High-Speed Proton Therapy In a Short Breath-Hold: A Clinically Feasible Framework for Fast, Motion-Robust Delivery for Lung Cancer Treatment
Abstract
Purpose
Proton therapy offers superior dose conformity compared with photon therapy but remains limited by long delivery times and sensitivity to respiratory motion, particularly for thoracic tumors. Delivering an entire proton field within a short breath-hold (5–10s) could substantially mitigate motion-related uncertainties. We present a clinically implementable framework for ultra-fast proton therapy using a commercial synchrocyclotron system (MEVION S250-FIT), achieving sub-10-second field delivery without mechanical modifications.
Methods
A three-component delivery optimization strategy was developed. First, a hybrid Shoot-Through (ST) and Bragg-Peak (BP) beam approach was implemented, combining high-energy ST beams at the tumor periphery with BP beams centrally. Eight non–small-cell lung cancer cases were replanned in RayStation 2024B using a validated MEVION beam model and compared with standard adaptive-aperture BP plans for target coverage, dose homogeneity, and organ-at-risk sparing. Second, conventional line-by-line spot sequencing was replaced with a nearest-neighbor scanning algorithm that minimizes lateral magnet travel by selecting the closest undelivered spot within each energy layer. Third, a simplified two-pulse dose feedback scheme replaced standard four-step regulation, delivering most of the charge in the initial pulse with a corrective second pulse to maintain dose accuracy. System log data from demonstration runs were analyzed to derive realistic timing parameters for energy switching, spot transitions, and charge delivery, which were incorporated into delivery-time simulations.
Results
The combined framework enabled full-field delivery in under 10s for all cases, representing over a 90% reduction in delivery time compared with conventional adaptive-aperture plans. Dosimetric quality was preserved, with minimal changes in dose homogeneity and comparable organ-at-risk sparing. Lateral scanning time was reduced by approximately 80%, while dose accuracy remained within ±2%.
Conclusion
Ultra-fast, motion-robust proton therapy within a short breath-hold is feasible on existing clinical systems. This framework enables practical sub-10-second field delivery for large lung tumors, improving treatment robustness, patient comfort, and clinical throughput.