US2836729A - Beam therapy diaphragm - Google Patents

Description

4 May 27, 1958 J. L. sNARR Erm. 2,836,729

BEAM THERAPY DIAPHRAGM Filed Sept. 24, 1956 5 Sheets-Sheet l \\L\ x/f l 51:1 -I -A 7 19 ,o

May 27, 1958 J. l.. sNARR ErAL BEAM THERAPY DIAPHRAGM 5 Sheets-Sheet 2 Filed Sept. 24, 1956 Jaz-5;

ZW .4592 A? May27, 1958 J. l.. sNARR ETAL 2,836,729

1 BEAM THERAPY DIAPrmAGM Filed Sept. 24. 1956 5 Sheets-Sheet 3 May 27, 1958 1. L. sNARR Erm. 2,836,729

BEAM THERAPY DIAPHRAGM Filed Sept. 24. 1956 5 Sheets-Sheet 4 May 27, 1958 J. L. sNARR ET AL BEAM-THERAPY DIAPHRAGM 5 Sheets-Sheet 5 Filed Sept. 24', 1956 United States Patent O BEAM rI"HERAPY DIAPHRAGM .lames L. Snarr and Mervyn G. Brown, Ottawa,` Ontario,

Canada, assignors to Atomic Energy of Canada, Limited, Ottawa, Ontario, Canada, a corporation` ot' Canada Application September 24, 1956, Serial No. 611,656

Claims priority, application Canada July 18, 1956 Claims. (Cl. Z50-105) This invention relates to a collimator and more particularly to a collimator for defining a beam of radiation.

ln Canadian Patent 514,793, issued July 19, 1955, for an invention of Donald T. Green and Clifford S. Mc- Colm a collimating unit was described in which the beam of radiation was defined by two pairs of blocks movable ina unitary plane which was substantially perpendicular to the axis of the beam of radiation. One end of `each of the blocks was in abutment with the side of another block and the blocks of each pair were movable towards and away from each other. This enabled asquare or rectangular aperture to be defined by a collimator which occupied little space and gave adequate shielding against radiation from the source of the beam of radiation. The structure described in Canadian Patent 514,793 suffered however from the disadvantage that the aperture` had to be in the shape of a four sided figure. Where for example a cancerous growth is being treated it frequently is desirable that the aperture be shaped otherwise than square or rectangularly so as to enable the beam of radiation to conform to the shape of the growth being treated. This enables the beam to be concentrated on the growth being treated without over exposing healthy tissues.

The object of this invention is to provide an i m proved collimating unit in `which at least one and preferably each corner of the basic rectangularly shaped aperture can be cut off to a desired extent thus giving an increased choice of aperture contour. Where each corner can independently be out off, the aperture can be square, rectangular, five, six, seven or eight sides. Since the extent to which the corners can be cut oi varies a wide variety of aperture shapes can be provided.` Furthermore an equilateral eight sided figure will closely approximate a circle.

The foregoing object is accomplished by obliquely dividing one of said blocks and preferably each of said blocks along a line extending to the inner face"` ofthe last mentioned block at a point adjacent to the abutment of an end of said block with the side of another block to separate said last mentioned block into two segments.

`One of the segments is advanced or retracted with respect to the other while maintaining sliding engagement.` The advancement of said one segment progressively cuts olf a corner of the aperture While laterally displacing th other segment.

in the drawings which illustrate the preferred embodiment of this invention:

Figure 1 is an elevation view illustrating a diaphragm of the assembly shown in Figures l and 2.

up ICC Figure 4 is a sectional view `along the line IV`IV of Figure 3.

Figure 5 is` a sectional View. along the line V-V of Figure 3.

. Figure 6 is a perspective view partially broken away of the diaphragm section.

Figure 7 is a detail sectional view on theline Vll--Vll of Figure 3. A

Figure 8 is a sectional view on the line VIII-VIII of Figure 7.

Figure 9 is a top plan view of the diaphragm portion of the assembly shown in Figure l illustrating one of the auxiliary segments in an advanced position.

Referring now to the drawings. Figures l and 2. A diaphragm or collimating section 10 is connected by a light system containing unit 11 to a head 12 containing a suitably shielded source (no shown) of radiation. Head 12 can be similar to `the corresponding portion ofthe unit illustrated in Canadian Patent 514,793. Light system containing unit 11 includes a light switch 13 to control lights contained in housings 14. Light system containing unit 11 can also include afield angulation lock ing knob 15 which in one` position permits the entire diaphragm assembly 10 to be rotated about a vertical axis `with respect to Figurefl and in another position locks diaphragm 10. Since the light system containing unit and the treatment head do not form a part ofthis invention, they will not further be described.

The diaphragm unit 10 is shown in detail in Figures `3` to 8 inclusive and comprises an annularly shaped housing 16 at the upper edge of which is mounted a pair of segment shaped fixed guide plates 17 and 18. The inneredge 19 of Vfixed guide plate 1'7 is parallel to the inner edge 20 of fixed guide plate 18. A pair of moving guide plates 21 and22 are slidably mounted with respect to edges 19 and 20 by means of tongue and groove joints 22. Moving guide plates 21 and 22 each havegrooves 23 and 24 respectively to receive a pair of spaced rollers 25 mounted on a collimating block 26. Similarly groove 24 receives rollers 27 mounted on collimating block 28. Moving guide plate 21 moves inwardly andoutwardly with block 26 but rollers 25 permit block `26 tornove laterally with respect to -moving guide plate 21. Similarly block 28 moves inwardly and outwardly with moving guide plate 22 but can be displaced laterally with respect thereto. Blocks 26 and 2S have inner surfaces 29 and 30 which are parallel to each other. Block 26 has an end surface 31 which is at right angles to surface 29 and similarly block 2S has an end surface 32 at right angles to surface 30. A second` pair of blocks is provided by blocks 33 and 34. Block 33 has an inner surface 35 abutted byend surface 31 of block 26 and an end surface 36 at right angles to surface 35 and abutting inner surface 30 of block 28. Block 34 has an inner surface 37 abutted by end surface 32 of block 28 and has an end surface 39 at right angles to surface 37 and abutting inner surface 2,9.

Blocks 26, 2S, 33 and 34 are disposed in a unitary plane and are mounted so that each block is .capable of lateral movement. towards or away from each other, blocks 33 and 34 are displaced laterally. Similarly when blocks33 and 34 are 36, 32 and 37 and 29 and 39 to permit slidable lateral movement of each block with respectto the block which abuts its inner surfacefwhile maintaining abutment between the blocks. For this purpose the inner surfaceiof each of the blocks is provided with a groove 40 engaged by a tongue 41`on the abutting end surfaces.

The blocks are mounted on an upper cam plate When blocks 26 and 28 are moved` fWe claim: 1: In' acuimator blocks movable `in-a unitary*` planeA substantially perpen-` dicular to the axis of the beam ofradiation to define an cam plate 42 is artes with toners 4s and 4s Waimea` gage grooves `and 46 respectively in blocks 26 and 28. Upper cam plate 42 includes a'peripheral rack 47 engaged bypinion 48.. `Pinion 4S is controlled by upper cam plate turning knob 49. When upper cam plate` turn ing knob 49yis turned, cam plate 42 is rotated and rollers 43 and 44 cause` blocks 26 and 28 to be moved `towards or away fromeach other depending on Vthe direction of Arotationfof knob.49. Lowercam plate 50 is provided with rollers 5,1 and 52 which engage groove 5? in block 34 and groove 54 in block 33.` Lower cam plate 5t) has a peripheral rack 55 controlled by pinion 56 and lower cam plate turning knob 57. Rotation of knob 57 moves blocks 33 andf34 towards or away from eachother depending onthe directionof rotation. `The rollers or cam' bearings 43,` 44,` 51 and 52 should be mounted on in-V wardly directed ears such" as ears `53 and 59.Y This prevents the cam,plate`s .from encroaching on the beam emitting aperture and `also permits the rollers mounted on the lowerfcam plateto-operate blocks 34 and 35 withcomprises a main` segment ,66, and anrauxiliary segment 67. The auxiliary and main segments are each wedge shaped. Auxiliary eld'adjusting `knob 68 can be rotated to advance auxiliary segment 61 with respect to main segment of Yblock 26. This progressively cuts off ment 65 with respect tomain segment 6ft Auxiliary field adjusting knob advances auxiliary `segment 63 with d *a aperture for the emission of the beam, said blocks `comprising two pairs of blocks, the `blocks `of each of said pairs being on opposite sides of said aperture, each of said blocks having one end abutted against the side of one block of the other pair of blocks and having its inner faceabutted by the other block of the other pair `of blocks, means for maintaining the blocks in abutment as aforesaid, mountingimeans for said blocks permitting movement of said blocks within said unitary plane both in the direction of and in a lateral .direction with respect to said aperture, means for increasing` or decreasing the distance between one of said pairs of blocks,

means `for increasing or decreasing the distance between the other of said pairs of blocks, at least one of said blocks being obliquely divided along a line extending to the inner face of the la'stmentioned block at a point adjacent to the abutment of an end of said block with the side of another block to separate said last mentioned jblockinto two segments, means maintaining said segments in slidable engagement and meansfor advancing or retracting one ofsaid segmentswith respect to the other of said segments to change the shape of said aperture.

. 2. A collimator asin claim four blocks of the collimator is divided into two segments.

3. A` collimator as in claim 2 inlwhich themeans for Y advancing or retracting one ofV the segments of` each the corner between blocks 26 and 3x3.V Similarly auxiliary eld adjusting knob 69 advances or retracts auxiliary segrespect to main segment 62 and auxiliary field adjusting knob 71 advances auxiliary segment 66 with Vrespect to main segment 67. As each auxiliary segment isad-` vanced its associated main segment is displaced laterally. This lateral `displacement is permitted by the sliding en gagement between tongue 41 and groove ii)` and .by the sliding engagement;` between the cam plate roller ,which controls` the main segment in question 'and the cam plate roller engaging groove ofthe last mentioned mainse'gment.

The manner in which the auxiliary iield `adjusting knobs operate toadvance or withdraw the auxiliary seg'- ments is further illustrated in `Figures 7 and 8 with respect to the operation of auxiliary field adjusting knob 71. Auxiliary field adjusting knob 7l is'mounted una shaft 72 which carries, a screwthreaded member 73. Shaft 72 and its associated screw threaded member '73 are mounted on main segment` 66 by end bearing 74 and collar 75. A bearing member 76 threadably engaging screw threaded member 73 is mounted on auxiliary segment 67. When auxiliary iield adjusting knob 7l is turned auxiliary segment 67 is advanced with respect to main segment 66. s The main segment 66 and auxiliary segment 67 are slidablyinterlocked by a tongue 77 projecting from main segment 66 and engaging a groove 73 in auxiliary segment167y A slot 79 is provided in casing `16"toxaccommodate shaft 72 at diiferent positions lof block 34.` 1

Figure9 further illustrates thezrnanner in which vancing `thefauxiliary segments adjusts the Vshape of the aperture. In Figure 9, auxiliarysegment 6l `is, shown in an advanced position to define a five-sided aperture. Main segment 60 has been displaced by the advancing of auxiliary segment 6 1. Y

forudeiining'a beam of radiation,

. .block is operable independently of the means forY advancing or retracting the other blocks whereby segments can be adjusted to define the aperture in the shape of `a gure having from four to eight inclusive sides.

4. A collimator as in claim 3 in whichthemeans for advancing or `retracting one of the segments `ot each block comprises rotatable screw means extending `along the juxtaposed sides of the segments forming a block, said rotatable screw means` being journalled on one of said segments and threadably engaging 'the other of said segments so that rotation of said rotatable `screw means advances or retracts one of said segments with respect to the other.

5. In a collimator for defining. a beam `of radiation eight wedge shaped shielding members disposed and movable in a unitary plane to define a collimating aperture, said wedge shaped members being `arranged in pairs ,comprising a main wedge shaped member andV :anauxiliary wedge shaped member, the `wedge shaped members Vot" each pair `being arranged so `that one `wedge `defining side `of the marin wedge shaped member is juxtaposed to one wedge `defining side of the auxiliary wedge shaped member and the second wedge defining side of the main wedge shaped ,member extends at right angles to the Secondwedge defining side* of the` 'auxiliary` Wedge `shaped member, said second wedge deiining side of the aux'- iliary` Wedge shaped member being juxtaposed tothe second wedge defining side of the mainwedge shaped member of another pair of wedge shaped members, means for moving each pair of` wedge shaped members nwardlyor outwardly as a unit` to decrease'and enlarge respectively said aperture, mounting means for eachpair of wedge shaped members topermit one pair of said e wedge shaped members to be'displaced` `laterally each or withdrawing said `auxiliary wedge Shaped vmember relatively to saidmain wedge shaped member while maintaining one sideof each of the last mentioned wedge shaped members juxtaposed, the advancement of said auxiliary wedge shaped member "acting to displace its` main wedge shaped 4memberlaterally and `progressively References Cited in the iile ofn this patent` l' i UNITED STATES `PATENTS` Y 2,675,486

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