Clinical implementation considerations for proton dose-driven continuous scanning: comparative analysis of breakpoint determination methods

Objective.We evaluated different breakpoint (BP) strategies and the impact of scan path optimization on dose accuracy, beam interruptions, and delivery efficiency in proton dose-driven continuous scanning (DDCS). Our goal is to provide insights for the effective clinical implementation of DDCS.Approach.Proton pencil beam scanning plans were retrospectively simulated for DDCS with beam current optimized for the shortest beam delivery time (BDT). Five BP strategies were evaluated: three spot distance (SD)-based (SD1, SD1.5, SD2) using SD thresholds, and two SR-based (SR1, SR0) using the ratio of MU delivered at the planned spot to that delivered in transit. Simulations included three scan paths (default, length-optimized, time-optimized). Comparative analysis included BP fraction (beam interruptions), dose accuracy, and BDT.Main results.SD-based approaches achieved excellent dosimetric accuracy, with 2%/2 mm Gamma pass rates >98% and CTV DVH RMSE <1% across all BP thresholds and scan paths. SD2 with length-optimized path minimized BPs (median 1.1%, range 0%-6.7%) while maintaining high dose accuracy, making it the preferred choice when minimizing dose deviations and BPs is the priority. SR-based approaches had shorter BDTs, maintaining >95% Gamma pass rates and <2% CTV DVH RMSE with optimized scan path. SR0 with time-optimized path is suitable when BDT is critical. Scan path optimization reduced BPs for SD-based methods and improved dose accuracy for SR-based methods. If only the default serpentine path is available, caution is required for lung treatments to ensure clinically acceptable dose with SR-based methods.Significance.Dose accuracy can be maintained without reducing the beam current optimized for BDT in DDCS. SD- and SR-based methods show complementary strengths: SD2 with a length-optimized path minimizes dose deviations and BPs, whereas SR0 with time-optimized path offers shorter BDT and maintaining acceptable dose deviations. These findings provide guidance for implementing proton DDCS to balance dose accuracy, beam interruptions, and delivery efficiency according to clinical needs.