Room: Stars at Night Ballroom 1
Purpose: Photon radiotherapy techniques typically devote considerable attention to limiting the exposure of healthy tissues outside of the target volume. Numerous studies have shown, however, that commercial Treatment Planning Systems (TPS's) significantly underestimate the absorbed dose outside of the treatment field. The purpose of this study was to test the feasibility of quickly and accurately calculating the total absorbed dose to the whole body from photon radiotherapy in individual patients.
Methods: We created an extended TPS, CERR-LSU, by implementing a physics-based analytical model for the absorbed dose from stray photons during photon therapy into a research TPS, CERR. We configured and validated CERR-LSU using measurements of 6- and 15-MV photon beams in water-box and anthropomorphic phantoms. We characterized the additional computation time required for therapeutic and stray dose calculations in a 44x30x180 cm3 water-box phantom.
Results: CERR-LSU achieved superior dosimetric accuracy than CERR in both water and anthropomorphic phantoms, especially outside of the primary treatment field. In the anthropomorphic phantom, CERR-LSU increased the generalized-gamma-index passing rate by a factor of 10 and decreased the median dosimetric discrepancy in the out-of-field region by a factor of 26. CERR-LSU achieved an average discrepancy less than 1% in and near the treatment field and less than 1 mGy/Gy far from the treatment field in the anthropomorphic phantom. Characterization of computation time revealed that on average, CERR-LSU only required 7% longer than CERR to calculate the total absorbed dose.
Conclusion: The results of this work suggest that it is feasible to quickly and accurately calculate whole-body doses inside and outside of the therapeutic treatment field in individual patients on a routine basis using physics-based analytical dose models. This additional capability enables a more personalized approach to minimizing the risk of radiogenic late effects, such as second cancer and cardiac toxicity, during radiotherapy treatment planning.
Funding Support, Disclosures, and Conflict of Interest: Louisiana State University Graduate School Economic Development Assistantship, DAAD (translates to German Academic Exchange Service) short-term research grant, Nuclear Regulatory Commission (NRC; award NRT-HQ-84-15-G-0017). Portions of this research were conducted with high performance computing resources provided by Louisiana State University (http://www.hpc.lsu.edu).