Patent Number: 039506517
Section: summary

The present invention relates generally to equipment for defining the field, or target area, to be radiated in the medical treatment of patients and, more particularly, patients suffering from cancer, malign tumours, or similar diseases. As is well-known, when a patient is to be treated by radiation for the purposes above mentioned, the first step to be carried out by the medical experts is to define the desired target area. This is usually made by X-raying. The target areas vary from different patients not only in terms of location on the patient but also as far as their sizes and shapes are concerned. By way of example, in the treatment of lung cancer, it is not unusual to have a target area covering say one lung. Accordingly, such target areas often have very irregular contours. This circumstance coupled with the fact that it is necessary on the one hand to make sure that the radiation reaches all of the target area and, on the other, does not hurt adjacent tissues not affected by the disease, involves that the target area must be determined and defined with great accuracy. A third factual circumstance to be noticed in this context is that patients suffering from cancer have to be treated on repeated occasions, typically once a week for several months. The radiation is emitted by a radiation source mounted inside a therapeutic unit and it emerges therefrom through an aperture in a shutter carried by that unit. That aperture is generally of circular or rectangular cross-section and it is consequently necessary downstream thereof to modify the effective cross-section of the radiated beam so that it matches the contour of the target area. This is in prior art arrangements made by the use of blocks consisting of a radiation-absorbing material, generally lead. From what has been said above it is apparent that each time a certain patient is to be radiation-treated a number of such blocks have to be arranged so that the target area is properly defined. It is common practice to mark that area on the body of the patient and during the arrangement of the absorption blocks to have the apparatus emit ordinary light through said aperture so that the proper configuration of the blocks can be checked. A major disadvantage of the method above accounted for is that the block arrangement work has to be repeated on each treatment occasion. A second disadvantage is that the patient has to be present during the corresponding time period. This does not only mean that the patient has to be in the treatment room for a considerably longer period of time than that during which he is treated but also correspondingly reduces the availability of the most expensive equipment for the treatment of further patients. The main object of the present invention is to eliminate the disadvantages and shortcomings above referred to. A method for defining the target area to be radiated in the treatment of such a patient is, according to the present invention, characterised by the steps of mixing a heavy metal fine grain powder with a pressure-sensitive, non-curing adhesive so that a plastically deformable composition is formed, compressing a disc-shaped member consisting of said composition for the purpose of increasing its density and geometrical stability, providing said member with a through aperture the contour of which is congruent with that of said target area, and mounting said member between the shutter and the target area in such a position that the contour of said second aperture is located inside the cross-section of the beam. The invention does also concern a composition for use in the carrying out of the above defined method and a therapy unit constructed so as to operate according to the method.