ESTRO 2025 - Abstract Book

S3374

Physics - Machine learning models and clinical applications

ESTRO 2025

1067

Digital Poster An Automated Patient-Specific Beam Angle Optimization Technique for Deep Learning Auto-Planning in Early Breast Cancer Treatment Michele Zeverino 1 , Gian Guyer 1 , Wendy Jeanneret-Sozzi 2 , Fernanda Herrera 2 , Raphael Moeckli 1 1 Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland. 2 Radiation Oncology Department, Lausanne University Hospital, Lausanne, Switzerland Purpose/Objective: To enhance a deep-learning (DL) auto-planning model for simultaneous integrated boost (SIB) in left-sided breast treatment by optimizing patient-specific arc spans and beam angles in VMAT and IMRT techniques to reduce normal tissue exposure. Material/Methods: The DL auto-planning system in RayStation TPS uses a mimicking algorithm to replicate dose distributions based on planner-selected techniques. We developed an automated approach to derive optimal beam angles from intensity profiles in terms of DoseArea (DA) product [MU·cm²] of two full VMAT arcs used in the mimicking process. For each patient, the DA was calculated for each arc segment (3° spacing), producing individualized DA profiles. Three DA thresholds (200, 400, and 800 MU·cm²) were used to reduce the number of segments: the angles with DA below these thresholds were eliminated to generate VMAT 200 , IMRT 400 , and IMRT 800 plans (see Figure 1 for details). Due to the minimum arc span limitations in the TPS (≥24°), IMRT was applied for DA ≥ 400 using a minimum spacing of 12° between beams. A second mimicking was conducted on these configurations producing the final plans, and results were retrospectively compared to clinical VMAT DL-based auto-plans that used two reversed continuous partial arcs (VMAT clin ) for 20 patients in terms of PTV coverage, OAR sparing, and total MU, with statistical significance at p<0.05 (Wilcoxon test).

Results: Optimal start/stop angles for VMAT 200 had median values of 290°/340° and 108°/170°, for internal and external partial arcs, respectively, compared to 300°/150° continuous partial arc for VMAT clin . Median beam numbers were 8 (IMRT 400 ) and 5 (IMRT 800 ), with angles varying with the PTV Boost position. IMRT 400 and IMRT 800 provided superior PTV coverage but with decreased conformity; IMRT 800 had increased hot-spot volumes (V105% = 1.9% vs 1.4%) in