Comprehensive Dosimetric and Delivery Tradeoffs for Proton Dynamic Arc Therapy Vs. IMPT for Nasopharyngeal Irradiation
Abstract
Purpose
Recent Phase 3 trial literature provides evidence for IMPT as the standard-of-care treatment for oropharyngeal cancer. Proton dynamic arc therapy (DynamicArc) potentially offers further refinement of IMPT. The goal of this work was to compare DynamicArc versus IMPT for anatomically complex nasopharynx cases.
Methods
Eight patients were retrospectively planned using DynamicArc (1 each coplanar/noncoplanar partial arc, no range shifter) and compared to paired IMPT plans (4-6 fixed fields, 7.5cm range shifter). RayStation 2023B-generated plans shared contours/prescriptions and were robustly optimized/evaluated (±3.0mm setup,±3.5% range) with Monte Carlo dose calculation (0.5% uncertainty, 40,000ions/spot). Target D99% and OAR endpoints (Gy[RBE=1.1]) were compared with Wilcoxon signed-rank tests (p5Gy) for serial organs like the optic nerve and chiasm as well as reductions in mean (>10Gy) for lens. High-dose median LETd changes with DynamicArc were OAR-specific. Dose-LETd density maps showed differences in the low-dose/high- LETd and high-dose/low- LETd tails of the distributions, often with minimal changes in dosimetric endpoint. DynamicArc decreased spots/layers and beam-on time (6.7 vs 9.9min) with large time savings estimated when accounting for between-field room entry, gantry/couch repositioning, and post-move image verification for IMPT (6.7 vs 29.4min).
Conclusion
DynamicArc achieves improved coverage/OAR sparing, comparable LETd, and large time savings making implementation feasible.