Po‐Thur Eve General‐10: Dose gradient analyses in the prostate organ motion: treatment plan evaluation independent of DVH
The aim of this study is to investigate internal organ motion using the profiles of the PTV dose gradients independent of DVH. In this study, the four‐beam box (4BB) and 5‐beam IMRT of three prostate patients were analyzed. Patients with small (17.3 cm3), medium (51.6 cm3) and large (87.1 cm3) prostate volumes were selected from Grand River Regional Cancer Center (GRRCC). A Pinnacle3 planning system was used to determine the PTV dose profiles crossing the isocenter in the L‐R, A‐P and S‐I directions. The convolution of the “static” dose and the Gaussian distribution were used to describe the discrepancy between the prescribed and delivered dose affected by patient repositioning and internal organ motion. The “shoulder” shape of the PTV profile determines the dose delivered to the tumor and critical organs when internal organ motion was considered. A “line equivalent uniform dose” (LEUD) was used to evaluate the shoulder dose deviation. The profile shapes influence the organ at risk (OAR) dose distribution more significantly for 4BB in comparison with IMRT especially in the posterior direction. The LEUD deviation in the range from 7.7% to 2.8% for S‐I and A‐P directions, respectively, was observed for the standard deviation of 1. The analysis of the PTV profile shape is a powerful tool for further improvement of IMRT treatment plan optimization. The results can be included as a parameter in the objective function used in the IMRT optimization.