SU‐E‐T‐13: A Comparative Dosimetric Study On Radio‐Dynamic Therapy for Pelvic Cancer Treatment: Strategies for Bone Marrow Dose and Volume Reduction

Purpose: Radio‐dynamic therapy (RDT) is a potentially effective modality for local and systemic cancer treatment. Using RDT, the administration of a radio‐sensitizer enhances the biological effect of high‐energy photons. Although the sensitizer uptake ratio of tumor to normal tissue is normally high, one cannot simply neglect its effect on critical structures. In this study, we aim to explore planning strategies to improve bone marrow sparing without compromising the plan quality for RDT treatment of pelvic cancers. Methods: Ten cervical and ten prostate cancer patients who previously received radiotherapy at our institution were selected for this study. For each patient, nine plans were created using the Varian Eclipse treatmentplanning‐system (TPS) with 3D‐CRT, IMRT, and VMAT delivery techniques containing various gantry angle combinations and optimization parameters (dose constraints to the bone marrow). To evaluate the plans for bone marrow sparing, the dose‐volume parameters V5, V10, V15, V20, V30, and V40 for bone marrow were examined. Effective doseenhancement factors for the sensitizer were used to weigh the dose‐volume histograms for various tissues from individual fractions. Results: The planning strategies had different impacts on bone marrow sparing for the cervical and prostate cases. For the cervical cases, provided the bone marrow constraints were properly set during optimization, the dose to bone marrow sparing was found to be comparable between different IMRT and VMAT plans regardless of the gantry angle selection. For the prostate cases, however, careful selection of gantry angles could dramatically improve the bone marrow sparing, although the dose distribution in bone marrow was clinically acceptable for all prostate plans that we created. Conclusion: For intensity‐modulated RDT planning for cervical cancer, planners should set bone marrow constraints properly to avoid any adverse damage, while for prostate cancer one can carefully select gantry angles to improve bone marrow sparing when necessary.