S1753
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Conclusion: This study demonstrates that robust single-beam pMBRT planning in RayStation is feasible but can be limited by a trade-off between PVDR and robust target coverage, and heavily dependent on beam depth and geometry. These findings provide insights into the effects of beam geometry and collimator parameters on PVDR and robustness, guiding future investigations on robust pMBRT planning. Keywords: pMBRT, robust optimization, PVDR Poster Discussion 3361 Effect of lateral spot size and beam energy spread on proton treatment plan Chau Giang Bui 1 , Jamiel Nasser 1 , Christopher M Lund 2 , Morgan J Maher 2 , Julien Bancheri 2 , Jason Yuan 1 , Amy Parent 3 , Monica Serban 4 , Jan Seuntjens 4,1 1 Medical Biophysics, University of Toronto, Toronto, Canada. 2 Medical Physics, McGill University, Montreal, Canada. 3 Radiation Therapy, University Health Network, Toronto, Canada. 4 Medical Physics, University Health Network, Toronto, Canada Purpose/Objective: The dielectric wall accelerator (DWA) was proposed as a low-cost, compact system for proton therapy1,2,3, with its design emerging from linear induction accelerators4. Given the degrees of freedom available in tailoring the beam parameters such as spot size, energy switching resolution, and delivery time, we seek to determine the range of achievable beam characteristics and their implications for treatment plan quality. In this work, we investigate how variations in lateral spot size and beam energy spread influence proton plan quality. Material/Methods: A linear beam optics model of the DWA3 was developed and validated using the TRANSOPTR5 code; the beam parameters exiting the DWA were manually adjusted to achieve the desired spot sizes and energy spreads at isocenter. These adjusted beam parameters were subsequently passed through components of a generic nozzle model in TOPAS6. Lateral spot size, defined in air at isocenter as one standard deviation of the beam profile, was varied across 1, 3, 5, 7, and 10 mm. Beam energy spread, expressed as the percentage ratio of energy variation to the nominal energy, was varied over 0.005%, 0.05%, 0.5%, 1%, 5%, and 15%. Treatment plans were generated for a pediatric central nervous system (CNS) case. Plan quality metrics including DVH, the ratio of dose inside to dose outside the CTV, and the ratio of LET inside to LET outside the CTV were evaluated. All results were benchmarked against reference data from the IBA beam data library7.
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