Abstract
BACKGROUND: To address the issue where single Volumetric Modulated Arc Therapy (VMAT) delivery times often exceed a patient's comfortable breath-hold capacity of approximately 20s during Deep Inspiration Breath-Hold (DIBH) radiotherapy for breast cancer, this study proposes and systematically evaluates a novel time-control optimization strategy. The goal is to reduce overall delivery time and improve temporal uniformity across individual arcs within the United Imaging Healthcare (UIH) uTPS platform. METHODS: The study included 32 left-sided breast cancer patients, with 16 having undergone breast-conserving surgery and 16 having undergone mastectomy. For each patient, 16 distinct VMAT plans were generated to compare combinations of optimization algorithms (FMO/SPO), fluence modes (FF/FFF), and various dose rates. A novel bounding factor analysis was introduced to quantify delivery bottlenecks by assessing the relative contributions of gantry rotation, MLC movement, and MU delivery to the overall treatment time. RESULTS: The time-control strategy effectively reduced the mean arc delivery time and improved its uniformity across all tested combinations. The bounding factor analysis revealed that FMO plans were primarily limited by Multi-Leaf Collimator (MLC) movement, whereas SPO plans were predominantly limited by Monitor Unit (MU) delivery. Consequently, when the time-control strategy was applied to FMO plans, it shortened delivery times by restricting MLC mobility, which led to some dosimetric degradation. In contrast, for SPO plans, the strategy maintained or enhanced MLC movement while significantly reducing time, thus preserving or even improving dosimetric quality. Notably, the combination of SPO with the high-dose-rate (1400 MU/min) FFF mode reduced single-arc delivery times to approximately 10s. CONCLUSIONS: The proposed time-control strategy is a superior solution for shortening delivery time and enhancing patient comfort without significant dosimetric compromise.