Patent Number: 043705553
Section: summary

The present invention relates to a device for storing a source of .gamma. photons and for irradiating a body by the radiation from said source. The device is applicable to human and veterinary therapy, to metrology, biology, particularly in research, to medicine and to veterinary research. The invention also relates to a process for transporting and replacing a radioactive source in an irradiation device. More precisely, the invention relates to a device of the type comprising a body for biological protection, a disc element for supporting a source of photons, movable in said body between a first position allowing the source to be stored under good conditions of biological protection and a second position allowing a beam of photons to be emitted outside the body, a pre-collimator for limiting the beam to a given zone of the irradiated body. For certain applications, such as for example telecobaltotherapy, the device according to the invention further comprises an optical assembly for producing a light beam simulating the beam of photons and a secondary collimation device. Devices of the above-mentioned type, designed prior to the present invention, are known, which comprise an element for supporting a source of photons, which is mobile in translation, and an optical assembly constituted by a source of light, such as a light bulb, which is carried by the source-supporting element. U.S. Pat. No. 2,951,162 particularly discloses devices which comprise a metal shell offering biological protection against the radiation of a radioactive source, inside which is located a cylinder rotating about its longitudinal axis. This cylinder comprises two diametrically opposite longitudinal holes. The radioactive source is mounted on a removable bar acting as biological protection and engaging in one of said longitudinal holes. A light source mounted on a similar bar engages in the second longitudinal hole. The protective shell comprises a conical opening for the passage of the radiation from the source and that of the light beam. Such known devices present a certain number of drawbacks. In particular, they are heavy and of relatively large dimensions. This leads to an unbalance which is undesirable in the case of certain applications for which the irradiation device is subjected to a movement of rotation, such as the therapeutic treatment of a patient by irradiation of part of his/her organism. Another drawback of the known irradiation devices lies in the necessity to have access to the interior of the apparatus in order to change the light source or the radioactive source. Finally, the irradiation apparatus of known type, using radioactive sources, have another important drawback--these radioactive sources must be changed when they have lost a determined quantity of their activity, in the course of time. In particular, when these apparatus are used in radiotherapy, their use must be suspended and a specialised team must be called upon to change these sources in situ with suitable equipment. In addition, for certain applications such as the therapeutic treatment of a patient, a beam of photons of precise dimensions must be produced and the position of this beam must be adjusted. The irradiation devices of known type, which comprise an optical system illuminating over a solid angle of 4.pi. steradians, do not allow a precise simulation of the beam of photons. It is precisely an object of the present invention to provide a device for storing a source of photons and for irradiating a body by the radiation from said source, which overcomes the drawbacks of the devices of the prior art. One object of the present invention is an irradiation device adapted to deliver a beam of photons of precise dimensions, which is easily adjustable, with a device ensuring a first collimation. Another object of this invention is to provide a device enabling the radioactive sources to be changed without necessitating delicate manipulations on the site where the apparatus is used. The irradiation device according to the present invention remedies these drawbacks, in that it serves both as storage device and as irradiation device. The radioactive source is placed in position inside the support disc; it is adjusted at the moment of manufacture. The device provided with its already-adjusted source is then transported onto the site of use. It then suffices to removably mount it, for example by means of screws, on a support arm, for it to be ready to operate without any additional adjustment. When, after a determined time, the activity of the radioactive source has decreased and it has become necessary to replace it, the irradiation device is dismantled from its support arm, and an identical irradiation device comprising a new source is mounted in its place. Specialised man-power for changing the source is thus unnecessary. More precisely, the device for storing a source of photons and for irradiating a body by the radiation from said source is characterised in that it comprises: a body for biological protection provided with a cylindrical cavity of circular section and two so-called first and second passages respectively, these passages opening at one and the other of their ends in said cavity and on the outer wall of the body, PA0 a disc for biological protection, whose shape is complementary of that of the cavity of the body and presenting, on the one hand, a housing centred on an axis perpendicular to the axis of the cavity, this housing opening out on the side wall of the disc, PA0 a source of .gamma. radiation contained in said housing, PA0 a precollimator disposed at right angles to said first passage, PA0 means for rotating said disc between a first position for which said source is opposite the precollimator and a second position for which the source is in stored position. This device has the following advantages: due to its compactness, it may easily be mounted on its support in operational position, and due to the presence of a self-sufficient integrated biological protection, may be used directly for transporting radioactive sources, this biological protection being partly constituted by depleted uranium. This function of storage of the source makes it possible to avoid all operations of charging or discharging of the source on the site of use; it is of small dimensions, whilst ensuring a good biological protection and opposing direct or diffused leaks of radiation, due to the use of a rotating disc for positioning the source of photons; it is removable, and may easily be dismantled from its support arm; finally, the use of depleted uranium, whose capacity of absorption of the radiation is greater than that of lead, for producing the biological protection, makes it possible to reduce the weight of this device. In particular, this reduces the unbalance thereof when it is mounted on a support arm animated by a movement of rotation. For certain applications, it is necessary to deliver a light beam of precise dimensions, which is easily adjustable, serving to locate the beam of irradiation. For such applications, the biological protection disc of the storage device according to the invention further presents a passage disposed in the plane of the disc containing the axis of said housing, this passage opening at one and the other of its ends in two zones of the side wall of the disc capable of being simultaneously opposite said first and second passages; at least one optical fibre disposed in said passage in the disc, the ends of said fibre, respectively called receiver and emitter ends, being held at right angles to each of the ends of said passage via dismountable fixing means; an optical device fast with said body to produce a ray of light on the receiver end of said fibre, this device being disposed at right angles to said second passage. This preferred arrangement allows a perfect simulation of the beam of photons due to the use of the emitter end of the optical fibre which may be defined and positioned with precision; it also allows the easy replacement of the optical device adapted to produce the ray of light on the receiver end of the optical fibre. The irradiation device according to the invention also makes it possible, when the source is in stored position, to have access to each of the ends of the optical fibre via the passage of the body to which the optical device is disposed at right angles, whilst limiting the fixed positions of the biological protection disc to two. Thus, after the optical device has been dismantled, it is easy to introduce or remove the optical fibre in the short passage of the disc, and to adjust its positioning at right angles to the ends of said passage. According to a preferred arrangement of the invention, the axes of the receiver and emitter ends of the fibre define an angle close to 90.degree.. This arrangement enables the irradiation of the optical fibre in the course of functioning of the apparatus to be minimum. According to another preferred embodiment of the invention, the angle of rotation of the protection disc, when the source passes from the storage position to the position of irradiation, is 110.degree.. This arrangement limits the rate of leakage of the radiation from the source, when this latter is in storage position. It also enables the height of the protection body surrounding the disc to be limited. According to the invention, the device for storing a source of photons and for irradiating a body by the radiation from said source, preferably comprises on the one hand electric means for locking the disc in said first position allowing irradiation, and on the other hand mechanical means for automatically placing the disc in said second position corresponding to the storage of the source. Furthermore, the body is preferably constituted by a mass in which is included a block of depleted uranium, this block defining the portion of the wall of the cavity located around said source when said disc is in the storage position. An important advantage of the invention is that it allows a rapid replacement of the radioactive source. To this end, the invention also relates to a process for the replacement and transport of a radioactive source. This process is characterised in that it comprises the following successive steps of: transporting to its site of use an irradiation device provided with a new, previously adjusted source ready for use, the irradiation device acting as a radioprotection cask, dismantling the irradiation device carrying the worn-out source from the support arm on which it is fixed, mounting the irradiation device comprising the new, preadjusted radioactive source. Thus, the delicate adjustment of the source is effected when the device is manufactured. The irradiation device comprising the worn-out source is easily dismantled then the new irradiation device is easily mounted, without necessitating any additional adjustment and consequently without having to call upon specialised man-power.