ESTRO 2023 - Abstract Book

S178

Saturday 13 May

ESTRO 2023

PD-0243 Proof-of-concept: Novel CBCT-based adaptive robust optimization in sinonasal cancer proton therapy N. Vatterodt 1,2 , R. Argota-Perez 3 , M.B. Sharma 4 , A.I.S. Holm 4 , U.V. Elstrøm 1 , K. Jensen 1 , S.S. Korreman 1,2,4 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark; 3 Herlev and Gentofte Hospital, Department of Oncology, Herlev, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective Anatomical variations in proton therapy for sinonasal cancer patients can potentially deteriorate treatment quality. Previous studies including robustness towards mucus variations has shown promising results, however using simple PTV- based optimization with artificially created nasal cavity filling scenarios. In this study, we investigated novel strategies combining adaptation and multi-image robust optimization by using actual anatomical variations from daily CBCTs. Materials and Methods A retrospective study on five sinonasal cancer patients was performed in RayStation 9A. For each patient, synthetic CTs (synCTs) were derived from daily CBCTs in MIM Maestro. In addition, two CTs with filled and cleared cavities were created by overwriting the CT numbers in the planning scans (using CERR software). Plans for four IMPT robustness schemes were generated as illustrated in Fig 1a: 1. Conventional robust optimized plans (cRO) 2. Initial full anatomical robust optimized plans including the two artificial scenarios (fRO) 3. Adaptation after the first week with individualized fRO plans using the first five fractions’ synCTs (afRO) 4. Weekly adaptation with individualized fRO plans including the previous five fractions’ synCTs (wafRO) For all plans, robust optimization and evaluation for geometrical uncertainties were performed assuming ±2mm setup and ±3.5% range uncertainty. All plans were approved according to passing criteria in Fig. 1b. Results were evaluated by comparison of target coverage (V95) and maximum dose to OAR (D0.03cc) for fraction doses recalculated on the daily synCTs and accumulated dose by deformable mapping of fraction doses to the planning CT. Results All approaches showed sufficient robustness in accumulated target coverage (Fig. 2a). Adaptive approaches using daily images showed comparable or better robustness than conventional plans and recovered two cases of underdosage for single fractions in the conventional plans. Largest improvements in accumulated and daily target coverage were obtained for weekly adaptation. The cost in maximum OAR dose in comparison to the gain in target coverage was highly dependent on structure and patient. This is demonstrated in Fig. 2b for structures that violated clinical constraints in total or daily doses for the adaptive approaches. Optimization using artificial scenarios compared unfavorably with any other plans. Conclusion