ESTRO 2025 - Abstract Book

S3567

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

Keywords: Chemical Dosimetry, Radical Yield Validation, MC

References: [1] Pastina, B., LaVerne, J.A., Hydrogen Peroxide Production in the Radiolysis of Water with Heavy Ions. J. Phys. Chem. A 1999, 103 , 1592–1597. [2] Hiroki, A., Pimblott, S.M., LaVerne, J.A., Hydrogen Peroxide Production in the Radiolysis of Water with High Radical Scavenger Concentrations. J. Phys. Chem. A 2002, 106 , 9352–9358.

4422

Digital Poster A comparative study of dynamic and static proton arc therapy

Helge Henjum 1 , Andreas H Handeland 2,1 , Erlend Hartvigsen 1 , Camilla H Stokkevåg 2,1 , Kristian S Ytre-Hauge 1 1 Department of Physics and Technology, University of Bergen, Bergen, Norway. 2 Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway Purpose/Objective: Proton Arc Therapy (PAT) is an emerging modality with potential to reduce dose to healthy tissue, compared to conventional intensity-modulated proton therapy (IMPT). PAT may be delivered using static arcs, comprising arcs of multiple fixed fields or dynamic arcs, where the beam is delivered continuously during gantry rotation. This study evaluates dynamic and static PAT compared to IMPT in terms of dosimetric properties, delivery efficiency, and optimization potential. Material/Methods: Treatment plans for IMPT, dynamic and static arc, were generated for a pediatric ependymoma patient using RayStation version 2023b. All plans were robustly optimized to a dose of 54 Gy(RBE) to the CTV, including a 3% calibration curve uncertainty and ±2 mm isocenter shifts. Plan metrics evaluated included RBE 1.1 -weighted dose, linear energy transfer (LET)-weighted dose (LWD), and LET distributions. Additional plans were created incorporating LET-optimization aiming to increase the LET in the CTV. Beam parameters were evaluated, and estimated delivery times were calculated assuming a 5°/s gantry rotation, 1 µA beam current, 1 s energy down-switching, and 0.5–5 s energy up-switching. Results: All modalities showed comparable CTV-coverage, while the dynamic arc plan had slightly lower OAR-doses, and IMPT provided the highest (Figures 1a, d). The median IMPT dose for the right cochlea was 18.4 Gy(RBE) compared to 13.0 and 14.1 Gy(RBE) for the dynamic and static arc plan, respectively, for the plans without LET-optimization. However, dynamic arc provided the highest LET (Figures 1b, e) in the OARs, leading to the highest LWD (Figures 1c, f). The max LWD (d2%) to the brainstem was 59.2 Gy(RBE) for dynamic arc, compared to 56.7, and 57.5 Gy(RBE) for static arc and IMPT, respectively, for the plans without LET-optimization. Both LET and LET-weighted dose were lowest in OARs for static arc (Figures 1b, c, e, f) while LET-optimization increased LET in the CTV slightly bringing it closer to dynamic arc without increasing dose or LET in OARs. Further, while dynamic arc utilized fewer energy layers than static arc, they exhibited higher spot weighting (Figures 2a, b). Delivery times were highest for static arc, varying from 18-73 minutes, and thus highly dependent on the energy up switching time (Figure 2c).