Patent Number: 043705553
Section: description

Referring now to the drawings, FIG. 1 shows an irradiation device which may advantageously be used in radiotherapy. This apparatus comprises a fixed support 1, an arm 2 movable about an axis X--X, an irradiation device 3 removably mounted on the mobile arm 2, a precollimator 13 and a secondary collimation device 4 of axis Y--Y. The collimator 4 is removably fixed on the mobile arm 2 by means of a support plate 15 fixed by screws 16. FIG. 2 shows a transverse section through the irradiation device 3 of FIG. 1. This irradiation device comprises a bowl-shaped container 5 provided with a flange 6. This container 5 may be removably fixed on the arm 2 by means of screws passing through said flange 6. A fixed shielding 7 for biological protection is placed inside the container 5. The shielding 7 at least partly surrounds a biological protection disc 8 rotatable about an axis passing through its centre C. The disc 8 is provided with a housing 9 adapted to receive a radioactive source. This housing 9 opens outwardly of the disc 8 so as to allow the beam of photons delivered by the radioactive source 10 to pass. The fixed shielding 7 is composed of a block 7a of depleted uranium, embedded in a block 7b of lead. The block 7a of depleted uranium surrounds the source of photons when the latter is in storage position shown in dashed and dotted lines in FIG. 2. The capacity of the uranium to absorb the radiation being about twice that of lead, the use of a block of depleted uranium ensures a satisfactory biological protection, whilst reducing the weight and size of the irradiation device according to the invention. In the embodiment shown in FIG. 2, an optical fibre 11, adapted to transmit a light flux, is disposed in the disc 8. The optical fibre 11 opens at one of its ends 11a, so-called receiver end, opposite a light source 12 fixed outside the container 5 and at its other end 11b, called emitter and, along axis Y--Y. Each of the receiver and emitter ends is held via means for adjusting their positioning. The optical device 12 focuses a ray of light on the receiver end of the optical fibre 11, this optical device 12 consisting for example of a light source associated with a reflector for focusing its light beam. Light ray should be understood in the present specification to mean an electromagnetic radiation in the visible part of the spectrum. The passage provided in the disc 8 for the optical fibre 11 is substantially rectilinear in shape, except for its ends. The emitter and receiver ends of the fibre 11 preferably determine an angle at the centre equal to 90.degree.. Such an arrangement renders the irradiation of the optical fibre in the course of functioning of the apparatus minimum. In FIG. 2, .alpha. designates the angle of rotation of the disc 8 which makes it possible to pass from the position of irradiation of the radioactive source 10 shown in solid lines, to the storage position of this same source, shown in dashed and dotted lines. The value of this angle .alpha. is 110.degree.. This value makes it possible to limit the rate of radiation leaks when the radioactive source 10 is in storage position, as well as the height of the biological protection body 7 surrounding the disc 8. FIG. 3 shows a longitudinal section through the irradiation device shown in FIG. 2. This view particularly shows the positionings of the disc 8 ensuring a rapid alternance of the positions of irradiation and of storage, with locking of the disc in position of irradiation and return thereof into storage position in case of a safety action or an electrical failure. The disc 8, mounted on bearings 15, rotates with the shaft 16. A clutch disc 18 is mounted at the end of the shaft 16. A pinion 20, mounted to rotate freely on the shaft 16, may be coupled to this shaft by means of the electromagnetic clutch 22. When the electromagnetic clutch 22 is supplied, the shaft 16 is rotated by the pinion 24 of the gear-down motor 26. On the other hand, the shaft 16 rotates, for example by means of a keying, with a pinion 30 driving a rack 32 which is intended to define the positions of irradiation and of storage of the disc 8. Also shown schematically in dashed and dotted lines is the mobile arm 2 on which the device of the invention is mounted, as well as the device for maintaining the position of the disc 8, designated by reference 36 and, finally, the device 38 for displaying the position of the disc. These devices will be described in greater detail with reference to FIGS. 4, 5 and 6. FIG. 4a shows a view in the direction of arrow IV of FIG. 3 of the device shown therein. This Figure particularly shows the device 41 for detecting the position of the disc 8. The rack 32 may be displaced by a gear-down motor between a first position, shown in solid lines in FIG. 4a, for which it is in abutment against an electro-magnetic suction member 36 whose position is adjustable by means of a nut 39, and a second position, shown in dashed and dotted lines in FIG. 4a, for which the rack 32 is in the vicinity of a buffer unit 40 whose action is adjusted by the positioning of rod 42. An electrical contact 41 controls the stoppage of the electro-magnetic clutch 22, when the rack 32, by being displaced in the direction of arrow f, comes to a short distance from the electro-magnetic member 36. Furthermore, to allow the disc 8 to return automatically into storage position, a spring 44 is interposed between a wall of the rack 32 and a fixed wall fast with the container 5, so that the disc automatically passes in the direction of arrow F from the position of irradiation to the position of storage if a safety device is triggered off or if there is an electrical failure. A second electrical contact 46 actuated by finger 45 enables the end-of-stroke position of the rack 32 when it is in the vicinity of the buffer device 40 to be determined. Finally, a third electrical contact 48 enables the beginning of irradiation to be determined. In fact, the beginning of irradiation is determined by the moment when the radioactive source 10 begins to appear in the precollimator. This position of the source, designated by reference 10a, has been shown in FIG. 4b. Finally, FIG. 4a shows in dashed and dotted lines a second position 10b of the radioactive source, which corresponds to the radioactive source 10 going slightly beyond the position of the axis Y--Y of the collimation device. The purpose of this arrangement is to allow compensation of the inevitable clearance of the rack and drive pinion. In FIG. 4b, reference 5 represents the precollimation device with, in addition, shown in dashed and dotted lines, a secondary collimation device 50 associated with the irradiation head. FIGS. 5 and 6 show in detail the system allowing the return by force of the disc 8 in the case of incident. This device, generally designated by reference 38, is composed of a dog 60 made fast with the shaft 16 by means of a keying. The dog 60 bears a dog finger 62. The rotation of the dog 60 is limited by two stops 64 and 66. The stop 64, which is made of rubber, corresponds to irradiation position. The stop 66 corresponds to the position of storage of the radioactive source 10. Furthermore, a disc 68 is fast with the dog 60. The disc 68 comprises coloured zones corresponding to the different positions of the disc. Zone 68a corresponding to storage position is green and zone 68c corresponding to the position of irradiation is red. A lever 70, whose angular movement is limited, is idly mounted on the end of the shaft 16. This lever allows the control by force of the disc 8 by means of the dog 60. It will be noted that the shaft 16 can be driven by this device only in one direction, this direction corresponding to the passage from the position of irradiation to the position of storage. FIG. 5 shows in dashed and dotted lines the positions 70a and 70b of the lever 70 which correspond respectively to the positions of irradiation and of storage. An outer indexing means 72 located opposite the disc 68 makes it possible to determine the position of this disc due to the coloured zones thereof. The irradiation device which has just been described has the important advantage of also serving as radioprotection cask for transporting the radioactive source. This makes it possible to adjust the source in the factory, at the moment of manufacture and to change the radioactive source simply, without calling upon specialised man-power. To this end, an irradiation device provided with a previously adjusted new source, ready for use, is transported to the site of use, the irradiation device acting as a radioprotection cask.