Cardiorespiratory Motion Management for STAR with Ultra-High Dose Rate Proton Therapy
Abstract
Purpose
Stereotactic arrhythmia radioablation (STAR), a non-invasive treatment option for refractory ventricular tachycardia (VT), faces challenges from combined respiratory and cardiac motion, necessitating large target margins or motion mitigation. Respiratory gating and breath-holds are limited by low duty cycles that can significantly extend treatment times. We evaluate the feasibility of ultra-high dose rate (UHDR) proton therapy using a spread-out Bragg peak (SOBP) technique with a conformal energy modulator to enable beam delivery within a single breath-hold per field.
Methods
Five VT cases previously treated on linear accelerators (PTV range: 118-213cc) underwent retrospective replanning with UHDR protons on an IBA Proteus Plus system with the ConformalFLASH snout. Planning was performed on full-inspiration CT phase scans to represent breath-hold anatomy, prescribing 25 Gy in a single fraction. Plan quality metrics included target D98%, D2%, V95% and maximum doses to organs at risk (OARs) such as heart, stomach, and esophagus. Estimated delivery times were calculated via in-house Raystation scripting and validated through delivery logfile analysis.
Results
All plans were optimized using a combination of 2-4 proton fields. Target coverage was comparable to clinical photon intensity-modulated radiotherapy (IMRT) plan metrics, demonstrating average [D98%: 2365 cGy, D2%: 2957 cGy, V95%: 98.5%]. Average maximum doses to the heart, esophagus, and stomach were 3048, 631, and 894 cGy, respectively. Each field achieved high dose rates, enabling beam delivery times ranging from 0.46 to 1.29 seconds per field, well within single breath-hold capacity.
Conclusion
UHDR SOBP proton therapy successfully delivers conformal cardiac radioablation in approximately one second per beam. The reduction in motion uncertainties with ultra-fast delivery potentially enables margin reduction, toxicity reduction, and reirradiation feasibility for recurrent arrhythmias. This approach represents significant advances in treatment efficiency and geometric precision for STAR procedures.