ESTRO 2025 - Abstract Book

S3492

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

ESTRO 2025

Conclusion: Our findings indicate that the dose from high LET particles significantly contributes to post-treatment imaging changes.

Keywords: Proton treatment, LETd

References: 1. Souris K, Lee JA, Sterpin E. Fast multipurpose Monte Carlo simulation for proton therapy using multi- and many core CPU architectures. Med Phys. 2016;43(4):1700-12. 2. Meier R, Knecht U, Loosli T, Bauer S, Slotboom J, Wiest R, et al. Clinical Evaluation of a Fully-automatic Segmentation Method for Longitudinal Brain Tumor Volumetry. Scientific Reports. 2016;6.

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Digital Poster Comparison of spot size between conventional proton beams and dielectric wall accelerator proton beams Chau Giang Bui 1 , Chris M Lund 2 , Jamiel Nasser 1 , Morgan J Maher 2 , Julien Bancheri 2 , Jason Yuan 1 , Amy Parent 3 , Monica Serban 4,5 , Jan Seuntjens 1,5 1 Medical Biophysics, University of Toronto, Toronto, Canada. 2 Medical Physics, McGill University, Montreal, Canada. 3 Radiation Medicine, University Health Network, Toronto, Canada. 4 Radiation Oncology, University of Toronto, Toronto, Canada. 5 Medical Physics, Princess Margaret Cancer Centre, Toronto, Canada Purpose/Objective: Proton therapy (PT) has demonstrated greater precision and superior healthy tissue sparing compared to photon radiotherapy for various sites; however, protons are expensive and thus difficult to install in publicly-funded healthcare systems. The dielectric wall accelerator (DWA) was proposed as a low-cost, compact PT system 1 , with its design emerging from linear induction accelerators 2 . In this work, we present a pipeline for source-to-patient simulations of a DWA beamline and compare the spot sizes from this model system to those from conventional PT machines, as spot size influences PT treatment plan quality. Material/Methods: A linear beam optics model of the DWA 3 was developed and validated using the TRANSOPTR 4 code. The proton bunches were simulated through a DWA beamline, which included a pre-accelerator, collimated bend section, primary accelerator, and three focusing magnets in the treatment head 5 . Eight magnet settings (energy bins) were used to cover the energy range of 20 to 230 MeV. These bunches were subsequently passed through nozzle components using TOPAS 6 . For comparison, a proton beam line from IBA 7 was simulated in TOPAS, with and without Lexan and polyethylene range shifters of 7-g/cm 2 thickness. For all configurations, lateral spot sizes were measured in air; longitudinal spot sizes in water. Results: The lateral and longitudinal spot sizes are shown in Figures 1 and 2, respectively. The spot size trends for conventional PT (IBA) are in agreement with previous literature 8 . Compared to IBA proton beams, DWA protons exhibit a 67.0% average reduction in lateral spot size over ranges from 7 cm to 21 cm (corresponding to 100 to 175 MeV) and a 76.8% reduction in ranges below 7 cm, averaged over both range shifters. For the longitudinal spot size, DWA protons have a 21.5% average reduction compared to IBA due to their lower beam energy spread. Since achieving a spot size of 5 mm or less has been shown to yield highly conformal plans 9 , DWA protons have the potential to improve clinical plan quality.