Room: Stars at Night Ballroom 1
Purpose: Spot scanning proton arc therapy (SPArc) is a novel form of intensity modulated proton therapy (IMPT) planning which can improve the plan quality, robustness, and plan efficiency. The purpose of this study is to incorporate the dose-averaged linear energy transfer (LETd)-based biological dose optimization into SPArc planning, and to exploit the benefits of using SPArc in proton therapy.
Methods: A fast Monte Carlo dose calculation engine (MCSquare) and a robust optimizer (MIROpt) for proton pencil beam scanning have been modified to incorporate LETd-based biological dose optimization for both multi-field IMPT and SPArc treatment planning. One prostate patient was selected for this study. SPArc plan and multi-field IMPT plans with beam configurations of 2, 4, 6, and 8 equally spacing fields were generated using the biological optimization to achieve similar dose distributions while maximizing the LETd in the target volume. The average LETd in the target volume and the estimated delivery time based on energy layer switch time of 0.6s were compared.
Results: With similar dose distributions, the average LETd in the target volume increased with increasing number of fields used. Specifically, the average value of LETd in the target volume was 4.38, 4.65, 4.85, 4.85, and 5.06 keV/Î¼m for 2, 4, 6, 8 fields IMPT and SPArc plans respectively. Compared with 2 field non-biologically optimized plan, the corresponding rise of LETd value was 21%, 29%, 34%, 34%, and 40% for the 2, 4, 6, 8 fields IMPT and SPArc plans respectively. The estimate delivery time for the 2, 4, 6, 8 fields IMPT and SPArc plans was 96, 150, 171, 188, and 125 second respectively.
Conclusion: This work demonstrates the feasibility and advantage of using SPArc for biological dose optimization. Hence SPArc has the most ability to optimize LET distribution which can potentially increase the tumor control.
Funding Support, Disclosures, and Conflict of Interest: A patent related to SPArc has been filed.