Author: Drexell Hunter Boggs, Carlos E. Cardenas, Jingwei Duan, Joseph Harms, Joel A. Pogue, Richard A. Popple, Courtney Bosse Stanley, Dennis N. Stanley, Sean Xavier Sullivan, Natalie N. Viscariello 👨🔬
Affiliation: Washington University in St. Louis, The University of Alabama at Birmingham, University of Alabama at Birmingham 🌍
Purpose: CBCT-guided online adaptive radiation therapy (OART) with Ethos for stereotactic accelerated partial breast irradiation (APBI) can mitigate inter-fraction variation, leading to dosimetric advantages over conventional RT. However, there are concerns regarding increased intra-fraction variation and patient discomfort caused by the prolonged treatment time (~30min), largely due to the reliance on a complex optimization scheme to produce high-quality, robust treatment plans. Here we investigate the feasibility of achieving similar dosimetry while reducing optimization time via “high-fidelity mode” (HF), a vendor-provided stereotactic planning module, through an in-silico analysis of the entire APBI OART session.
Methods: This IRB-approved study included 10 training patient datasets for tuning a HF planning template and 15 datasets for validation. For each validation patient, five OART treatment fractions were simulated using both templates (Non-HF/HF) via a virtual Ethos treatment planning and delivery system, resulting in the analysis of 300 validation plans (15*5*HF/Non-HF*adaptive/non-adaptive). Dose-volume-histogram (DVH) metrics, optimization times, and patient-specific-quality-assurance (PSQA) results were compared between HF and Non-HF via the Wilcoxon paired test.
Results: HF adaptive planning resulted in improved per-fraction breast V100%/50% (0.5%/3.3%), body V50% (27cc), and Paddick gradient index (0.17), but marginally inferior PTV V100% (0.2%) and lung V30% (0.6%) compared to Non-HF (p<0.005). There were no statistically significant differences in PSQA delivery accuracy (p ≥ 0.37) for any gamma criteria, with HF/Non-HF plans achieving 97.4%/97.5% passing rates at 3%/3mm. Notably, HF planning reduced the median [min,max] online optimization time by 5.4 [3.3,10.1]min per fraction (HF: 4.6 [3.2,7.1]min; Non-HF: 10.0 [6.8,16.4]min), significantly improving treatment efficiency and potentially reducing intra-fraction motion.
Conclusion: This work demonstrates that utilizing Ethos HF mode may significantly improve OART treatment efficacy for stereotactic treatments. Specifically for VMAT APBI, a 20% reduction in total treatment time was observed while maintaining plan quality, potentially leading to reduced patient discomfort and minimized intra-fraction motion.