SU‐FF‐T‐396: A Novel Approach for Determining Radiation‐Induced Second Cancer Risks From Selected Prostate Treatments Using Monte Carlo Simulations and An Anatomically‐Realistic Computational Phantom

Abstract

Purpose: There is an important and growing concern about the potential elevated risk of radiation‐induced second cancers associated new forms of radiation treatments. Concurrently with the recently formed AAPM Task Group 158 we have developed a framework to calculate volume‐averaged organ doses to patients using the Monte Carlo method. Using previously calculated organ doses from selected 3D‐CRT and IMRT treatments of prostate cancer, this study calculates radiation‐induced second cancer risks from these treatments utilizing the BIER VII report methodology. Method and Materials: A detailed model of a Varian Clinac 2100C was combined with the RPI Adult male computational phantom to calculate volume‐averaged organ doses from a 3D‐CRT 4‐field box treatment, a box treatment plus a 6‐field boost treatment, as well as a 7‐field IMRT treatment. Based on these organ doses, organ‐specific excess relative risks (ERR) and lifetime attributable risks (LAR) were determined using the methodology outlined in the recently published BEIR VII report. The total whole‐body LAR was determined for each treatment using arbitrary but clinically relevant monitor unit (MU) values of 10,000 and 40,000 for the 3D‐CRT and IMRT treatments. Results: For organs closest to the primary beam the ERR/MU is higher for the IMRT treatment compared to the 3D‐CRT treatments, resulting from an increase in the number of fields needed for IMRT treatments. For organs further away from the treatment volume the ERR/MU appears slightly higher for the 3D‐CRT treatments, as a consequence of the added neutron component of the 18‐MV primary beam. The total whole‐body LAR for the IMRT treatment was 2%, compared to about 0.4% from the box treatment and 0.9% from the box plus boost treatment. Conclusion: The tools presented in this study improve upon previous methodologies by using the most accurate dosimetry methods as well as the most practical second cancer risk models.