Purpose: To quantitatively investigate the treatment delivery efficiency improvement using Spot-Scanning Proton Arc (SPArc) in comparison with automated step and shoot multi-field IMPT (IMPTauto) treatment and clinical IMPT treatment.
Methods: Total 12 cases from the three disease sites such as head neck, lung and brain cancer were retrospectively selected. SPArc and IMPTauto plans were generated with the same plan objectives and robustness parameters like clinical IMPT. SPArc utilized a partial arc with 2.5 degree of sampling frequency and IMPTauto used beam angles 40 degree apart covering the partial arc trajectory. A dynamic arc controller is designed to connect the velocity between control points during SPArc and IMPTauto treatment delivery with the following machine configurations (maximal gantry rotation speed 5 degree/s; The maximal acceleration and deceleration are 0.6 degree/s^2 and 0.48 degree/s^2; ±1 degree delivery tolerance window). Total treatment delivery time of each case was compared among SPArc, IMPTauto simulation and clinical treatment log files. 3D gamma index was used to evaluate the treatment delivery accuracy between SPArc and IMPTauto from the simulated dose reconstruction.
Results: The SPArc and IMPTauto delivery accuracy is clinical acceptable with ±1 degree delivery tolerance window. The average 3D gamma index comparison showed 97.85± 2.77% passing rate for SPArc and 99.07+ 0.73% for IMPTauto. Excluding the time spent on the initial patient setup and IGRT workflow, the SPArc could reduce the average treatment time to 175±74 s compared to the clinical IMPT (641±428s) and IMPTauto (595±254s). In comparison with clinical IMPT, SPArc simplified the clinical treatment workflow by eliminating the time for each beam request, preparation, transfer time from OIS to delivery system and manually gantry rotation between each treatment field. In comparison with IMPTauto, SPArc effectively reduced the energy layers and spot number.
Conclusion: SPArc technique could significantly simplify and improve the proton treatment workflow.
Funding Support, Disclosures, and Conflict of Interest: The senior author Xuanfeng Ding reports personal fee from the IBA speaker Bureau.