Room: Stars at Night Ballroom 1
Purpose: Spot-scanning proton arc therapy (SPArc) is a brand new concept of proton therapy delivery technique which allows simultaneously delivering spot-scanning proton beam treatments while rotating the gantry to improve plan quality, robustness, and delivery efficiency. This study reported the first prototype of SPArc delivery on a clinical proton beam therapy machine and evaluated its delivery accuracy and efficiency.
Methods: A series of experiments was first performed to measure the basic beam characteristics under the arc delivery, including isocentricity, spot profiles, beam flatness and symmetry, and beam output. Subsequently, patient specific QA of a brain SPArc plan was performed to compare the measured and calculated dose distributions. Total SPArc treatment delivery time was also recorded and compared to the clinically delivered plan treatment time. Finally, the log file of the SPArc plan was analyzed and processed to reconstruct the actual delivered dose.
Results: All the basic beam characteristics, spot position accuracy within 1mm, spot size within +/-2%, beam flatness and symmetry within +/-3%, and output within 2% of the selected energies were confirmed within the clinical requirements in the arc delivery. The brain SPArc plan with similar or superior plan quality was delivered in 4 minutes compared to total 11 minutes for the clinical treatment of the three-field IMPT plan. The patient specific QA results showed a good agreement between the measured and calculated dose distributions for the brain SPArc plan with the gamma index of 98.6% (3%, 3mm). The analysis of the log file confirmed the accuracy of the SPArc plan delivery with the gamma index of 98.3% (1%, 1mm) between reconstructed and plan doses.
Conclusion: The first dynamic proton arc delivery on a clinical proton therapy system was successfully performed. The measurements and simulations demonstrated the feasibility of SPArc treatment within the clinical requirements.
Funding Support, Disclosures, and Conflict of Interest: Grant/Research Support: Beaumont Herb and Betty Fisher research seed grant award; Ion Beaumont Application Inc. (IBA) research funding; A patent related to the proton arc therapy is licensed to Ion Beaumont Application Inc.