KEY POINTS
- This technical feasibility study adapted photon stereotactic arrhythmia radioablation workflows to proton therapy, integrating electroanatomical mapping-to-CT target transfer, proton treatment planning and accelerator-side cardiac gating for three refractory ventricular tachycardia cases from the STOPSTORM.eu benchmark.
- CARDIO-RT was used to transfer arrhythmogenic substrates from electroanatomical maps to the planning CT. Two experienced cardiologists judged all transferred targets clinically acceptable, although assessment was qualitative and no quantitative registration-error or interobserver metric was applied.
- Plans used pencil-beam scanning with three to four fields and a single-fraction strategy derived from the photon STAR benchmark. A 32 Gy(RBE) CTV boost was combined with a nominal PTV prescription around 25 Gy(RBE); achieved PTV D95 ranged from 23.3 to 23.9 Gy(RBE) and CTV(EP) D95 from 30.9 to 31.6 Gy(RBE).
- Target compromises were required when anatomy made full coverage incompatible with OAR constraints: stomach overlap affected case 1, LVAD-related artefact case 2, and coronary/pulmonary artery proximity case 3. Nevertheless, CTV(EP) D50 reached approximately 32 Gy(RBE) in all three cases, with no CTV hotspot above 33.5 Gy(RBE).
- Priority OAR constraints were met almost completely. The only priority-1 deviation was a 0.1 Gy(RBE) excess to the pulmonary artery in case 3; esophageal, bronchial, tracheal and most coronary exposures remained very low or negligible.
- Estimated beam-on time ranged from 13 min 42 s to 17 min 39 s, with total in-room time of approximately 38–43 minutes before adding gating.
- Accelerator-side beam interruption occurred within tens of microseconds, while the clinically relevant full gating chain remained below 30 ms. At typical respiratory velocities of 5–10 mm/s, this corresponds to an estimated latency-related positional error of roughly 0.15–0.30 mm.
CLINICAL TAKEAWAY
Proton STAR for refractory ventricular tachycardia now has a technically coherent workflow spanning electrophysiologic target transfer, treatment planning and cardiac gating. This remains a preclinical feasibility study, however: motion robustness, patient positioning, end-to-end validation and clinical outcomes still need to be established before proton STAR can be considered an alternative to photon-based cardiac radioablation.