Purpose: To address the challenges of generating a deliverable and efficient spot-scanning proton arc(SPArc) plan for a proton therapy system. We developed a novel SPArc optimization algorithm(SPArcDMSP) by directly incorporating machine-specific parameters such as mechanical constraints and delivery sequence.
Methods: A SPArc delivery sequence model(DSMarc) was built based on the machine-specific parameters of the prototype arc delivery system, IBA ProteusONE®, including mechanical constraint(maximum gantry speed, acceleration, and deceleration speed) and delivery sequence(energy and spot delivery sequence and time). SPArcDMSP resamples and adjusts each control point's delivery speed based on the DSMarc calculation through the iterative approach(Figure1). In SPArcDMSP, clinical users could set the expected arc delivery time and gantry max acceleration as a mechanical constraint during the plan optimization. Four representative cases(brain, head neck, liver,and lung cancer patients) were selected to test SPArcDMSP. Two kinds of SPArc plans were generated using the same planning objective functions:(1)SPArcDMSP plan meeting the maximum allowable gantry acceleration speed(0.6deg/s2); (2)SPArcDMSP-user-speed plan with a user pre-defined delivery time and constraint the acceleration speed<0.1deg/s2. Additionally, the arc delivery sequence was simulated based on the DSMarc and was compared.
Results: With a similar objective value, number of energy layers and spots, both SPArcDMSP and SPArcDMSP-user-speed plans could be delivered continuously within the ±1 degree tolerance window. The SPArcDMSP-user-speed plan could minimize the gantry momentum change based on clinical users' input compared to the SPArcDMSP, which could help relieve mechanical challenges to accelerate or decelerate the hundreds of tons of gantry(Figure2&3).
Conclusion: For the first time, clinical users not only could generate a SPArc plan meeting the mechanical constraint of their proton system but also directly controlled the arc treatment speed and momentum changes of the gantry during the plan optimization. This work paved the roadmap for the clinical implementation of proton arc therapy in the treatment planning system.
Funding Support, Disclosures, and Conflict of Interest: The research project in part is supported by Ion Beam Application S.A. (Belgium). Xuanfeng Ding, Xiaoqiangn Li and Di Yan has a patent related to particle arc therapy and the patent has been licensed to IBA. Xuanfeng Ding reported personal fee from IBA speaker Bureau