S1909
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
beam models. All profiles exhibited 100% GPR with 2%/1 mm criteria. Output factors and beam quality indices agreed within 2% of measurement. Maximum statistical uncertainties at any point were shown to be 0.6% (photons) and 1.4% (electrons). Simulated relative doses within the cell irradiation setup agreed within 2% of measurement at all SSDs, confirming the models’ predictive accuracy for relative dose, dose rate, and DPP. Conclusion: TOPAS models of the Elekta Synergy and UHDR- enabled Precise linacs were comprehensively validated and shown to accurately reproduce measured dosimetry for standard and UHDR beams. Cell- irradiation geometries were modelled and shown to reliably predict and verify delivered dose. The complete model suite—including all electron applicators, jaw and MLC configurations, and phase- space files (6 MV photon, 10 MeV standard and eFLASH) — provides a robust framework for dose verification and prediction, supporting radiobiological research where standard dosimetry methods are unreliable or impractical. References: Perl, J. Shin, J. Schumann, B. Faddegon, and H. Paganetti. TOPAS: An innovative proton Monte Carlo platform for research and clinical applications. Medical Physics, 39:6818, 2012Anna Tesei, Anna Sarnelli, Chiara Arienti, Enrico Menghi, Laura Medri, Elisa Gabucci, Sara Pignatta, Mirella Falconi, Rosella Silvestrini, Wainer Zoli, et al. In vitro irradiation system for radiobiological experiments. Radiation Oncology, 8:1–12, 2013.Elizabeth Claridge Mackonis, Natalka Suchowerska, Pourandokht Naseri, and David R McKenzie. Optimisation of exposure conditions for in vitro radiobiology experiments. Australasian physical & engineering sciences in medicine, 35:151–157, 2012. Keywords: TOPAS Monte-Carlo, FLASH, dose validation Monte Carlo optimization restores PTV coverage without increasing OAR dose for conventional and stereotactic radiotherapy in lung cancer patients Jesus Rojo-Santiago 1 , Noelle CMG van der Voort van Zyp 2 , Dieke Bruijn-Krist 1 , Anna L. Petoukhova 1 1 Medical Physics, Haaglanden Medical Center, Leidschendam, Netherlands. 2 Radiation Oncology, Haaglanden Medical Center, Leidschendam, Netherlands Purpose/Objective: Accurate dose calculation in lung radiotherapy (RT) remains challenging due to tissue heterogeneity and electronic disequilibrium. Although Collapsed Cone (CC) algorithms are commercially available and widely Digital Poster Highlight 2967
patients and diminishes model-based predicted benefit of proton therapy. Physics and Imaging in
Radiation Oncology. 2025 Oct 1;36. Keywords: RapidArc Dynamic, SABR
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A TOPAS Monte-Carlo model of standard and FLASH-enabled Elekta linacs for in vitro dose verification and prediction. Oran McElligott 1,2 , Cathy Fleming 1,2 , Brendan McClean 1,2 1 Department of Physics, St. Luke's Radiation Oncology Network, Dublin, Ireland. 2 School of Physics, University College Dublin, Dublin, Ireland Purpose/Objective: This work aimed to construct and comprehensively validate in silico models of a standard Elekta Synergy linac and a locally modified, ultra-high dose-rate (UHDR)-enabled Elekta Precise linac using the TOol for PArticle Simulation (TOPAS) Monte Carlo (MC) toolkit. These models support dose verification and prediction for ongoing dosimetric and pre-clinical radiobiological studies, where standard dosimetry methods are unreliable or impractical. Material/Methods: Detailed MC models of both linacs were built in TOPAS for three beam models (6 MV photons, 10 MeV standard and 10MeV UHDR (“eFLASH”)). Source parameters and scattering foil geometries were iteratively optimized to match measured data. For standard photon and electron beams, simulated percentage depth dose (PDD) curves and beam profiles were validated with high-resolution PTW microDiamond measurements in water. For the eFLASH beam, radiochromic film and RP-FLASH scintillator measurements were used for PDD and profile validation. Additional verification metrics included field size factors, output factors, and beam quality specifiers (i.e. TPR and R ₅₀ ).Specialised phantoms, custom built to hold cell flasks for in vitro experiment, were also modelled in TOPAS. Simulated irradiations were compared to film measurements to verify dose to irradiated cells within these configurations. The validated models were further employed to predict relative dose-rate changes with varying dose-per-pulse (DPP). These predictions were confirmed experimentally using ion chamber, film and RP-FLASH measurements. Comprehensive uncertainty analyses were performed for all simulations and physical measurements. Results: MC-simulated PDDs showed excellent agreement with measurements beyond dmax, achieving 100% gamma- passing rates (GPRs) for 1%/1 mm criteria, for all three
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