S1754
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Results: The DVH, dose ratios, LET ratios, and number of energy layers for varying lateral spot size and beam energy spread are shown in Figures 1 and 2, respectively. As expected, reducing the lateral spot size yielded greater OAR sparing while maintaining comparable target coverage. A similar trend of improved OAR sparing was observed with reduced beam energy spread; however, the effect was less pronounced, likely due to changes in energy spread predominantly influencing the lower-dose tail rather than the Bragg peak, where the maximum dose is delivered. Overall, results indicated the potential of enhanced sparing with the DWA.
doi:10.1103/PhysRevAccelBeams.28.010401. [4] Takayama K, Briggs RJ. Induction Accelerators, Springer Berlin Heidelberg. 2011;23-37. [5] Heighway E, Hutcheon R. Nucl Instrum Methods Phys Res. Aug 1981;187(1):89-95.[6] Perl J et al. Med Phys. 2012; 39(11):6818-37.[7] IBA Beam Data Library. 2019. Github repository, https://gitlab.com/openmcsquare/MCsquare/- /tree/master/BDL. Keywords: proton, spot size, dielectric wall accelerator Digital Poster 3391 Treatment Plan Parameters Optimization in Prostate MRI-Guided Radiotherapy Parvin Mohammadyari 1 , Matteo Galetto 2 , Matteo Nardini 2 , Luca Boldrini 3,2 , Giuditta Chiloiro 2 , Giulia Panza 2 , Angela Romano 2 , Claudio Votta 2 , Marco De Spirito 4,2 , Lorenzo Placidi 2 1 Facoltà di Medicina e Chirurgia, Università Cattolica del Sacro Cuore, Rome, Italy. 2 Diagnostic Imaging and Oncological Radiotherapy Department, Fondazione Policlinico Universitario A. Gemelli, IRCCS, Rome, Italy. 3 Dipartimento di Scienze radiologiche ed ematologiche, Università Cattolica del Sacro Cuore, Rome, Italy. 4 dipartimento di neuroscienze, Università Cattolica del Sacro Cuore, Rome, Italy Purpose/Objective: This study aimed to evaluate the influence of key planning parameters and target geometry complexity on treatment efficiency and dosimetric performance in prostate online adaptive MRI-guided radiotherapy (MRIgRT) using the ViewRay MRIdian system. The objective was to identify parameter combinations that minimize treatment time while maintaining plan quality and robustness, providing a deeper understanding of the system’s optimization behavior to support a more efficient clinical workflow. Material/Methods: A total of 24 prostate SBRT plans were generated for each of 13 patients, resulting in 312 treatment plans overall. The plans were created using varying combinations of four primary planning optimization strategies implemented in the ViewRay MRIdian TPS: Segment Number, IMRT Efficiency, Fix Level and Accuracy Goal. Three distinct PTV geometries were recognized, representing increasing levels of modulation and anatomical complexity (see Figure 1). A total of 31 dosimetric and temporal metrics - including beam-on time, gamma index, Organ of Interest dose guidance and monitor units (MU) per fraction- were automatically extracted from plan reports and consolidated for statistical and correlation analysis. Feature importance was further explored using Principal Component Analysis (PCA) and three
Conclusion: Decreasing lateral spot size and beam energy spread resulted in greater OAR sparing while maintaining target coverage in a pediatric CNS case. Additional analyses across a broader CNS cohort are underway. For realistic optimization of the DWA system, the beam parameters identified as most favourable were a lateral spot size of approximately 1 mm and an energy spread of ~0.05% for 20 to 230 MeV. References: [1] Bancheri J et al. Nucl Instrum Methods Phys Res A. Dec 2024. 1069.[2] Maher MJ et al. Med. Phys. April 2025. doi:10.1002/mp.17868. [3] Lund CM et al. Phys. Rev. Accel. Beams. Jan 2025.
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