Leveraging High-Fidelity Mode for Improved Online Adaptive Stereotactic Accelerated Partial Breast Treatment Efficiency

Purpose: Cone beam computed tomography guided online adaptive radiation therapy (OART) for stereotactic accelerated partial breast irradiation (APBI) can help mitigate the effects of interfraction lumpectomy bed variation. However, OART leads to a prolonged treatment time due to daily reoptimization of the treatment plan, potentially increasing patient discomfort and intrafraction variation. Here, we investigate the feasibility of using a stereotactic radiation therapy optimization feature, high-fidelity (HF) mode, through an in silico analysis of the entire APBI OART session. Methods and Materials: This retrospective in silico institutional review board–approved study included 25 patient data sets; 10 training patients allowed for iterative tuning of an HF planning strategy aiming to reduce optimization time with comparable plan quality to our previous non-HF planning strategy. Five OART treatment fractions were emulated for the remaining 15 patients in a virtual treatment planning and delivery system using both templates (with/without HF), resulting in the analysis of 330 validation cohort plans, including reference/nonadaptive/adaptive plans (initial plan/recalculated initial plan/reoptimized plan). Dose-volume-histogram metrics, optimization times, and patient-specific quality assurance results were compared with/without HF via the Wilcoxon paired test. Results: HF adaptive planning resulted in improved per-fraction breast V100%/50% (0.2%/3.3%), Ribs D0.01cc (0.2 Gy), and Paddick conformity/gradient indices (0.01/0.17), but led to marginally inferior planning target volume V100% (0.2%) and lung V30% (0.2%) compared to non-HF (P < .005). HF planning reduced the median online optimization time by 54% (5.4 minutes) per fraction, significantly improving treatment efficiency. There were no statistically significant differences in patient-specific quality assurance delivery accuracy, as indicated by the gamma passing rate (P ≥ .29), with both HF and non-HF plans achieving >97% at 3%/3 mm. Conclusions: This work demonstrates that leveraging Ethos v2.0 HF mode may significantly improve stereotactic OART treatment efficiency for volumetric modulated arc therapy APBI, with >50% reduction in optimization time observed while maintaining plan quality on a nonclinical system, potentially leading to reduced patient discomfort and mitigated intrafraction variations.