ESTRO 2025 - Abstract Book

S2689

Physics - Dose calculation algorithms

ESTRO 2025

Conclusion: Higher energies and lower beam currents (<5 MU/s) demonstrated more robust delivery timing against T rise variations. Our findings suggest that a T rise measurement uncertainty below 10% is sufficient to maintain total beam delivery uncertainty under 3%. This implies an upper limit to our T rise measurement uncertainty in order to keep the modelling of the DDCS beam delivery system accurate. Further work will analyse multiple prostate plans with varying spot patterns and energy levels. Other ongoing investigations include characterization of other timing parameters like RF-kicker delays, with the goal of developing a validated beam delivery model for treatment time optimization.

Keywords: Proton therapy, DDCS, Beam Time Optimization

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Digital Poster Monte Carlo-based 3D secondary dose check: commissioning and using for small fields and complex plans Anna L Petoukhova, Guus B Spenkelink, Jean-Paul J.E. Kleijnen Department of Medical Physics, Haaglanden Medical Center, Leidschendam, Netherlands Purpose/Objective: Patient-specific quality assurance (QA) is very important in radiotherapy, especially for small fields and complex plans. Monte Carlo (MC)-based 3D secondary dose check software (SciMoCa) was commissioned and benchmarked against well-established TPS RayStation (RaySearch laboratories). Material/Methods: MC-based secondary dose check software was commissioned based on custom beam models of an Elekta VersaHD accelerator. Water phantom measurements (PDDs, profiles and output factors) were used for commissioning of RayStation and SciMoCa. RayStation Collapsed Cone (CC) plans of 34 patients (breast, head-and-neck, prostate, bladder, kidney, anus, cervix, stereotactic lung, glioma and multiple brain metastases) were recalculated in SciMoCa with MC dose-to-medium and dose-to-water (1% accuracy, grid size of the original plan). Coplanar and non-coplanar VMAT treatment plans with 6, 10 MV and 6 MV FFF energies were used. For all these plans, ArcCHECK measurements (1) were performed and compared with the results of SciMoCa. Additionally, dose calculations in Mobius3D were performed with the same gamma criteria and compared with SciMoCa results. Moreover, RayStation MC commissioning (2) and calculations were performed and compared with MC dose-to medium in SciMoCa. Gamma pass rate was calculated with 3% absolute global dose difference and 3 mm distance-to-agreement criteria with a threshold of 10%. Results: The mean pass rate for all ArcCHECK measurements in comparison to RayStation CC calculations was 98.2±1.5% with 3%/3 mm criteria. The mean pass rate of secondary dose calculation in SciMoCa for 34 patients was 99.2±1.7% for dose-to-medium and 99.0±1.2% for dose-to water (see figure 1). The mean pass rate of the secondary dose calculations in Mobius3D was 96.5±6.9% with the same criteria. The mean pass rate of secondary dose calculation in SciMoCa (in dose-to-medium) of CC and MC RayStation plans was 99.1±2.0% and 99.7±0.4%, respectively (see figure 2).