A concave tray with divergent block for desired dose distribution around shielded region in megavoltage radiation therapy.

In clinical situations large numbers of rectangular divergent blocks are required at different off-axis positions from central axis to shield sensitive organs. Superiority of divergent blocks over non-divergent blocks on a flat tray lies in improving the dose homogeneity. A method has been developed to minimize the number of divergent shielding blocks by using a concave tray at the collimator. The results of use of a single divergent block are similar to that of the use of several divergent blocks, each to match at different off-axis positions in the radiation beam. This type of single concave tray thus provides a considerable ease of handling divergent blocks in a busy radiotherapy centre.