Patent GB-832373-A (GB)
Title: Adjustable beam limiting diaphragm for radiation therapy
IPC: G21K1/04
Filed: 1957-03-12
Abstract: 832,373. X-ray and like apparatus. PICKER X-RAY CORPORATION, WAITE MANUFACTURING DIVISION Inc. March 12, 1957 [March 28, 1956], No. 8076/57. Class 98(1) A beam limiting diaphragm consists of a number of sets of diaphragm plates arranged in a pile of constant length along the beam, each set consisting of L- shaped plates defining a beam limiting opening with a closed perimeter, and mechanisms connected with the plates for relative adjustment thereof. As shown in Fig. 3, the source of radiation, consisting of a number of discs 20 of radio-active cobalt, is enclosed in a shield 21 of lead or other heavy metals, surrounded by a steel case 22. A ring 26 carrying the diaphragm is rotatably mounted in a bearing ring 24 fixed to the casing 22. The base of the diaphragm assembly consists of two parts 32a, 32b bolted together and having a central conical opening 32d to allow the passage of radiation from the source 20. The diaphragm plates are L-shaped and arranged in sets of four each set consisting of a pair of plates 35, 36 adjustable towards and away from each other in one direction, and a pair of plates 37, 38 adjustable towards and away from each other in a direction at right angles, the arrangement of plates being as shown in Figs. 3 and 5. The plates are of lead, have stainless steel facing plates and sleeves 35g of brass located in one corner, and may also have tugnsten inserts let in along the beam-defining edges. The diaphragm plates are thus capable, on displacement, of providing a beam of square or rectangular cross-section of varying size. By altering the shape and number of the plates, a beam cross-section of any desired shape or size may be obtained. The housing for the diaphragm plates consists of five wall members 41, 42, 43, 44 pivotally connected at 41a, 42a, 43a, 44a, to the base 32. As shown in Fig. 3, the side wall 43 consists of inner and outer plates 43c, 43d held together by screws 43f and spaced apart by spacers 43e. The side member is fixed to an arm 43b hinged at 43a to the base 32. The other side walls are similarly constructed. The side walls are connected together by corner members 51, 52, 53, 54, as shown in Fig. 5. The member 51, for example, consists of two plates 51a, 51b connected together by a connecting portion 51c. Plate 51a slides in the space between the plates 41c, 41d of the side wall 41 and plate 51b slides in the space between plates 42c, 42d of side wall 42. One diaphragm plate of each set of four is connected to each of the corner members. As shown in Fig. 8, a control bar 61 consists of a rod 61a having threaded theron spherical beads 61c and spacers 61d, and is passed through the corners of the plates 35 so that the spherical beads 61c are alternatively located in the diaphragm plate 35g and in spacers 66. Each space 66 is encircled by a spring 67 fixed to the corner member 51, so that all the plates 35 move with the corner member 51. The other sets of diaphragm plates are similarly caused to move with the other corner members. The side wall members are caused to swing inwards and outwards in pairs by means of knobs 70, 71. As shown in Figs. 3, 10 and 11, knob 71 is connected to a pinion 72 which meshes with a gear 73 which in turn drives a gear 74, carrying respectively pinions 73a, 74a. The corner member plates 51b, 54a have sector gears 73, 76 which are driven by the pinions 74a, 73a respectively. Back-up rollers 77, 78 keep the sector gears engaged with the pinions. This mechanism, which is carried on the side wall 41, is connected to similar mechanism on the side wall 43 through gears 73, 79, 80, 81 (Fig. 11), connected by universal joints and a cross shaft to similar gearing of the side wall 43. Rotation of the knob 71 therefore moves the corner members 51, 54 towards and away from each other, and therefore controls the movement of side walls 42, 44. In a similar manner, movement of control knob 70 controls the relative movement of side wall members 41, 43. The movement of the corner members also causes relative movement of the diaphragm plates to adjust the shape and size of the beam cross-section. The weight on the diaphragm plate is supported by a frame consisting of four bottom frame corners 91, 92, 93, 94 (Fig. 7), connected by four pairs of bottom frame guide rods 95, 96 sliding telescopically in aligned bores in the corner pieces. Between each pair of corner pieces hinges are provided of which the lower leaves 97, 98, 99, 100 are each connected to one pair of guide rods 95, 96, and of which the upper leaves 101, 102, 103, 104 serve as spacers between the inner and outer plates of the side wall members. The bottom of the housing is covered by four overlapping plates, of which one pair 111, 113 are shown in Fig. 3. The aperture dimension controlled by the knob 71 may be indicated by means of a disc 121, (see Figs. 3 and 10), mounted on the side wall 41 and bearing a scale readable through an opening 122. A cable 123 is wrapped around a drum 121a (Fig. 3), connected to the disc 121 and extends downwardly about an idler pulley 124 mounted on the pivot pin 105 of the hinge 97, 101 (see also Fig. 7), and extends across the beam opening and is anchored to a horse-shoe shaped locking nut 125 mounted on the pin 105 of the opposite hinge. A spiral spring 126 keeps the cable in tension. Similar mechanism indicates the aperture controlled by the knob 70. The cables cross at the centre of the beam opening. A lamp 130, Fig. 3. and a mirror 131 throw a beam of light along the beam limiting opening so as to cast a shadow of the cables on the body to be irradiated to indicate the centre of the beam. Specification 815,118 is referred to.