slots as openings instead of holes. For example, each linear array of holes in <figref idref="f0019 f0020 f0021 f0022 f0023">Figs. 20 to 25</figref> may be replaced by a single slot or two or more adjacent slots. In this regard, <figref idref="f0028">Fig. 30</figref> shows an example collimator 780 having an array of slots 781. In this example, the slots extend the entire length of the carrier. However, the slots may extend part-way down the carrier. For example, referring to <figref idref="f0029">Fig. 31</figref>, a collimator 783 may include a two-dimensional array of slots 784, with each individual slot extending about half-way down carrier 783.

0137The slots may be configured to trim and therefore collimate the particle beam in one dimension. For example, as shown in <figref idref="f0030">Fig. 32</figref>, example slot 788 collimates particle beam spot 790 by allowing part 791 of particle beam to pass through to the patient and to block parts 792 and 793 of the particle beam. At ends of the slots, such as end 794, the particle beam may be collimated in two dimensions. As was the case with collimators that use holes, collimators that use slots may also be used in implementing ultra-high dose rate radiation therapy.

0138Referring to example collimator 800 <figref idref="f0031">Fig. 33</figref> for example, the control system may control movement of the particle beam to a first part 801 of slot 798 to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first part 801 of slot 798, and to control movement of the particle beam from the first part 801 of slot 798 to a second part 802 of slot 798. The control system is also configured to change an energy of the particle beam while the particle beam remains stationary at the second part 802 of slot 798, and to control movement of the particle beam from the second part 802 of slot 798 to multiple additional parts 803 and 804 of slot 798. For example, the particle beam may be moved along slot 798 and deliver radiation at discrete locations along the slot. The particle beam is controlled to remain stationary for a period of time at each of the multiple additional parts of the slot while the energy of the particle beam changes at each part thereby treating columns of the target. The particle beam may then be moved to part 805 of slot 799 and proceed upwards along slot 799 depositing radiation in columns. Thus, a collimator that uses slots for openings may still be used to deliver ultra-high dose rate radiation by column to a target in a patient. Overlap between adjacent spots of the particle beam may be controlled in the treatment plan by controlling the current through the scanning magnet to position the spots at appropriate locations. In some implementations, use of slots may increase treatment speed and reduce the generation of stray neutrons that occurs when proton beams are trimmed.

0139Although the various implementations of the collimator described, for example, with respect to <figref idref="f0019 f0020 f0021 f0022 f0023">Figs. 20 to 25</figref> and <figref idref="f0028 f0029 f0030 f0031">30 to 33</figref> are described for use with ultra-high dose rate radiation treatment column-by-column, any implementation of such a collimator may be used in the delivery of doses of radiation that are not at ultra-high dose rates and/or that are not delivered in columns. For example, any collimator described herein may be used in implementing the layer-by-layer scanning approach described with respect to <figref idref="f0001">Fig. 1</figref>. Furthermore, the collimator implementations described show openings having the same shapes that are regularly arranged on a carrier. In some implementations, openings on the same carrier may have different sizes and/or shapes that may be dictated, for example, by the treatment plan. In addition, the openings may be arranged in an irregular pattern that may be dictated, for example, by the treatment plan. In some implementations, a carrier may include holes only, slots only, or a combination of both slots and holes. In some implementations, a carrier may have a single opening, such as a hole or a slot. The carrier and the particle beam may move in concert.

0140In some implementations, the example particle therapy system may include a configurable collimator instead of, or in addition to, the example collimators described with respect to <figref idref="f0019 f0020 f0021 f0022 f0023">Figs. 20 to 25</figref> and <figref idref="f0028 f0029 f0030 f0031">30 to 33</figref>. An example of a configurable collimator that may be used is described in <patcit id="pcit0011" dnum="US20170128746A"><text>U.S. Patent Publication No. 2017/0128746</text></patcit> entitled "Adaptive Aperture", the contents of which are incorporated herein by reference.

0141<figref idref="f0044">Fig. 46</figref> shows an example of a leaf 859 that may be used in the configurable collimator, although the configurable collimator is not limited to use with this type of leaf. The height 850 of the leaf is along the beamline (e.g., the direction of the particle beam). The length 852 of the leaf is along its direction of actuation into and out of the treatment area, and is based on the field size, or portion thereof, that the system can treat. The field size corresponds to the treatment area that the beam can impact. The width 853 of the leaf is the direction along which multiple leaves stack when actuated. Generally, the more leaves that are used, the higher the resolution of the aperture that can be produced, including for curved boundaries.

0142In <figref idref="f0044">Fig. 46</figref>, leaf 859 includes a tongue and groove feature 855 along its side, which is configured to reduce inter-leaf leakage when multiple such leaves stack. In this example, the curved end 856 of leaf 859 is configured to maintain a surface tangent to the beam at all locations in the treatment area. However, the end of each leaf may be flat, not curved.

0143In some implementations, the configurable collimator leaves have a height that is sufficient to block at least the maximum beam energy (e.g., the maximum energy of the particle beam output by the accelerator). In some implementations, the configurable collimator leaves have a height that blocks less than the maximum beam energy. In some implementations, the configurable collimator leaves have lengths that are dictated not by the area of an entire treatment area, but rather by the area of a single beam spot (the cross-sectional area of the particle beam) or multiple beam spots.

0144<figref idref="f0045">Fig. 47</figref> shows an example implementation of part a configurable collimator 810. Configurable collimator 810 includes leaves 811 having a height and made of a material, such as nickel, brass, tungsten, or other metal, sufficient to inhibit or prevent passage of radiation at a given energy. For example in some systems, a particle accelerator is configured to generate a particle beam having a maximum energy of 100 MeV (million electron-volts) to 300 MeV. Accordingly, in such systems, the leaves may be constructed to prevent passage of a beam having an energy of 100 MeV, 150 MeV, 200 MeV, 250 MeV, 300 MeV, and so forth. For example in some systems, a particle accelerator is configured to generate a particle beam having a maximum energy that exceeds 70 MeV. Accordingly, in such systems, the leaves may be constructed to prevent passage of a beam having an energy of 70 MeV or more.

0145Leaves 811 are mounted on carriages to control their movement relative to a treatment area of an irradiation target, such as a cross-sectional layer of a tumor in a patient. The movement is controlled to cause leaves 811 to cover some parts of treatment area 814, thereby preventing radiation from impacting those parts during treatment, while leaving other parts of treatment area exposed to the radiation. In the example implementation of <figref idref="f0045">Fig. 47</figref>, there are fourteen leaves in total, seven on the left and seven on the right. In some implementations, there may be a different number of leaves, e.g., ten in total, five on the left and five on the right, twelve in total, six on the left and six on the right, and so forth.

0146In <figref idref="f0045">Fig. 47</figref>, locations 812 represent centers of beam spots and thus the locations of columns in the target to which radiation is to be delivered. Circle 818 represents parts of a treatment boundary beyond which no radiation is intended to be delivered. Beam spots that are close to this boundary (e.g., within one standard deviation of the particle beam's profile) border healthy tissue. These spots may be trimmed (that is, blocked) by appropriate configuration and placement of leaves on the configurable collimator. An example of a beam spot to be trimmed is beam spot 816, having its center at location 816. As shown, leaves 811 are configured to block the portion of beam spot 816 that extends beyond circle 818 and into healthy tissue (or at least tissue not designated for treatment).

0147In an example implementation, on each of two separate carriages, there are five leaves that are about 5mm in width and two leaves that are about 81 mm in width. In some implementations, on each of two separate carriages, there are seven leaves, two of which each have widths that are three times or more the widths of each of five other leaves. Other implementations may contain different numbers, sizes, and configurations of leaves, and different numbers and configurations of carriages. For example, some implementations may include any number between five and fifty leaves per carriage, e.g., 5, 6, 7, 8, 9, 10, 11, 2, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 leaves (or more) per carriage.

0148The carriages can move both horizontally and vertically, as described herein. The leaves are also movable horizontally relative to each carriage into, and out of, the treatment area. In this way, the leaves are configurable to approximate the shape of the treatment boundary in the region near the area being treated (e.g., circle 816 or a portion thereof in this example).

0149The leaves may be moved vertically and/or horizontally between different columns to be treated so that the leaves are in appropriate positions when the beam is delivered to a particular column. As noted, the leaves may be reconfigured while the beam is stationary and based on beam energy to provide different configurations for different beam energies. As explained, the beam may disperse somewhat in tissue. The configurable collimator may be reconfigured as beam energy changes to maintain a regularly (e.g., cylindrically) shaped column.

0150<figref idref="f0046">Figs. 48, 49</figref>, and <figref idref="f0047">50</figref> show an example implementation of a configurable collimator, including carriages 913, 914, 915 configured to hold, and to move, the leaves described above both vertically and horizontally relative to the treatment target. As shown, vertical movement includes movement in the Cartesian Z-dimension 917, and horizontal movement includes movement in the Cartesian X dimension 918 (with the Cartesian Y dimension being into, or out of, the page in <figref idref="f0046">Fig. 49). Figs. 49</figref> and <figref idref="f0047">50</figref> show parts of carriage housings as transparent in order to show components inside the housings; however, the housings are not actually transparent.

0151Carriage 913 is referred to herein as the primary carriage, and carriages 914 and 915 are referred to herein as secondary carriages. Secondary carriages 914, 915 are coupled to primary carriage 913, as shown in <figref idref="f0046 f0047">Figs. 48 to 50</figref>. In this example, secondary carriages 914, 915 each include a housing that is fixed to primary carriage 915 via a corresponding member 918, 919. In this example, primary carriage 913 is movable vertically (the Z dimension) relative to the irradiation target and relative to particle accelerator along tracks 920. The vertical movement of primary carriage 913 also causes the secondary carriages to move vertically. In some implementations, the secondary carriages move vertically in concert. In some implementations, vertical movement of each secondary carriage is independent of vertical movement of the other secondary carriage.

0152As shown in <figref idref="f0046 f0047">Figs. 48 to 50</figref>, each secondary carriage 914, 915 is connected to a corresponding rod or rail 922, 923, along which the secondary carriage moves. More specifically, in this example, motor 925 drives secondary carriage 914 to move along rod 922 towards or away from secondary carriage 915. Likewise, in this example, motor 926 drives secondary carriage 915 to move along rod 923 towards or away from secondary carriage 914. Control over movement of the primary and secondary carriages is implemented to position the leaves relative to the irradiation target, as described herein. In addition, the leaves themselves are also configured to move in and out of the carriages, as also described herein.

0153As shown in <figref idref="f0047">Fig. 50</figref>, a motor 930 drives the vertical movement of primary carriage 913. For example, as shown in <figref idref="f0047">Fig. 50</figref>, lead screw 931 is coupled to housing 932, which holds motors 925, 926 that drive corresponding secondary carriages 914, 915, and which is mounted on tracks 920. Lead screw 931 is coupled to, and driven vertically by, motor 930. That is, motor 930 drives lead screw 931 vertically (the Cartesian Z dimension). Because lead screw 931 is fixed to housing 932, this movement also causes housing 932, and thus secondary carriages 914, 915, to move along tracks 920, either towards or away from the irradiation target.

0154In this example implementation, as noted, seven leaves 935, 936 are mounted on each secondary carriage 914, 915. Each secondary carriage may be configured to move its leaves horizontally into, or out of, the treatment area. The individual leaves on each secondary carriage may be independently and linearly movable using linear motors in the X dimension relative to other leaves on the same secondary carriage. In some implementations, the leaves may also be configured to move in the Y dimension. Furthermore, the leaves on one secondary carriage 914 may be movable independently of the leaves on the other secondary carriage 915. These independent movements of leaves on the secondary carriages, together with the vertical movements enabled by the primary carriage, allow the leaves to be moved into various configurations. As a result, the leaves can conform, both horizontally and vertically, to treatment areas that are randomly shaped both in horizontal and vertical dimensions. The sizes and shapes of the leaves may be varied to create different conformations. For example, the sizes and shapes may be varied to treat a single beam spot and, thus, a single column. In some implementations individual leaves on each secondary carriage may be independently and linearly movable using electric motors that drive lead screws in the X dimension relative to other leaves on the same secondary carriage.

0155The leaves may be made of any appropriate material that prevents or inhibits transmission of radiation. The type of radiation used may dictate what material(s) are used in the leaves. For example, if the radiation is X-ray, the leaves may be made of lead. In the examples described herein, the radiation is a proton or ion beam. Accordingly, different types of metals or other materials may be used for the leaves. For example, the leaves may be made of nickel, tungsten, lead, brass, steel, iron, or any appropriate combinations thereof. The height of each leaf may determine how well that leaf inhibits transmission of radiation.

0156In some implementations, the leaves may have the same height, whereas in other implementations, some of the leaves may have heights that are different from heights of others of the leaves. For example, a set of leaves may each be 5mm in height. However, any appropriate heights may be used. For example, leaves 935, 936 may have any of the following (or other heights): 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11 mm, 3mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, and so forth. The leaves may have any combination of the foregoing heights. In addition, each of the leaves may have a different height than one or more others of the leaves.

0157In some implementations, the leaves have heights that are enough not only to fully stop a particle beam at the maximum expected proton energy (e.g., 3.3cm of Tungsten at 230 MeV or, e.g., 5.2cm of nickel), but also to have enough extra material to prevent proton transmission between the leaves. This material may have a tongue and groove structure as shown in <figref idref="f0044">Fig. 46</figref>, or a similar configuration. The leaf ends may be configured to include curved or tapered surfaces to enhance delivered penumbra for proton beams of various divergence.

0158In some implementations, there may be more than one primary carriage and corresponding motors and rails. For example, a first primary carriage may control vertical movement of a first secondary carriage, and a second primary carriage may control vertical movement of a second secondary carriage. Therefore, in such implementations, the two secondary carriages can be moved independently in the vertical dimension, if desired. In any case, the primary carriage may be computer controlled. For example, executable instructions are stored in computer memory (e.g., one or more non-transitory machine-readable storage media), and executed by one or more processing devices to control the movement. Control may be performed with, or without, user input during treatment.

0159As explained, each secondary carriage 914, 915 includes a corresponding motor to control horizontal carriage movement, as described above. In some implementations, all leaves on a single carriage are independently movable using linear motors - with one linear motor controlling each leaf. Each leaf may be controlled by a linear motor of the type described in <figref idref="f0009">Fig. 10</figref> to create an edge to block at least some radiation from reaching the patient, e.g., to trim one or more spots produced by the particle beam. As noted, a linear motor used in the configurable collimator may have the same structure and function as a linear motor used with the range modulator. In this case, however, the collimator leaf is attached to the linear motor instead of an energy-absorbing plate. Each linear motor drives its corresponding leaf linearly to reach its position in a configured edge.

0160In the example implementations described above, each leaf is independently actuated using a separate, and independently-controllable, linear motor such that any appropriate shape can be traced with a leaf configuration. It may be, however, that such flexibility is not required to achieve acceptable edge conformality. The leaves could be mechanically constrained with the ability to achieve only a finite number of configurations. For example, the leaves could be restricted to arrangements that put them in a vertical line, forward diagonal shape, backward diagonal shape, concave shape, convex shape, or any other achievable shape. In this way, flexibility could be traded for mechanical simplicity.

0161In some cases, better beam performance (penumbra or edge sharpness) results when the particle beam is tangent to the surface of a leaf edge. However, since the beam effectively originates from a single point source, the angle with which it passes through the plane of the configurable collimator changes as the beam is moved away from the center of the field. For this reason, leaves may have curved edges, as shown in <figref idref="f0044">Fig. 46</figref>, so that the edges can always be placed a location that makes them tangent to the particle beam. In an example implementation of the configurable collimator, the tracks on which both primary and secondary carriages move are curved so that flat leaf edges can be used in lieu of curved leaf edges, and so that the flat but remain tangent to the particle beam.

0162To summarize, in some implementations, the configurable collimator may have a relatively small size, at least in part due to the linear motors described herein. Thus, in contrast to standard multi-leaf collimators, an example configurable collimator may therefore be used to trim a fraction of a treatment area at one time, e.g., an area that is less than the entire treatment area and that is about equal to one spot size, two spot sizes, three spot sizes, four spot sizes, five spot sizes, and so forth. Thus, in some implementations, the configurable collimator may be small enough to trim a single spot at once and may be large enough to trim several spots in one position, but not the entire field without moving. As noted, the ability to trim a single spot may be used to maintain a regular shape of a treatment column as the energy of the particle beam used to create that column varies.

0163The scanning system may include the configurable collimator described herein, which is placeable relative to the irradiation target to limit the extent of the particle beam and thereby limit the extent of the particle beam. For example, the configurable collimator may be placed in the beam path down-beam of the energy degrader and before the particle beam hits the treatment area of the irradiation target. The configurable collimator is controllable to allow the particle beam to pass therethrough and then hit certain parts of the treatment area, while preventing the particle beam from hitting other parts of the patient. <figref idref="f0048">Fig. 51</figref> depicts placement of an implementation of the configurable collimator 970 relative to a patient 971. The direction of beam 971a is also shown.

0164<figref idref="f0024">Figs. 26</figref> and <figref idref="f0025">27</figref> show parts an example of a proton therapy system 1082 containing a particle accelerator mounted on a gantry. Because the accelerator is mounted on the gantry it is in or adjacent to the treatment room. The particle accelerator may be the synchrocyclotron of <figref idref="f0003">Fig. 3</figref>; however, the system is not limited to use with synchrocyclotrons. The gantry and the particle accelerator may be controlled, along with the scanning system, to treat columns of an irradiation target using ultra-high dose rate radiation in the manner described herein. In some implementations, the gantry is steel and has two legs (not shown) mounted for rotation on two respective bearings that lie on opposite sides of a patient. The gantry may include a steel truss (not shown) that is connected to each of its legs, that is long enough to span a treatment area in which the patient lies, and that is attached at both ends to the rotating legs of the gantry. The particle accelerator may be supported by the steel truss for motion around the patient.

0165In the example of <figref idref="f0024">Figs. 26</figref> and <figref idref="f0025">27</figref>, the patient is located on a treatment couch 1084. In this example, treatment couch 1084 includes a platform that supports the patient. The platform also may include one or more restraints (not shown) for holding the patient in place and for keeping the patient substantially immobile during movement of the couch and during treatment. The platform may, or may not, be padded and/or have a shape (e.g., an indentation) that corresponds to the shape of part of the patient. The couch may be moved via arm 1085.

0166<figref idref="f0026">Fig. 28</figref> shows an example of the gantry configuration described in <patcit id="pcit0012" dnum="US7728311B"><text>U.S. Patent No. 7,728,311</text></patcit> incorporated herein by reference, and includes components of an alternative implementation of a proton therapy system that usable to treat columns of an irradiation target using ultra-high dose rate radiation in the manner described herein. The example proton therapy system of <figref idref="f0026">Fig 28</figref> includes an inner gantry 1190 having a nozzle 1191, a treatment couch 1192, and a particle accelerator 1193 (e.g., a synchrocyclotron of the type described herein) mounted on an outer gantry 1194 for rotation at least part-way around the patient to deliver radiation to target(s) in the patient. Treatment couch 1192 is controllable and configured to rotate and to translate the patient in the manner described herein.

0167In the example of <figref idref="f0026">Fig. 28</figref>, particle accelerator 1193 is also mounted to outer gantry 1194 also to enable linear movement (e.g., translational movement) of the particle accelerator in the directions of arrow 1195 along arms 1196. As also shown in <figref idref="f0026">Fig. 28</figref>, the particle accelerator 1193 may be connected to a gimbal 1199 for pivoting motion relative to the gantry. This pivoting motion may be used to position the accelerator, and thus the beam, for treatment.

0168Components of the scanning system including the scanning magnet, the ion chamber, the range modulator, and the collimator may be mounted on, in, or coupled to a nozzle 1081, 1191 of the proton therapy system's inner gantry. These components may be controlled by the control system to treat columns of an irradiation target using ultra-high dose rate radiation. In both examples, the nozzle is movable along a track of the inner gantry (1080 or 1190) relative to the patient and the particle accelerator, and is extensible towards, and retractable away from, the patient, thereby also extending and retracting the components mounted thereon.

0169In some implementations, the synchrocyclotron used in the proton therapy system described herein may be a variable-energy synchrocyclotron. In some implementations, a variable-energy synchrocyclotron is configured to vary the energy of the output particle beam by varying the magnetic field in which the particle beam is accelerated. For example, the current may be set to any one of multiple values to produce a corresponding magnetic field. In an example implementation, one or more sets of superconducting coils receives variable electrical current to produce a variable magnetic field in the cavity. In some examples, one set of coils receives a fixed electrical current, while one or more other sets of coils receives a variable current so that the total current received by the coil sets varies. In some implementations, all sets of coils are superconducting. In some implementations, some sets of coils, such as the set for the fixed electrical current, are superconducting, while other sets of coils, such as the one or more sets for the variable current, are non-superconducting (e.g., copper) coils.

0170Generally, in a variable-energy synchrocyclotron, the magnitude of the magnetic field is scalable with the magnitude of the electrical current. Adjusting the total electric current of the coils in a predetermined range can generate a magnetic field that varies in a corresponding, predetermined range. In some examples, a continuous adjustment of the electrical current can lead to a continuous variation of the magnetic field and a continuous variation of the output beam energy. Alternatively, when the electrical current applied to the coils is adjusted in a non-continuous, step-wise manner, the magnetic field and the output beam energy also varies accordingly in a non-continuous (step-wise) manner. The scaling of the magnetic field to the current can allow the variation of the beam energy to be carried out relatively precisely, thus reducing the need for an energy degrader. An example of a variable-energy synchrocyclotron that may be used in the particle therapy systems described herein is described in <patcit id="pcit0013" dnum="US9730308B"><text>U.S. Patent No. 9,730,308</text></patcit> entitled "Particle Accelerator That Produces Charged Particles Having Variable Energies", the contents of which are incorporated herein by reference.

0171In implementations of the particle therapy system that use a variable-energy synchrocyclotron, controlling the energy of the particle beam to treat a column of the target may be performed by changing the energy of the particle beam output by the synchrocyclotron. In such implementations, a range modulator may or may not be used. For example, controlling the energy of the particle beam may include setting the current in the synchrocyclotron main coils to one of multiple values, each which corresponds to a different energy at which the particle beam is output from the synchrocyclotron. A range modulator may be used along with a variable-energy synchrocyclotron to provide additional changes in energy, for, example, between discrete energy levels provided by the synchrocyclotron.

0172In some implementations, a particle accelerator other than a synchrocyclotron may be used in the particle therapy system described herein. For example, a cyclotron, a synchrotron, a linear accelerator, or the like may be substituted for the synchrocyclotron described herein. Although a rotational gantry has been described (e.g., the outer gantry), the example particle therapy systems described herein are not limited to use with rotational gantries. Rather, a particle accelerator may be mounted, as appropriate, on any type of robotic or other controllable mechanism(s) - characterized herein also as types of gantries - to implement movement of the particle accelerator. For example, the particle accelerator may be mounted on or more robotic arms to implement rotational, pivotal, and/or translational movement of the accelerator relative to the patient. In some implementations, the particle accelerator may be mounted on a track, and movement along the track may be computer-controlled. In this configuration, rotational and/or translational and/or pivotal movement of the accelerator relative to the patient can also be achieved through appropriate computer control. In some implementations, the particle accelerator may be stationary and located outside the treatment room, with the beam being delivered to a nozzle in the treatment room.

0173In some examples, as noted above, ultra-high dose rates of radiation may include doses of radiation that exceed 1 Gray-per-second for a duration of less than 500ms. In some examples, ultra-high dose rates of radiation may include doses of radiation that exceed 1 Gray-per-second for a duration that is between 10ms and 5s. In some examples, ultra-high dose rates of radiation may include doses of radiation that exceed 1 Gray-per-second for a duration that is less than 5s.

0174In some examples, ultra-high dose rates of radiation include doses of radiation that exceed one of the following doses for a duration of less than 500ms: 2 Gray-per-second, 3 Gray-per-second, 4 Gray-per-second, 5 Gray-per-second, 6 Gray-per-second, 7 Gray-per-second, 8 Gray-per-second, 9 Gray-per-second, 10 Gray-per-second, 11 Gray-per-second, 12 Gray-per-second, 13 Gray-per-second, 14 Gray-per-second, 15 Gray-per-second, 16 Gray-per-second, 17 Gray-per-second, 18 Gray-per-second, 19 Gray-per-second, 20 Gray-per-second, 30 Gray-per-second, 40 Gray-per-second, 50 Gray-per-second, 60 Gray-per-second, 70 Gray-per-second, 80 Gray-per-second, 90 Gray-per-second, or 100 Gray-per-second. In some examples, ultra-high dose rates of radiation include doses of radiation that exceed one of the following doses for a duration that is between 10ms and 5s: 2 Gray-per-second, 3 Gray-per-second, 4 Gray-per-second, 5 Gray-per-second, 6 Gray-per-second, 7 Gray-per-second, 8 Gray-per-second, 9 Gray-per-second, 10 Gray-per-second, 11 Gray-per-second, 12 Gray-per-second, 13 Gray-per-second, 14 Gray-per-second, 15 Gray-per-second, 16 Gray-per-second, 17 Gray-per-second, 18 Gray-per-second, 19 Gray-per-second, 20 Gray-per-second, 30 Gray-per-second, 40 Gray-per-second, 50 Gray-per-second, 60 Gray-per-second, 70 Gray-per-second, 80 Gray-per-second, 90 Gray-per-second, or 100 Gray-per-second. In some examples, ultra-high dose rates of radiation include doses of radiation that exceed one of the following doses for a duration that is less than 5s: 2 Gray-per-second, 3 Gray-per-second, 4 Gray-per-second, 5 Gray-per-second, 6 Gray-per-second, 7 Gray-per-second, 8 Gray-per-second, 9 Gray-per-second, 10 Gray-per-second, 11 Gray-per-second, 12 Gray-per-second, 13 Gray-per-second, 14 Gray-per-second, 15 Gray-per-second, 16 Gray-per-second, 17 Gray-per-second, 18 Gray-per-second, 19 Gray-per-second, 20 Gray-per-second, 30 Gray-per-second, 40 Gray-per-second, 50 Gray-per-second, 60 Gray-per-second, 70 Gray-per-second, 80 Gray-per-second, 90 Gray-per-second, or 100 Gray-per-second.

0175In some examples, ultra-high dose rates of radiation include doses of radiation that exceed one or more of the following doses for a duration of less than 500ms, for a duration that is between 10ms and 5s, or for a duration that is less than 5s: 100 Gray-per-second, 200 Gray-per-second, 300 Gray-per-second, 400 Gray-per-second, or 500 Gray-per-second.

0176In some examples, ultra-high dose rates of radiation include doses of radiation that are between 20 Gray-per-second and 100 Gray-per-second for a duration of less than 500ms. In some examples, ultra-high dose rates of radiation include doses of radiation that are between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10ms and 5s. In some examples, ultra-high dose rates of radiation include doses of radiation that are between 20 Gray-per-second and 100 Gray-per-second for a duration that is less than 5s. In some examples, ultra-high dose rate rates of radiation include doses of radiation that are between 40 Gray-per-second and 120 Gray-per-second for a time period such as less than 5s. Other examples of the time period are those provided above.

0177In some implementations, the size, the shape, or the size and shape of the holes in the collimators described herein may be changeable or otherwise configurable - for example, one or more of the hole or slot locations may be moved. For example, one or more of the holes or slots may be formed using fingers or leaves mounted on one or more carriages as described, for example, in <patcit id="pcit0014" dnum="US20170128746A"><text>U.S. Patent Application No. 2017/0128746</text></patcit> titled "Adaptive Aperture".

0178Operation of the example proton therapy systems described herein, and operation of all or some component thereof, can be controlled (as appropriate), at least in part, using one or more computer program products, e.g., one or more computer programs tangibly embodied in one or more non-transitory machine-readable media, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components.

0179A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a network.

0180Actions associated with controlling all or part of the operations of the example proton therapy systems described herein can be performed by one or more programmable processors executing one or more computer programs to perform the functions described herein. All or part of the operations can be controlled using special purpose logic circuitry, e.g., an FPGA (field programmable gate array) and/or an ASIC (application-specific integrated circuit).

0181Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only storage area or a random access storage area or both. Elements of a computer (including a server) include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from, or transfer data to, or both, one or more machine-readable storage media for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Non-transitory machine-readable storage media suitable for storing computer program instructions and data include all forms of non-volatile storage area, including by way of example, semiconductor storage area devices, e.g., EPROM, EEPROM, and flash storage area devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

0182Any two more of the foregoing implementations may be used in an appropriate combination with an appropriate particle accelerator (e.g., a synchrocyclotron). Likewise, individual features of any two more of the foregoing implementations may be used in an appropriate combination. Elements may be left out of the processes, systems, apparatus, etc., described herein without adversely affecting their operation. Various separate elements may be combined into one or more individual elements to perform the functions described herein.

0183Although the present invention is defined in the attached claims, it should be understood that the present invention can also (alternatively) be defined in accordance with the following embodiments: <ol id="ol0001"><li>1. A system comprising: <ul id="ul0002" list-style="none" compact="compact"><li>a particle accelerator to produce a particle beam to treat a patient;</li><li>a carrier comprising openings including a first opening and a second opening, the carrier comprising a material that inhibits transmission of the particle beam, and the carrier being located between the particle accelerator and the patient; and</li><li>a control system to control movement of the particle beam to the first opening to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first opening, and to control movement of the particle beam from the first opening to the second opening.</li></ul></li><li>2. The system of embodiment 1, wherein the openings comprise an array of holes, the first opening comprising a first hole and the second opening comprising a second hole.</li><li>3. The system of embodiment 1, wherein the openings comprise an array of slots, the first opening comprising a first slot and the second opening comprising a second slot.</li><li>4. The system of embodiment 1, further comprising: <ul id="ul0003" list-style="none" compact="compact"><li>an energy degrader between the particle accelerator and the patient, the energy degrader comprising structures configured to move into and out of path of the particle beam in order to change an energy of the particle beam;</li><li>wherein the control system is configured to control movements of the structures into or out of a path of the particle beam to change the energy of the particle beam.</li></ul></li><li>5. The system of embodiment 4, wherein the structures comprise plates for changing the energy of the particle beam as the particle beam passes through one or more of the plates, the plates comprising boron carbide.</li><li>6. The system of embodiment 1, wherein the particle accelerator comprises a superconducting magnet comprising conductive coils; and wherein the control system is configured to change a current through the conductive coils to change the energy of the particle beam.</li><li>7. The system of embodiment 1, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first opening, a columnar portion of a target in the patient before the particle beam moves from the first opening to the second opening; and wherein, while the particle beam is at the first opening, the particle beam delivers a dose of radiation to the target that exceeds one Gray-per-second for a duration of less than five seconds.</li><li>8. The system of embodiment 1, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first opening, a columnar portion of a target in the patient before the particle beam moves from the first opening to the second opening; and wherein, while the particle beam is at the first opening, the particle beam delivers a dose of radiation to the target that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds.</li><li>9. The system of embodiment 1, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first opening, a columnar portion of a target in the patient before the particle beam moves from the first opening to the second opening; and wherein, while the particle beam is at the first opening, the particle beam delivers a dose of radiation to the target that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.</li><li>10. The system of embodiment 1, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first opening, a columnar portion of a target in the patient before the particle beam moves from the first opening to the second opening; and wherein, while the particle beam is at the first opening, the particle beam delivers a dose of radiation to the target at an ultra-high dose rate.</li><li>11. The system of embodiment 1, wherein the openings comprise holes, the first opening comprising a first hole and the second opening comprising a second hole; and wherein controlling movement of the particle beam to the first hole and then to the second hole comprises centering the particle beam at first hole then centering the particle beam at the second hole.</li><li>12. The system of embodiment 1, wherein, following movement of the particle beam from the first opening to the second opening, the particle beam never again moves to the first opening.</li><li>13. The system of embodiment 1, further comprising: <ul id="ul0004" list-style="none" compact="compact"><li>a scanning magnet comprising conductive coils, the scanning magnet for generating a magnetic field to affect the movement of the particle beam;</li><li>wherein the control system is configured to control movement of the particle beam by changing a current through the conductive coils of the scanning magnet to affect the magnetic field.</li></ul></li><li>14. The system of embodiment 1, further comprising: <ul id="ul0005" list-style="none" compact="compact"><li>a track on which the carrier is mounted for movement within a beam field of the particle beam; and</li><li>a motor that is configured to move the carrier along the track.</li></ul></li><li>15. The system of embodiment 14, wherein the control system is configured to control the motor to move the carrier along the track based on movement of the particle beam.</li><li>16. The system of embodiment 1, further comprising: a ridge filter to spread-out a Bragg peak of the particle beam.</li><li>17. The system of embodiment 1, further comprising: <ul id="ul0006" list-style="none" compact="compact"><li>a track on which the carrier is mounted for movement; and</li><li>a motor that is configured to move the carrier along the track in response to one or more commands from the control system.</li></ul></li><li>18. The system of embodiment 1, wherein the control system is configured to change an energy of the particle beam while the particle beam remains stationary at the second opening, and to control movement of the particle beam from the second opening to multiple additional openings, with the particle beam remaining stationary for a period of time at each of the multiple additional openings while the energy of the particle beam changes.</li><li>19. A collimator comprising: <ul id="ul0007" list-style="none" compact="compact"><li>a carrier comprising one or more openings, the carrier comprising a material that inhibits transmission of a particle beam, each of the one or more openings having a size and a shape that are not changeable;</li><li>a track on which the carrier is mounted for movement within a beam field of the particle beam; and</li><li>a motor that is configured to move the carrier along the track based on movement of the particle beam.</li></ul></li><li>20. The collimator of embodiment 19, wherein the one or more openings comprises an array of holes.</li><li>21. The collimator of embodiment 19, wherein the one or more openings comprises a single linear array of holes.</li><li>22. The collimator of embodiment 19, wherein the one or more openings comprises one or more slots extending across a longitudinal dimension of the carrier.</li><li>23. The collimator of embodiment 19, wherein the one or more openings comprises a single slot extending across a longitudinal dimension of the carrier.</li><li>24. The collimator of embodiment 19, wherein the carrier comprises at least one of nickel, brass, or tungsten.</li><li>25. The collimator of embodiment 19, wherein the motor that is responsive to commands from a control system to move the carrier along the track.</li><li>26. The collimator of embodiment 19, wherein the carrier is a first carrier, wherein the collimator comprises a second carrier comprising an array of openings, wherein the second carrier comprises a material that inhibits transmission of a particle beam, and wherein the second carrier is mounted for movement within the beam field of the particle beam.</li><li>27. The collimator of embodiment 26, wherein the motor is configured also to move the second carrier along the track based on movement of the particle beam.</li><li>28. The collimator of embodiment 26, wherein the first carrier and the second carrier are connected to each other physically.</li><li>29. The collimator of embodiment 26, wherein the first carrier and the second carrier are configured for independent movement relative to each other.</li><li>30. The collimator of embodiment 26, wherein the motor is a first motor, and wherein the collimator further comprises a second motor configured to move the second carrier.</li><li>31. The collimator of embodiment 30, wherein the second motor is configured to move the second carrier based on the movement of the particle beam.</li><li>32. A system comprising: <ul id="ul0008" list-style="none" compact="compact"><li>a particle accelerator to produce a particle beam to treat a patient;</li><li>a carrier comprising an opening, the carrier comprising a material that inhibits transmission of the particle beam, and the carrier being located between the particle accelerator and the patient; and</li><li>a control system to control movement of the particle beam to a first part of the opening to enable at least part of the particle beam to reach the patient, to change an energy of the particle beam while the particle beam remains stationary at the first part of the opening, and to control movement of the particle beam from the first part of the opening to a second part of the opening.</li></ul></li><li>33. The system of embodiment 32, wherein the opening is a slot that extends along the carrier.</li><li>34. The system of embodiment 32, wherein the control system is configured to change an energy of the particle beam while the particle beam remains stationary at the second part of the opening, and to control movement of the particle beam from the second part of the opening to multiple additional parts of the opening, with the particle beam remaining stationary for a period of time at each of the multiple additional parts of the opening while the energy of the particle beam changes.</li><li>35. The system of embodiment 32, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first part of the opening, a columnar portion of a target in the patient before the particle beam moves from the first part of the opening to the second part of the opening; and wherein, while the particle beam is at the first part of the opening, the particle beam delivers a dose of radiation to the target that exceeds one Gray-per-second for a duration of less than five seconds.</li><li>36. The system of embodiment 32, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first part of the opening, a columnar portion of a target in the patient before the particle beam moves from the first part of the opening to the second part of the opening; and wherein, while the particle beam is at the first part of the opening, the particle beam delivers a dose of radiation to the target that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds.</li><li>37. The system of embodiment 32, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first part of the opening, a columnar portion of a target in the patient before the particle beam moves from the first part of the opening to the second part of the opening; and wherein, while the particle beam is at the first part of the opening, the particle beam delivers a dose of radiation to the target that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.</li><li>38. The system of embodiment 32, wherein the control system is configured to change the energy of the particle beam so that the particle beam treats, through the first part of the opening, a columnar portion of a target in the patient before the particle beam moves from the first part of the opening to the second part of the opening; and wherein, while the particle beam is at the first part of the opening, the particle beam delivers a dose of radiation to the target at an ultra-high dose rate.</li><li>39. The system of embodiment 32, further comprising: <ul id="ul0009" list-style="none" compact="compact"><li>an energy degrader between the particle accelerator and the patient, the energy degrader comprising structures configured to move into and out of path of the particle beam in order to change an energy of the particle beam;</li><li>wherein the control system is configured to control movements of the structures into or out of a path of the particle beam to change the energy of the particle beam.</li></ul></li><li>40. The system of embodiment 39, wherein the structures comprise plates for changing the energy of the particle beam as the particle beam passes through one or more of the plates, the plates comprising boron carbide.</li><li>41. The system of embodiment 32, wherein the particle accelerator comprises a superconducting magnet comprising conductive coils; and wherein the control system is configured to change a current through the conductive coils to change the energy of the particle beam.</li><li>42. The system of embodiment 32, further comprising: <ul id="ul0010" list-style="none" compact="compact"><li>a track on which the carrier is mounted for movement within a beam field of the particle beam; and</li><li>a motor that is configured to move the carrier along the track.</li></ul></li><li>43. A system comprising: <ul id="ul0011" list-style="none" compact="compact"><li>a particle accelerator to provide a particle beam to treat a patient located in a treatment room; and</li><li>an energy degrader comprising: <ul id="ul0012" list-style="none" compact="compact"><li>multiple structures, each structure of the multiple structures for changing an energy of the particle beam as the particle beam passes through the structure, each structure of the multiple structures comprising boron carbide; and actuators, each actuator for controlling movement of a corresponding one of the multiple structures into or out of a path of the particle beam;</li><li>wherein the energy degrader is located in the treatment room.</li></ul></li></ul></li><li>44. The system of embodiment 42, wherein each structure comprises a plate.</li><li>45. The system of embodiment 42, wherein each structure comprises a polyhedron.</li><li>46. The system of embodiment 42, wherein each structure is pure boron carbide.</li><li>47. The system of embodiment 42, wherein one or more of the multiple structures comprises a composite material comprised of boron carbide and graphite.</li><li>48. The system of embodiment 42, wherein the energy degrader is located no more than three meters from the patient along a beam line of the particle beam.</li><li>49. The system of embodiment 42, wherein the energy degrader is located no more than two meters from the patient along a beam line of the particle beam.</li><li>50. The system of embodiment 42, wherein the energy degrader is located no more than one meter from the patient along a beamline of the particle beam.</li><li>51. The system of embodiment 42, further comprising: <ul id="ul0013" list-style="none" compact="compact"><li>a scanning magnet to move the particle beam relative to the patient;</li><li>wherein the energy degrader is located between the scanning magnet and the patient.</li></ul></li><li>52. The system of embodiment 42, wherein the particle beam is applied to the patient at an ultra-high dose rate.</li><li>53. The system of embodiment 42, wherein the particle beam is applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds.</li><li>54. The system of embodiment 42, wherein the particle beam is applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds.</li><li>55. The system of embodiment 42, wherein the particle beam is applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.</li><li>56. The system of embodiment 42, wherein the structures are controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate.</li><li>57. The system of embodiment 42, wherein the actuators comprises linear motors.</li><li>58. A system comprising: <ul id="ul0014" list-style="none" compact="compact"><li>a particle accelerator to provide a particle beam to treat a patient located in a treatment room; and</li><li>an energy degrader comprising: <ul id="ul0015" list-style="none" compact="compact"><li>multiple structures, each structure of the multiple structures for changing an energy of the particle beam as the particle beam passes through the structure, each structure of the multiple structures comprising boron carbide; and actuators for controlling movement of the multiple structures into or out of a path of the particle beam;</li><li>wherein the energy degrader is located no more than four meters from the patient along a beamline of the particle beam.</li></ul></li></ul></li><li>59. The system of embodiment 58, wherein the structures are controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate.</li><li>60. The system of embodiment 58, wherein the energy degrader is located no more than three meters from the patient along a beam line of the particle beam.</li><li>61. The system of embodiment 58, wherein the energy degrader is located no more than two meters from the patient along a beam line of the particle beam.</li><li>62. The system of embodiment 58, wherein the energy degrader is located no more than one meter from the patient along a beamline of the particle beam.</li><li>63. The system of embodiment 58, wherein the particle beam is applied to the patient at an ultra-high dose rate.</li><li>64. The system of embodiment 58, wherein the particle beam is applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds.</li><li>65. The system of embodiment 58, wherein the particle beam is applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds.</li><li>66. The system of embodiment 58, wherein the particle beam is applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.</li><li>67. The system of embodiment 58, wherein the structures are controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient using an ultra-high dose rate.</li><li>68. The system of embodiment 58, wherein the actuators comprises linear motors.</li><li>69. The system of embodiment 58, wherein one or more of the multiple structures comprises a composite material comprised of boron carbide and graphite.</li><li>70. A system comprising: <ul id="ul0016" list-style="none" compact="compact"><li>a particle accelerator to provide a particle beam to treat a patient located in a treatment room;</li><li>a scanning magnet to move the particle beam relative to the patient; and an energy degrader comprising: <ul id="ul0017" list-style="none" compact="compact"><li>multiple structures, each structure of the multiple structures for changing an energy of the particle beam as the particle beam passes through the structure, each structure of the multiple structures comprising boron carbide; and actuators, each actuator for controlling movement of a corresponding one of the multiple structures into or out of a path of the particle beam;</li><li>wherein the energy degrader is located between the scanning magnet and the patient.</li></ul></li></ul></li><li>71. The system of embodiment 70, wherein the energy degrader is located no more than one meter from the patient along a beamline of the particle beam.</li><li>72. The system of embodiment 70, wherein the particle beam is applied to the patient at an ultra-high dose rate.</li><li>73. The system of embodiment 70, wherein the particle beam is applied to the patient at a dose rate that exceeds 1 Gray-per-second for a duration of less than 5 seconds.</li><li>74. The system of embodiment 70, wherein the particle beam is applied to the patient at a dose rate that is between 20 Gray-per-second and 100 Gray-per-second for a duration that is between 10 milliseconds and 5 seconds.</li><li>75. The system of embodiment 70, wherein the particle beam is applied to the patient at a dose rate that is between 40 Gray-per-second and 120 Gray-per-second for a duration of less than 5 seconds.</li><li>76. The system of embodiment 70, wherein the structures are controllable to move into or out of the particle beam while the particle beam remains stationary in order to treat a column of tissue within the patient at an ultra-high dose rate.</li><li>77. The system of embodiment 70, further comprising: an outer gantry on which the particle accelerator is mounted, the outer gantry being controllable to move the particle accelerator at least part-way around the patient.</li><li>78. The system of embodiment 77, further comprising: an inner gantry that is controllable to move in concert with the outer gantry, the inner gantry comprising a nozzle that is extendible towards, and retractable away from, the patient, the energy degrader being located in the nozzle.</li><li>79. The system of embodiment 78, wherein the energy degrader is located in a treatment room in which the particle beam is applied to the patient; and wherein the nozzle is retractable fully into the inner gantry.</li><li>80. The system of embodiment 70, wherein the particle beam has a spot size of less than 1.2 centimeters (cm) sigma for a particle beam having an energy of 70MeV or greater.</li><li>81. The system of embodiment 70, wherein the particle beam has a spot size of less than 1.2 centimeters (cm) sigma.</li><li>82. The system of embodiment 70, wherein the particle beam has a spot size of less than 0.5 centimeters (cm) sigma.</li><li>83. The system of embodiment 70, wherein there are no structures used to affect the particle beam between the energy degrader and the patient.</li><li>84. The system of embodiment 70, further comprising: a configurable collimator between the energy degrader and the patient, the configurable collimator being controllable to trim the particle beam at a resolution as small as a single spot.</li><li>85. The system of embodiment 70, wherein the actuators comprises linear motors.</li><li>86. The system of embodiment 70, wherein the actuators comprises rotary motors that each drive a corresponding linear actuator to control movement of a corresponding structure.</li><li>87. The system of embodiment 70, wherein one or more of the multiple structures comprises a composite material comprised of boron carbide and graphite.</li><li>88. The system of embodiment 70, wherein each of the multiple structures comprises pure boron carbide.</li></ol>