Dose-Driven Rule-Based Beam Configuration for Left-Sided Breast Fixed-Field IMRT: A Commercial TPS-Based Evaluation

Beam angle selection plays an important role in shaping dose distribution in fixed-field radiotherapy, yet additional beam placement in multi-beam settings is often empirically determined. This study proposes AutoBeams, a transparent dose-driven rule-based framework for generating six-beam configurations in left-sided breast fixed-field IMRT, and evaluates whether these configurations can produce clinically acceptable plans under a standardized commercial treatment planning system (TPS) optimization protocol. A retrospective cohort of 41 patients with left-sided breast cancer treated with six-beam coplanar fixed-field IMRT was included. For each patient, a clinical-angle reference (CR) was defined from the original clinical beam angles, and an AutoBeams configuration (AP) was generated using the same patient geometry and isocenter. CR and AP plans were generated and evaluated in Pinnacle under identical planning conditions, with beam-angle configuration being the only intended difference. AutoBeams sequentially selected beam angles from a predefined coplanar candidate set using dose-based scoring rules with angular separation constraints. AutoBeams generated beam configurations that differed from the clinical beam arrangements through limited angular adjustments. Under commercial TPS optimization, target dose metrics remained broadly comparable between AP and CR. AP showed lower heart dose metrics and spinal cord maximum dose, while contralateral lung low-dose exposure and contralateral breast mean dose increased, indicating OAR-specific trade-offs. In addition, AP plans demonstrated significantly lower total monitor units compared with CR (p < 0.001). Criterion-level evaluation showed that AutoBeams-generated configurations could generally be optimized into clinically acceptable plans. These findings support AutoBeams as a transparent and reproducible approach to beam-angle generation in left-sided breast fixed-field IMRT. .