Effects of Phantom Factor on Shape Differences in Tomotherapy Water-equivalent Phantoms

Abstract

Purpose: The purpose of this study was to evaluate the effects of phantom factor on the verification of measured doses using cheese phantoms in tomotherapy. Methods: Two plans for dose verification (plan classes and plan class phantom sets with a virtual organ at the risk set) were evaluated. The calculated and measured doses were compared with and without the phantom factor using cheese phantoms. Additionally, the phantom factor was evaluated for two conditions (TomoHelical/TomoDirect) in clinical cases (breast and prostate). Results: When applying a phantom factor of 1.007, the deviation between the calculated and measured doses increased in Plan-Class and TomoDirect, decreased in TomoHelical, and increased in both clinical cases. Conclusion: When conducting dose verification, the effects of one phantom factor on measurement conditions may differ depending on when phantom factors were obtained (irradiation technique and irradiation field). It is therefore necessary to consider changes in measured doses due to changes in phantom scattering.