Validation of Cardiorespiratory-Gated Proton Beam Delivery for Stereotactic Arrhythmia Radioablation

Stereotactic arrhythmia radioablation (STAR) is a promising noninvasive therapy for refractory ventricular tachycardia. Using scanned proton beams for STAR enables precisely focused, high doses of ionizing radiation. Effective mitigation of target motion is critical for safety but remains challenging due to the complex interplay between beam scanning and cardiorespiratory motion. We evaluated the safety and feasibility of accurately delivering gated scanned proton beams to a ventricular myocardial target and compared lesion outcomes of respiratory (single)- and cardiorespiratory (dual)-gated proton beams.

Six pigs (the first two used as a test of the protocol) underwent baseline CT for treatment planning with a single fractional dose of 35 Gy to a myocardial target in the left ventricular free wall. They were subsequently treated with either single- or dual-gated delivery using scanned proton beams. Treatment response was evaluated by echocardiography, blood analysis and positron emission tomography (PET)-CT at baseline and 14-15 weeks after irradiation. Lesions were assessed at termination, and tissues were harvested for histopathology.

Average target expansion for intrafractional motion was lower with dual compared to single gating (16%-23% vs. 48%-72%, N = 2 in each arm). The irradiated area was distinguishable in vivo on PET-CT and ex vivo in necropsy at the expected location in all animals. Visual lesion transmurality was confirmed by histology. Lesion sizes were not far from the expected volumes in dual-gated animals but were larger in single-gated animals (p = 0.3 for between-group comparison, N = 2 in each arm).

The results confirmed the feasibility of the workflow. Dual-gated irradiation was associated with reduced radiation exposure of the myocardium outside the target volume, and with lesion sizes closer to those planned.