Adjustable collimator for radiation therapy

Nov. 8, 1960 d. t. green 2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Filed March 28, 1956 7 Sheets-Sheet 1

<img file="US2959680A_D0001.tif" />

Nov. 8, 1960

D. T. GREEN

2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Filed March 28, 1956

Sheets-Sheet 2

<img file="US2959680A_D0002.tif" />

Nov. 8, 1960 d. τ. green 2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY Filed March 28, 1956 7 Sheets-Sheet 3

<img file="US2959680A_D0003.tif" />

<img file="US2959680A_D0004.tif" />

Nov. 8, 1960 d. τ. green 2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY Filed March 28, 1956 7 Sheets-Sheet 4

<img file="US2959680A_D0005.tif" />

Nov. 8, 1960 d. τ. green 2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Filed March 28, 1956 ⁷ Sheets-Sheet 5

<img file="US2959680A_D0006.tif" />

<img file="US2959680A_D0007.tif" />

Nov. 8, 1960

D. T. GREEN

2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Filed March 28, 1956

Sheets-Sheet 6

<img file="US2959680A_D0008.tif" />

Nov. 8, 1960

D. T. GREEN

2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Filed March 28, 1956

Sheets-Sheet 7

<img file="US2959680A_D0009.tif" />

2,959,680

Patented Nov. 8, 1960

United States Patent Office

2,959,680

ADJUSTABLE COLLIMATOR FOR RADIATION THERAPY

Donald T. Green, Cleveland,, Ohio, assignor to Picker X-Ray Corporation, Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio

Filed Mar. 28,1956, Ser. No. 574,523

Claims. (CI. 250—105)

This invention relates to improvements in an adjustable collimator for high energy rays emanating from a source adapted for radiation therapy.

An object of the present invention is to provide means for controlling high energy rays of the type described by the use of a plurality of ray absorbing diaphragms, movably mounted and arranged progressively from the source outwardly, and mechanisms for holding the inner edges, nearest the rays, of correspondingly positioned diaphragms, on a given side of the beam, in relation progressively diverging away from the source to form a symmetrical beam about an axis through the source.

A further object of the present invention is to provide mechanisms for holding the inner edges of a plurality of diaphragms substantially aligned along the slanting sides of an imaginary cone or polygonal pyramid whose longitudinal axis is . through the source of high energy rays in all adjusted positions of the diaphragms, and more especially where the apex of said cone or pyramid is located approximately at said source.

A further object of the present invention is to provide an other-than-point source of high energy rays and to provide mechanisms for holding a series of movable diaphragms in various adjusted positions, and in each of these positions the inner edges of these diaphragms are substantially aligned along the slanting sides, of an imaginary cone or pyramid, the sides of which extend approximately through the lateral edges of the source.,

A further object of the present invention is to provide a plurality of ray absorbing diaphragms contained within an expandable housing with the change in shape of the housing capable of moving one or more of, the diaphragms in a preselected manner.

A further object of the present invention is to provide a plurality of ray absorbing diaphragm sets mounted in contact with each other to provide maximum ray absorption.

A further object of the present invention is to provide a plurality of ray absorbing diaphragm sets, slidably mounted in stacked relationship on each other and, more particularly, with an expandable frame for supporting said sets.

A further object of the present invention is to provide an adjustable collimator for. high energy rays, having ray absorbing diaphragms adapted to be moved to change the shape of the beam emanating from the. collimator, and having an indicator responsive to the positions of said diaphragms and actuated independent of the means for moving said diaphragms, whereby back, lash error is eliminated.

A further object of the present invention.is to provide a light source having a light beam coinciding with a beam of high energy rays and to provide crossed, cables in the center of , said beams for. locating by said light beam the center of said ray beam during use.

A further object of the present invention is to provide an adjustable collimator for high energy rays characterized by its structural simplicity, compactness of assem2 bly, efficient ray. absorption of stray rays, ease of opera·: tion, wide range of beam shapes, sharp definition of the edges of the beam, minimum size housing for a given beam size, and smoothly fashioned housing contour even 5 though the changing shape of the housing causes the changes in beam shape.

Other features of this invention reside in the arrangement and design of the parts for carrying out their appropriate functions.

Other objects and advantages of this invention will be apparent from the accompanying drawings and description and the essential features will be set forth in the appended claims.

In the drawings,

Fig. 1 is a side elevational view of the adjustable collimator of the present invention;

Fig. 2 is a bottom view taken along the line 2—2 of Fig. 1;

Fig. 3 is a vertical longitudinal sectional view taken 20 along the line 3—3 of Fig. 2;

Fig. 3a is an enlarged top plan view of a modified form of diaphragm;

Fig. 3 b is a vertical sectional view taken along the line 3b—3b of Fig. 3 a;

Fig. 4 is a horizontal sectional view taken along the line 4—4 of Fig. 3 inside the bottom cover, below the expandable frame for supporting the diaphragms, and below the crossed cables;

Fig. 5 is a horizontal sectional view taken along the 30 line 5—5 of Fig. 3 looking upwardly at the bottom most diaphragms, of the pile supported by the adjustable frame;

Fig. 6 is a horizontal sectional view taken along the line 6—6 of Fig. 3;

Fig. 7 is a bottom view similar to Fig. 4 but with the ³⁵ diaphragms in the expanded position shown in Fig. 8;

Fig. 8 is a vertical sectional view taken along the line 8—8 of Fig. 7 across corners of the collimator;

Fig. 9 is a horizontal sectional view taken along the line 9—9 of Fig. 8;

⁴⁰ Fig. 9a is a horizontal sectional view, similar to Fig. 9, of a modified form of corner member and spring attachment;

Fig. 10 is a vertical sectional view taken generally along the line 10—10 of Fig. 3 with parts omitted , for 45 clarity and other parts partially cut away;

Fig. 11 is a vertical sectional view taken generally along the line 11—11 of Fig. .3 with portions thereof partially cut away and with parts omitted for clarity;

Fig. 12 is a sectional view taken along the line 12—12 of Fig. 11; while

Figs. 13 and 14 are pictorial representations of the shape and size ranges of high energy fay beams that may be achieved by adjustment of the collimator of the presently disclosed embodiment of my invention with Figs.¹13 55 and 14 respectively disclosing the size ranges of, beams of square and rectangular transverse cross sections.

Before the apparatus here illustrated is specifically described, it is to be understood that the invention here involved is not limited to the structural details or ar00 rangement of parts here shown since adjustable collimators embodying the present invention may .take various forms. It also is to be understood that the phraseology or terminology herein employed is for purposes of description and not! of limitation since the scope of the ⁶⁵ present invention is denoted by the appended claims.

' The use of high energy rays in medicine, industry and research has posed problems for the control of these rays where a directed beam of the rays is required. The present invention is directed to this problem. Wherever 70 in the specification and claims the term “high energy rays” is used, or the equivalent, it is intended to include X-rays in the two to three niillion volt region, rays

2,959,680 from Cobalt⁶⁰, gamma rays or rays of a similar character or more penetrating than that. The present invention is described in connection with a Cobalt⁶⁰ source.

The invention will be described with respect to the use of the rays from a therapeutic point of view for treating human beings, although it will be understood that the invention is useful for controlling high energy rays for any use whatever.

The mounting and control of the source forms no part of the present invention except insofar as it provides a fixed primary aperture in combination with the adjustable secondary aperture or opening in the collimator of the present invention. Any suitable mounting and control may be provided, such as disclosed in the copending U.S. patent application filed by Harold E. Johns and John A. MacKay on May 18, 1954, Serial No. 430,584, now U.S. Patent No. 2,844,736, entitled “Collimator for High Energy X-Ray Beam.”

The high energy ray source in the present disclosure is a plurality of cobalt discs 20. The diameter of these discs is a matter of compromise. It is a question of balancing the disadvantages of a large source with the economic advantages in a large source of low specific activity. A source between one and three centimeters in diameter seems to be a suitable compromise with these two considerations in mind. This is the basis for the use of the phrase “other-than-point source” hereinafter mentioned.

Although the adjustable collimator is disclosed as forming the rays into a beam of square or rectangular transverse cross section, they may be formed into a beam having any desired shape in transverse cross section with a closed perimeter. The shape obtained would depend upon the shape of the beam defining surfaces, the number of diaphragms, and the arrangement of the diaphragms in the collimator.

The description hereinafter will be directed toward describing in detail the adjustable collimator for forming into a beam high energy rays emanating from the source 20 with this beam taking any desired shape or size, depending upon the characteristics of the collamator.

A mounting is provided for the collimator to connect it to the source and to permit rotation of the collimator about a vertical central axis in Fig. 3 extending longitudinally of the ray beam. Here, source 20 is in a shield 21 consisting of a mass of encasing lead, tungsten alloy or other heavy metal surrounded by a steel case 22. A bearing ring 24 is secured to case 22 by a plurality of circumferentially spaced screws 25. A main collimator bearing ring 26 has an auxiliary ring 27 secured thereto by screws 28 to form the inner half of the cylindrical raceway for ball bearings 29. Naturally, rings 24, 26 and 27 are all generally annular in shape so that collimator main ring 26 may be rotated about its central axis and concentric with respect to the source 20. Collimator main ring 26 is secured to a collimator base sleeve 31 in Figs. 3 and 6 by a plurality of circumferentially spaced screws 33. Collinator base 32, secured in any suitable manner within the bore of the base sleeve 31, such as by bolts (not shown), is formed of an upper base portion 32a, preferably formed of dense material such as tungsten alloy to provide a fixed aperture and to control leakage radiation outside the collimator, secured to a lower base portion 32b by screws 32c and having a central conical bore 32d to permit downward passage of the rays from the source 20.

The collimator includes the collimator base 32 and the structure described hereinafter in detail. It has a plurality of spaced diaphragm sets, here shown as 6½ sets but of any satisfactory number, arranged in pile formation in 13 layers along, and at right angles to, the axis of the beam. The extra half set is provided to give the desired dimensions and operating characteristics in the specifically illustrated construction.

Each set is composed of a plurality (here shown as four) of L-shaped, ray absorbing movable diaphragms 35, 36, 37 and 38 in Figs. 3, 5, 7 and 8. Diaphragms 35 and 36 are located in one plane or zone extending transverse to the beam axis while diaphragms 37 and 38 are located in an adjacent plane or zone. In each plane, the L-shaped diaphragms are nested together to form a pair, so that when they are assembled in the manner shown in Fig. 5, they fit together to leave a square opening in the center thereof.

Since each diaphragm is substantially identical, only diaphragm 35 in Fig. 5 will be described in detail. This diaphragm has two legs 35α and 35b joined at a vertex with leg 35α being shorter so as to form the horizontal leg of the L-shape, as viewed in Fig. 5. These legs respectively have inner, beam-defining edges 35c and 35d for forming the rays emanating from the source 20 into a ray beam. Diaphragm 35 at the upper left in Fig. 3 is formed of joined layers consisting of an inner lead plate 35e having stainless steel facing plates 35/ on top and bottom surfaces thereof. Also, at the vertex, a vertically extending through sleeve 35g (Figs. 5 and 8) is located, preferably being of brass material.

A modified form of diaphragm is shown in Figs. 3α and 3b at 135, which may be substituted for the diaphragms in the bottom four layers in Fig. 3. It has tungsten alloy inserts 135p, 135? mounted by screws and forming beam defining edges 135c, 135d. Tungsten, being dense, sharpens the penumbra of the beam. Facing plates 135/ may have bearing portions 135/' bent over the outer edge of the inner lead plate to serve as a bearing surface for relative movement with the inside surface of the surrounding housing. Similar bearing portions may be formed by bent extensions of plates 35/ in Fig. 3, if so desired.

In each set, the four diaphragms 35 to 38 are arranged so that they are progressively displaced 90 degrees about the axis of the beam; note diaphragms 35, 37, 36 and 38 in Fig. 5. However, this so-called progressive displacement need not be in immediately following or clockwise order, as illustrated. It should be readily apparent that the number of diaphragms in each set, the shape of the opening 40 defined by the inner edges thereof, and the shape of the diaphragms (other than L-shape) may be a matter of choice; and that diaphragms may be arranged to define an opening with any type closed perimeter capable of forming, by the inner edges thereof, the source rays into a ray beam.

Since there are four diaphragms in each set, there are four diaphragm groups with each group having correspondingly positioned diaphragms, such as one group with all the diaphragms 35, a second group with all of the diaphragms 36, etc.

The collimator is provided with interconnected operating mechanisms for moving the diaphragms between the positions shown in Figs. 3 and 8. In the illustrated form, there are four operating mechanisms, interconnected by base 32, with each mechanism operatively connected with correspondingly positioned diaphragms in each set forming one of the four diaphragm groups. Each mechanism adjusts all of the correspondingly positioned diaphragms in its group simultaneously, and adjustment of all four operating mechanisms will move or adjust all of the diaphragms.

Collimator base 32 has a housing supported thereby and hanging therefrom for enclosing and supporting the diaphragms 35, 36, 37 and 38. This housing has four sides generally forming a square prism in Fig. 3 and expandable into generally a square pyramid in Fig. 8 while maintaining an unbroken enclosure on its periphery for the diaphragms. The diaphragms are constrained to move with the walls of the housing so that the shape of the housing will determine the shape of the beam opening 40. See Figs. 3, 8, 13 and 14.

In the present disclosure, the housing includes in Fig. 5 a plurality of housing side wall members 41, 42, 43

2,959,680 &amp; and ,44jpivotally connected ;at 41α, 42α, 43a_;.and,44a, in. Figs.. 1,- 3 and.! 5 : to. .base.. 32: to permit relative pivotal movement. The hinge center lines of these pivots in the present construction define a . square, but may within the scope of this invention define any other rectangle, whose sides are parallel to the sides of the ray beam forming opening 40 of the .diaphragms with the square lying in a plane perpendicular to the beam axis, centered on the beam axis, and located as near the source 20 as practicable so that the inner edges of the diaphragms will line, up well with the edges of source 20. Since each side wall member has basically the same construction, only side wall member 43 will be described in detail. Side wall member 43 has an arm 436 in Fig. 3 having pivot pin 43α at its upper end and secured at its lower end to a side wall formed by an outer plate 43c and an inner plate 43 d secured together and maintained in spaced relationship by a plurality of spacers 43e and screws 43/.

A plurality of corner members (here shown as four in number) 51, 52, 53 and_; 54 operatively connect adjacent· side wall members to complete the formation of the housing in Fig. 5 around the diaphragm sets. Each corner member is .an angle member with the. planar walls thereof, operatively connected to.move, respectively in the planes of the. adjacent side wall members. Since each corner member is identical, only the corner member.51. will be described in detail. It includes two angularly disposed plates 51α and 51b connected together by. a corner forming connecting. portion. 51c. The operative connection between corner-member 51and the adjacent side wall members 41 aiid,42 is provided by haying plate 51α telescoped,into ‘the. space, between plates 41c and 41d and having plate 51b telescoped into the space between plates 42c and 42&lt;/. The contacting side walls, of these plates are machined flat so that the corner members and side wall members may move telescopically relative to each other between the Fig. 3 and 8 positions in the manner shown in Fig. 11 by the dotted, and full line positions.

Although four side, wall members and four corner members are. illustrated, it should be readily understood , that any desired number may be assembled together to form a housing depending upon the mode of operation of the collimator desired and the shape of the ray beam forming Opening 40.

Means are provided for operatively connecting a group of correspondingly positioned diaphragms to the vertex of each corner member so that the diaphragms are constrained to follow the movement of the housing, during expansion and contraction thereof. This is shown in Fig. 5 by having all diaphragms 35 connected to corner member 51, diaphragms 38 to corner member 52, diaphragms. 36 to corner member 53, and diaphragms 37 to corner member 54. At each corner, a connecting construction is provided including control bars 61, 62, 63 and 64. Since each is identical, only control bar 61 in Fig. 8 will be described. Control bar 61 includes tie bar or cylindrical rod 61α having stop pin 616 adjacent at least its lower end and a plurality of spherical beads 61c and spacers 61d alternately arranged in telescopic relation over tie bar 61α with pin 61b preventing telescopic disassembly. Each of the beads 61c, preferably formed of brass or other bearing material, has a generally spherical peripheral surface to form the inner member of a universal joint connection. Every other one of these beads 61c is located in one of the diaphragm sleeves 35g, while the remainder are located in spacer and spring holder sleeves 66. ’ A spring 67 in Fig. 9 is wrapped around each sleeve 66 and has its opposite ends com nected to the connecting portion 51c of the corner member 51;. Hence, the control bar 61, extending through aligned holes in the group of correspondingly positioned diaphragms 35, is resiliently pulled by the springs 67 toward the corner member 51 so as to constrain the dia6 phragms.35.to, follow,the,movement of the corner mem-: ber 5Ϊ&lt;· Hence, the outer edges of diaphragm legs 35a and; 356 in Fig. 5 are pulled respectively against the innersurfaces of side wall member plates 42d and 41d so that the orientation and location of ray defining edges 35d and 35c of opening 40 in each diaphragm 35: is determined-by. the side walls 41 and 42.

As an alternate construction, control bar 61 may be of one piece construction with a periphery resembling thatof beads 61c and spacers 61d.

Drive means is provided for causing relative movement between side wall and corner members. This drive means is shown most clearly in Figs. 3, 6, 10, 11 and 12. Two drive units are provided; one actuated by turning knob 70 in Fig. 3 is adapted to move side wall members 41 and 43 in and out and the, other actuated by turning knob 71 to . move. side . wall , members 42 and 44in and out. Each drive unit is substantially identical so only one will be described, namely, the one, controlled by knob 71.. Knob 71 drives a shaft 71α in Fig, 3 having a pinion 72 thereon in Fig. 10 rotatably carried in side wall member 41. Pinion .72 meshes with and drives, gear 73 which in.turn, drives gear 74, carrying respectively pinions 73α and. 74α, all rotatably mounted in side wall member 41. In Fig. 11, the corner member ' plates 51a and 54a have sector gears 75 and 76 respec-. tively secured thereto and adapted to be driven by pinions 74α and 73α respectively. Back-up rollers 77 and 78 keep the racks engaged against their respective pinions with these rollers rotatably carried by side wall member 41. In the opposite side wall member 43 in Fig. 3 are located similar gears, pinions, sector gears and back-up rollers with the drive between them being provided through gears 73; 79, 80 and 81 in Fig. 11; gear 81, universal joint 82, cross shaft 83, universal joint 84 rind gear 85 in Fig.' 6; and gears 85, 86 and 87 in Fig. 3. ...... . .

A similar gearing and drive construction is provided between control knob 70 and side wall members 41 and 4.3.

Hence, one pair of opposite side wall members, such as 42 and 44, may be swung in or out by knob 71 independently of the other side wall members 41 and 43 to contract or.expand the ray beam forming opening 40 in only one dimension, such as dimension A m Fig. 5. The other'dimension B is controlled'by knob 70. Rotation of gears 73 and 74 in Fig. 11 will drive corner member plates 51α and 546 either into or out of their' respective side wall member 41. By properly correlating and phasing movements of’ control knobs 70 and 71, the housing may be changed in shape from a square prism in Fig. 3 to either a square or rectangular pyramid so as to obtain all the different beam shapes shown in Figs. 13 and 14. It should be noted that after a pair of these opposite side walls are properly assembled equidistant from the longitudinal central axis of the beam, the teeth of gears 73, 73α, 74,: 74α, 75 and 76 will maintain this equidistant relationship.

The weight of all of these diaphragms 35, 36, 37 and 38 is slidably supported by an expandable frame when the ray beam is directed downwardly from the source 20 in the manner shown in the drawings. The frame is probably best shown in Figs. 3, 5, 7 and 8. Four bottom frame comers 91, 92, 93 and 94 are provided with four pairs of bottom frame guide rods 95 and 96 telescopical-, ly connected in aligned holes in adjacent comers to permit the expansion thereof. Between each pair of adjacent comers, a hinge construction is provided. These four hinges have respectively upper leaves 101,- 102, 103 and 104 pivotally connected by hinge pins 105 to lower leaves .97, 98, 99 and 100., The upper leaves serve as the spacer between the inner and outer plates of the respective side wall members 41, 42, 43 and 44, while the lower leaves are bottom frame supports with each rigidly secured to one pair of guide rods 95 and 96. Therefore,

2,959,680 as the side wall members and corner members move outwardly from the Fig. 3 to the Fig. 8 position, the bottom frame comers 91 to 94 move from the Fig· 4 position in contact with the bottom frame supports 97 to 100 outwardly to the Fig. 7 position by telescoping over their associated guide rods 95 and 96. The expandable frame is rigidly carried by the side wall members and is centrally located with respect thereto by means of bottom frame supports 97-100 and their respective guide rods 95 and 96. The bottom frame comers 91-94 provide support for the lower ends of the control bars 61-64 and for the diaphragms 35-38.

A bottom cover for the collimator is provided by four cover plates 111, 112, 113 and 114 of identical construction, as shown in Figs. 1 and 2. For example, plate 111 has a bottom wall Illa and a turned-up side flange 1116, as shown in Fig. 1. These plates 111, 112, 113 and 114 are secured respectively by screws to bottom frame supports 97, 98, 99 and 100 in Fig. 7 so that the space between them always corresponds with the proper opening 40 for the ray beam because these cover plates will move in and out with the expandable frame.

It has been found that a suitable design is obtained with the present construction with the following dimensions. The treatment distance from source 20 to the skin is about 40 centimeters while the lower end of the collimator, designated by cover plates 111-114, is approximately 25 centimeters from the source 20. The range of field sizes formed by opening 40 is from 4x4 cm. square to 15 x 15 cm. square. Also, any rectangle having either dimension between 4 and 15 cm. is obtainable. Of course, collimators of this design for other field sizes and treatment distances could be easily produced. Any field size, (square, rectangular, or any other suitable shape) may be. obtained. The stack of diaphragms 35-38 is formed in thirteen layers with each being one-half inch thick and each diaphragm having overall dimensions of 4% by 2%·, inches. The stack is 6½ inches high. When the collimator diaphragms are in the Fig. 3 and Fig. 5 position, prismatic beam C in Fig. 13 is produced. When they are expanded into the Fig. 7 and 8 position, a beam of square pyramid form D in Fig. 13 is produced with the slope of the pyramid sides equal to the slope of the side wall members 41-44 of the housing. In this pyramid form, the sides and edges of the pyramid (the edges being shown by lines DI and D2 in Fig. 8) run through the lateral edges of the source 20 in the manner shown in Fig. 8. This is especially true when an other-than-point source 20 .is used. It should be noted that the sides of the prism in Fig. 3 also extend through the lateral edges of the source in a similar manner. This is also true of the intermediate adjusted positions of the collimator.

This construction provides good shielding from stray rays emanating from source 20 and also provides a collimator of compact overall length along the axis of the beam. It should be noted that at least some portions of the diaphragms in each set overlap in every adjusted position, including the maximum spread apart position in Fig. 7. These diaphragms not only overlap along the axial length of the beam but also are in contact with the axially adjacent diaphragms to provide a dense relationship to reduce leakage. The inner edges of the diaphragms form opening 40 with a closed perimeter for forming the rays emanating from the source into a ray beam. The overall height, or length along the axis of the beam, of the stack of diaphragms 35-38 remains constant during adjustment between the Fig. 3 and 8 positions because the diaphragms slide one upon the other and the expandable frame supporting them at the bottom is pivotally connected by hinge pins 105 to the side wall members.

The diaphragm sets are slidably mounted and supported by the adjustable frame. Each set is slidably supported by its adjacent sets with the sets arranged in layers along the length of the beam. Each diaphragm has stainless steel facing plates, such as plates 35/, on top and bottom so that sliding of the layers takes place at the junction of the steel surfaces with minimum friction and minimum wear while the lead plate center section, such as 35e, provides maximum ray absorption. Frame corners 91-94 have sufficient contact with the terminal edges of the diaphragms to support their weight even in the expanded position of Fig. 8.

When the diaphragms are in the fully expanded position of Fig. 7 or Fig. 8, it is desirable to provide spacers located axially between the diaphragms along the length of the beam to support correspondingly positioned diaphragms in different layers. As the diaphragms move outwardly, voids are created in other places than in the central opening 40; note Fig. 7. Two different type spacers are provided to give proper support.

First, sleeves 66 around the control bars 61, 62, 63 and 64 serve not only as spring holder sleeves but also as spacer sleeves since the axial dimension of each is equal to the thickness of the transversely aligned diaphragm adjacent thereto. These spacer sleeves 66 are provided in two opposite corners of each layer and in all four corners in each diaphragm set. Each spacer remains in the same relative position to its associated corner of the housing for the different collimator adjustment sizes between the Fig. 3 and Fig. 8 positions. They thus maintain the proper spacing between the diaphragm in the expanded position of Fig. 8 that is provided by the diaphragms themselves in the fully closed position shown in Figs. 3 and 5. Each L-shaped diaphragm has a notch, such as notch 35/ in diaphragm 35, cut out of the outer surface of its longer leg to provide clearance for the associated spacer when the collimator is fully closed.

Second, the short leg of each L-shaped diaphragm⁵helps support and maintain the spacing between the long legs of the adjacent diaphragms. Note how short leg 35α in Fig. 7 helps support long 386 of diaphragm 38 in the fully expanded position of Fig. 7. Also, the inner edge of this short leg forms a portion of the wall of the opening 40 in all positions of adjustment and is always less than or equal to the dimension of the opening 40 parallel -thereto. Compare dimension B in Fig. 5 with the horizontal dimension of the largest square opening 40 in Fig. 7.

The edges of the beam are sharply defined in all positions. of adjustment. This is true because all portions of the inner edges of each L-shaped diaphragm forming the ray beam lie in a plane perpendicular to the axis of the beam in every position of adjustment. Hence, the edges of the beam will be sharply defined on a flat target arranged perpendicular to the beam axis. If some of the portions of a beam defining straight edge were in different planes, the beam edge formed thereby would be fuzzy instead of sharp.

L-shaped diaphragms normally do not lend themselves to .form both rectangular and square beams because of adjustment problems. However, in the present construction, one dimension of rectangular beam opening 40 may be changed while another dimension remains constant. Also, the illustrated construction permits adjusting each diaphragm in two different perpendicular directions both lying in a. common plane transverse to the beam axis.

Two different types of corner member constructions are illustrated in Figs. 9 and 9α. The basic difference between the two is in the connecting portion 51c or 151c. Connecting portion 51c forms a hinge along the vertex of the corner or along the edge of the pyramid formed by the housing. Hinge plate 51α has a generally cylindrical socket end 51al wrapped around a cylindrical pivot pin end 5161 formed on hinge plate 516. Hence, this construction permits relative movement of the walls 51α and 516 not only pivotally about the longitudinal hinge axis of end 5161 but also along the longitudinal hinge axis, if such last mentioned movement is required during the change in shape of the housing. An inwardly

2,959,680

9ί directed lug. 51a2 .is formed on the .periphery of the, socket portion-extending .along.,.the. .length .of.-the. hingean:. Fig'. 8 and having holes to receive the'ends of the springs 67 so as to urge the control bar 61, 62,:63 or 64 into the corner-formed by its associated hinge.

One or more of the comer-members may be of solid construction if no relative movement, either hinge pivotal movement or axial relative movement along the hinge axis, is required. In Fig. 9α, the': corner: member is formed of flat plate stock having a slot 151d milled along the length thereof. Then, the plate is folded along the length of the slot to form the plates 151α and 1515 corresponding respectively to plates 51α and 51b -in Fig.: 9The slot 151d has made the folding operation easier and more accurately performed. The slot, having also had its side walls folded inwardly, forms a dovetail slot or groove running along the length of and inside the vertex of the corner member. A slide member, taking the form of the head of a rivet 152 in the present disclosure, is slidably retained in the groove 151d for travel along the length of the groove if necessary. The opposite ends of each spring 67 are adapted to be detachably secured to one of the rivets 152 so that the spring 67 will pull its associated diaphragm into the vertex of the corner-member. This corner member 151 is of rigid angular formation so that its construction is much simpler than the corner member shown in Fig. 9. With the Fig. 9α construction, the centers of curvature of the sector gears 75 and 76 in Fig. 11, and those in the other three housing wall members, preferably coincide with the hinge axes of pivot pins 41α-44α so that relative movement between the hinge plates 151α and 151b is not necessary during adjustment of the housing between the Fig. 3 and Fig. 8 positions.

However, the hinge construction in .Fig. 9 does not necessarily need this coincidence of the pivot axes and. the centers of curvature of the. sector, gears since relative movement is. possible between the hinge plates in two different directions.

Alternate constructions within the scope of the present invention readily suggest themselves. First, in Fig. 5, inner plate 51α is carried by corner member 51; while straddling plates 41c and 41 &lt;7are carried by. side wall member 41. However, corner member 51 may be formed with the straddling plates while side wall, member 41 has the single intermediate plate, if so desired, Second, in Fig. 5, correspondingly positioned diaphragms 35 are connected to corner member 51, 38 to 52, 36; to 53 arid 37 to 54. However, correspondingly positioned diaphragms may be connected with one of their associated side walls instead of a corner member. This is especially true if the diaphragms have a straight single beam defining edge instead of being L-shaped.

Indicators are provided for registering the size of the opening 49-independently of the gear type driving or operating mechanisms shown in Fig, 11. Here, two identical indicator constructions are provided, one for the housing side wall members controlled by knob 71 and the other for those controlled by knob 79. Since these indicator constructions are identical, only one is shown in detail and will be described in detail. Adjacent knob 71 in Fig. 10 is the Indicator. 120, for. registering movement of side wall members 41 and 43 by control knob 79. Indicator 120 has an indicia bearing disk 121, .in Figs. 3 and 10 with a series of numbers thereon and is adapted to rotate about a central, shaft carried by side wall, member 41, which is carried with the ray beam. defining inner. edges 35d of correspondingly positioned diaphragms 35. The. indicia is adapted to align, with a 'scale·, on the edge of an. opening 122 in side wall member 41,upon rotation of the disk 121. A cable. 123 jri. Fig.. 3 is ^wrapped, around a drum. 121α coaxially carried.by the disk 121in Fig. 3,. extends downwardly, about an idler pulley 124 rotatably, mounted on a pivot pin' 105 mi iFigs. 3 and, 7, extends across the center of the ray beam opening 40, is anchored at the.other end in a horseshoe shaped locking nut, 125.. around the. opposite hinge: pin 105::'and'held, in place by the bottom cover plate 113. A spiral spring 126 is fixed at opposite ends to the side wall member 41 and the cable drum so as to rotate the indicator disk 121 :and to wind up the cable 123 on the/drum until all slack is eliminated from the cable. Since'anchoring nut 125 is carried by the opposite side wall member 43, its position will be a function of the inner ray beam defining edge of · diaphragm 36. Therefore, the reading on indicator 121 in window 122 will be a function of the dimension B in Fig. 5 of ray beam opening 49.: In similar manner, the dimension A in Fig. 5 will be shown by its indicator operatively connected to the cable 123' in a similar manner in Fig. 7. These indicators will register the size of the opening 40. independently of the gear drives in Fig. 11 so as to eliminate, any back lash error that may occur during movement of the housing between the different adjusted positions.

These crossed cables in Fig. 7 serve another function. The cables Ϊ23 and 123' always cross the center of the path of the beam through the opening 49 at the end of the collimator most remote from the source 29 (at the bottom in Fig. 3) because each cable is positioned centrally with respect to the opposite side wall members 41 and 43 or 42 and 44 by its associated pulley 124 and nut 125. In Fig. 3, a light source 139 is provided in the base 32 adjacent the ray source 29 for providing with the help of mirror 131, extending across base opening 32(7, a downwardly extending light beam through the opening 40 coinciding with the high energy ray beam. If the light source 130 throws downwardly a light beam during use of the high energy ray beam, the shadow cast upon the target by the crossed cables 123 and 123' will indicate the center of the ray beam to aid in its usage. The cross defined will be sharply defined since the cables are fairly' near the target arid remote from the light source 130.

Various changes in details and arrangement of parts can be made by one skilled in the art without departirig from either the spirit of this^; invention or the scope of the appended claims.