Patent Number: 047605901
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a multioperation accelerator of simple design, usable more particularly in radiotherapy for treatments using low or average amounts of energy. 2. Description of the Prior art In radiotherapy a distinction is made, among others, of two types of equipment, the radiation generators using radioactive sources, such for example as cobalt, and the particle (particularly electron) accelerators. These latter offer a great flexibility of use and allow high energies to be reached up to 40 MeV electrons and 25 MeV photons. However, such apparatus are costly. Particularly, the systems for adjusting and varying the power of the beam (so as to obtain the different operating conditions) acting on the acceleration parameters, particularly the HF power, have a great influence on the cost price of the installation. Furthermore, the cobalt generator has its own particular qualities which means that it is very greatly appreciated by doctors although handling of the radioactive sources requires precautions. The radiation of the cobalt is a photon radiation which is very penetrating despite a low energy (1.3 MeV photons) since 50% of the maximum dose is still available at a depth of 12 cm in the tissue. On the other hand, the "skin dose" is relatively high which means, in certain cases, surface irradiation which is too high with consequent risks of burning. Now, at the present time, it is possible to construct accelerator structures capable of supplying the electron energy (about 4 MeV) required for obtaining 1.3 MeV photons as with cobalt, and this for a relatively low cost price. SUMMARY OF THE INVENTION One of the aims of the invention consists then in perfecting a radiotherapy unit using a photon beam produced from an accelerator but whose characteristics are fairly close to those of cobalt with however additional facilities and particularly that of being able to use several types of beam. For example, a beam may be required having the same characteristics as cobalt radiation and also other beams having closely related characteristics, in particular improved characteristics in so far as the problem of the "skin dose" is concerned. Another aim of the invention is to provide a system of low cost price, of the same order of size as a cobalt generator. According to the general principle of the invention, the power of the accelerator remains constant (thus saving on the systems for adjusting the high frequency wave) whereas variations in operating conditions and characteristics of the beam are obtained by switching targets and/or filters at the output of the accelerator. More precisely, the invention provides a multioperation accelerator of the particle beam type comprising a target bombarded by said particle beam so as to generate a photon beam, wherein the HF power for supplying said accelerator is fixed at a predetermined level and it comprises several switchable targets and/or filters at the output of said accelerator, allowing a predetermined number of target-filter combinations to which correspond as many photon beams with different chosen characteristics.