The construction of compensators for MV photon beams

The use of compensators in order to achieve desired dose distribution had a long history and is well-established technique in radiation therapy planning. There are several different methods of calculation for compensator’ s shape discussed in literature. An alternative method is presented. The method is based on Cunningham's modification of Clarkson's method to calculate scattered radiation in beams with inhomogeneous cross-sectional dose distribution. The algorithm is rather general and could be applied to different required dose distributions in various clinical situations, different photon beams, and various compensating materials. The algorithm is feasible, quickly computable and versatile. The method is verified using film dosimetry in several practical situations manufacturing compensators out of steel granules and low melting alloy. Additional measurements were made using electronic portal imaging developed in our hospital. The results are compared with effective attenuation method.