Determination of composite field correction factor kpcsr,msr for Tomotherapy

Abstract

Abstract The purpose of this study is to determine the correction factor of the composite field (kpcsr,msr ) of Tomotherapy for head and neck cases and to investigate the influence parameters of the pcsr field. This study employed Exradin A1SL and A 16 as the investigated chambers, and EBT3 as the reference dosimeter. The pcsr fields were created based on cylindrical water solid phantom. The results of this study show that the kpcsr,msr values for both detectors increased with increasing field width (jaw), decreasing complexity level, and increasing pitch value. The yielded results indicate several factors affecting the kpcsr,msr values: target homogeneity, volume averaging effect, thread effect, and the difference of general recombination at the different field width. These results represent that kpcsr,msr is specific and depends on the parameters of the composite field. The kpcsr,msr values for head and neck cases vary from 0.978-1.028. This variation implies that the determination of pcsr field should be according to the parameters used in clinical conditions. Due to the different position of the chamber and the film, the target should have excellent dose homogeneity to avoid the different response of the detectors.