ON 3-DIMENSIONAL DOSE CALCULATION OF PHOTON-BEAM WITH WEDGE FILTERS

A wedge filter is one of the most commonly used beam modifying devices . The introduction of a wedge filter alters both the distribution of t he primary photon fluence and the first and second scatter patterns. T he effect of the wedge filter is normally expressed in terms of an exp onential attenuation function that is used to modify the primary photo n fluence. This paper describes a new three-dimensional (3-D) wedged f ield dose calculation algorithm. This algorithm automatically takes in to account (1) the scatter distribution pattern correction due to the effect of wedge filters and (2) the fixed primary photon fluence corre ction, by utilizing a tissue maximum ratio table calculated from the m easured percent depth dose of the wedge, a measured in-plane scan and a measured cross-plane scan of the largest rectangular wedge field siz e. As a result, the calculation accuracy achieved by this algorithm is better than the calculation accuracy achieved by other algorithms. Th e results show better than 1% accuracy of the wedge central axis perce nt depth dose calculation and better than 3% accuracy of the off-axis dose calculation when compared with measurements.