S1711
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Digital Poster 1035
Development of a Monte Carlo simulation model for a novel small-animal proton therapy beamline and validation over 3 years of preclinical experiments Ze Huang 1 , Jonathan Bortfeldt 1 , Franz S. Englbrecht 1 , Beatrice Foglia 1 , Johannes Gebhard 1 , Margarita Kozak 1 , Neeraj Kurichiyanil 1 , Thomas Rösch 1 , Katrin Schnürle 1 , Caroline Steinbrecht 1 , Matthias Würl 1 , Niels Bassler 2 , Per R. Poulsen 2 , Fardous Reaz 2 , Mateusz K. Sitarz 2 , Christian S. Søndergaard 2 , David Meer 3 , Sairos Safai 3 , Michele Togno 3 , Katia Parodi 1 , Marco Pinto 1 1 Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Garching b. München), Germany. 2 Danish Center for Particle Therapy (DCPT), Aarhus University Hospital, Aarhus, Denmark. 3 Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland Purpose/Objective: In the project “Small animal proton irradiator for research in molecular image-guided radiation- oncology” (SIRMIO), a portable beamline system was developed to degrade a low-energy clinical proton beam to 20-50 MeV and focus it to a 1 mm sigma size in air for small-animal irradiation [1]. Following characterization of the quadrupole magnets and materials of different beamline components, a Monte Carlo (MC) simulation model was constructed using the Geant4-based code G4beamline [2], fine-tuned to reproduce experimental results, and subsequently validated through multiple campaigns at clinical proton therapy facilities. Material/Methods: The properties of the permanent magnet quadrupoles and the energy degrader were experimentally characterized, and the beam optics was subsequently re-optimized from the initial design [1][3]. In several research campaigns, beam envelopes, both unscanned and scanned, were measured using EBT3 films and an in-house-developed MicroMegas (MM) detector with optical readout [4]. Beam range measurements were performed in a water tank and with a multi-layer ionization chamber (Giraffe, IBA, Louvain-la-Neuve, Belgium) combined with a 8-step degrader wheel. Transmission efficiency was evaluated using an in-house-built ionization chamber (SIRMIO IC) integrated into the beamline [5]. The MM and Giraffe detectors were validated against EBT3-film and water-tank measurements, respectively, while the SIRMIO IC was calibrated against PTW commercial ionization chambers (model 34045 and 7862, Freiburg, Germany). The MC model was validated against experimental data for beam range, shape, and transmission efficiency. Phase-space data from the validated simulation model were imported into a
Conclusion: Implementing a structured interruption management system, aligned with RCR and SEFM recommendations, significantly reduced clinically relevant delays without increasing workload. This organized approach formalized a practice already partly in place (Saturday treatments) and introduced multidisciplinary decision- making and ethical oversight. Although working on Saturdays—recommended by SEFM—is often difficult to obtain institutional approval for, the clinical and organizational benefits justify the effort. This initiative improved quality of care and workflow efficiency and encourages other departments to adopt similar systems, especially during bank holiday periods when interruptions tend to rise. References: 1) The Royal College of Radiologists. The timely delivery of radical radiotherapy: 4th ed. RCR, 2019.2) Sociedad Española de Física Médica (SEFM). Guía para la gestión de las interrupciones en radioterapia externa (in press), presented at SEFM Annual Congress 2024.3) De la Vega et al. Management of interruptions to fractionated radiotherapy treatments: Four and a half years of experience. Physica Medica 32 (2016)1551-15584) Gonzalez Ferreira et al. Effect of radiotherapy delay in overall treatment time on local control and survival in head and neck cancer: Review of the literature. Reports of practical oncology and Radiotherapy 20(2015)328-339 Keywords: treatment, interruptions, radiotherapy
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