Patent GB-792683-A (GB)
Title: An improved apparatus for utilising the emanations from radio-active sources for medical therapy and other purposes
Inventor: STEIN STEPHEN
IPC: G21F5/02
Filed: 1955-10-21
Abstract: 792,683. Containers for radio-active sources. NUCLEAR ENGINEERING, Ltd. Oct. 15, 1956 [Oct. 21, 1955], No. 30100/55. Class 98(1) A container for radio-active sources of radiation consists of a main body for containing and shielding a source, an applicator head into which the source may be moved to produce a beam of radiation of a required cross-section in a required direction, a shielded conduit through which the source passes from the main body to the applicator head and vice versa, a shutter in the body for closing the conduit, and operating mechanism mounted on the main body to open the shutter and feed the source from the main body to the applicator head and vice versa. As shown in Figs. 1, 2 and 3, the main body 1 of the apparatus consists of a mass 4 of heavy metal enclosed in a steel shell 5. The body 1 is supported .by bearings 6 formed at opposite sides and engaged by two spigots 7 which form part of a supporting structure (not shown). An electrically controlled mechanism 8 is mounted on the flattened rear end 1a of the body, and a neck 3 supporting an applicator 2 is mounted on a flattened front end 1b. The main body encloses a cylindrical chamber 10, its axis parallel to the trunnion axis, and a insert 12 formed with two parallel circular 'bores 13. At their rear ends, the bores 13 are restricted to flat slots 14, and at opposite sides of the bores 13 grooves 15 are formed in continuation with the slots 14. Each bore 13 receives a radio-active source 16 mounted at the end of a carrier rod 17 which is connected to a flat perforated metal tape 18 by which the rod may be moved. and which passes through a slot 14 into the driving mechanism 8 and into guides 19 on the outside of the main body. As the rod 17 moves forward, the opposite edges of the tape 18 slide in and are supported by the grooves 15 in the bore 13. Mounted side by side in chamber 10 are two heavy metal discs 26, each rigidly secured to a pin 27 journalled in bearing 28 in the side wall of chamber 10. Balls 29 placed between the discs allow them to rotate independently. Each disc has a diametrical bore 13a with opposed grooves 15a, which form in one position of the disc, continuations of bore 13 and grooves 15. The bores and grooves are also continued through an insert 25 in front of the chamber 10, and a dish-shaped element 30 bolted to the flattened front end 1b of the main body. 'The neck 3 is pivoted at 31 to the dish shaped element 30, the extent of its rotation being limited by a flange 33 thereon engaging a flange on the element 30. In each extreme position of the neck, one of a pair of micro switches 34 mounted on the element 30 is actuated. The neck 3 consists of a mass of heavy metal enclosed in a shell, and formed with a longitudinal bore 35 with diametrically opposite grooves 36. By rocking the neck about the pivot pin 31. the bore 35 with its grooves 36 can be brought into align ment with either of the bores 13 with their grooves 15 in the inserts 12 and 25. Grooves 36 are wider than grooves 15 to provide continuity between the two in both positions of the neck. An applicator head 2 is rotatably mounted on the rear end of neck 3, and may be clamped in any desired position by a screw clamp 44. It contains a bore 45 arranged in prolongation with the bore 35 in the neck 3 and terminating at the inner ends of two outwardly tapering ports 46, 47. A heavy metal plug 49 or an applicator 48 may be placed selectively in the ports 46, 47, and their insertion closes micro switches 51. A pointer or the like mounted on the applicator head facilitates the correct alignment. When the sources 16 are not in use, they are housed in the centre of the heavy metal mass 4, which normally consists of lead. The insert 12 may be of tungsten, and is shaped as shown to afford extra protection to compensate for the effect of the flattening of the front of the mass 4. Also, the discs 26 have central portions of tungsten, so that when the discs are turned at right angles to the bore 13 the sources are effectively shielded from the front. The insert 25, neck 3 and applicator 2 also preferably consist of tungsten alloy, the other heavy metal shielding being of lead. Rotation of the discs 26 is effected by means of rods 60 which slide in the central section of the body 1 on opposite sides of the cylindrical chamber 10, each rod 60 carrying a pin 61, Fig. 2a, which engages a wheel 62 fast with the pin 27 carrying the respective disc 26. Wheel 62 has flats 63 formed thereon at right angles to each other with a radial slot 64 between them. Each rod 60 is cut away in the vicinity of pin 61 so that, except when the wheel 62 is over the cutaway, it is prevented from rotating. When, however, the pin 61 engages slot 64 the cut-away portion of the rod 60 enables the wheel 62 to be turned through ninety degrees after which a flat thereon will again engage the rod 60. The driving mechanism 8 is mounted on a base plate 70, (see also Fig. 5). bolted to the flat ends 1a of the main body, and includes a stalling electric motor 71, the output shaft 72 of which engages a shaft 74 through reduction gear 73. Mounted on this shaft are two electric clutches 75, 76, through which drive may be imparted to two drums 77, 78, only one clutch being egaged at a time. A spring 79 inside each drum 77, 78 becomes wound up as the drum is rotated so that if the drive through the operative clutch is released the drum will be turned by the spring back to its starting position. Each drum 77, 78 is formed circumferentially with teeth 80 which engage in the apertures in one of the metal tapes 18. Each clutch also imparts drive through a gear train 81 to a wheel 82 in which is formed a cam 83 (see particularly Fig. 3). Cam 83 is engaged by a stud 84 on an arm 85 pivoted at one end to a bracket 86, the other end being linked to the end of one of the rods 60. The initial rotation of the wheel 82 lifts the stud 84 and causes arm 85 to be pivoted, thus exerting a pull on the rod 60. After its initial rotation, wheel 82 effects no further movement of rod 60, as the stud 84 simply rides round its periphery. On rotation of wheel 82 in the opposite direction, the stud 84 will engage a finger 88 on cam 83, which pushes the rod 60 back into its initial position. The parts of the driving mechanism are duplicated to provide independent operative movements for each radio-active source and disc 26. Each radio-active source and its disc are moved simultaneously, but the 'source is positioned a little behind the disc, which is rotated to a position wherein it accepts the source before the source has arrived at the entrance to chamber 10. As each source reaches its operative position in the. applicator head, a mechanical stop prevents further movement and causes the motor to stall and hold the source in position. Micro-switches in the guides 19 for the tapes illuminate tell-tale lights to indicate when the radio-active source moved by the tape has been moved into its witharawn or operative position. The circuit to each electric clutch includes one of the micro-switches 34, so that rocking the neck into either of its positions automatically ensures that drive will only be imparted to the radio-active source in the bore 13, aligned with the bore in the neck. The circuit to both clutches includes the micro-switch 51 on the applicator head, so that drive cannot be effected through either clutch unless the closure plug and applicator have been inserted in the applicator head. Should the spring return drive fail, the motor 71 may be reversed in order to withdraw a radio-active source from its position of use to the centre of the main body. Should the failure of the spring be followed by a failure of the motor, the source can be withdrawn by means of handwheels 91 (Fig. 6, not shown). The apparatus may be pivoted in a yoke carried at the lower end of a telescopic tube mounted on the ceiling of a treatment room, the apparatus and telescopic tube being counterweighted and driven by electric motors. Angular scales may be provided on all relatively rotatable parts, and adjustable contacts may limit the orientation of the applicator head. Exposure of a radio-active source may be effected from a remote control panel including indicator lamps, an exposure timer, a start button, an emergency stop button, an audible end of exposure signal, and a clock. Indicator lamps may also be provided on the treatment chamber door.