Key result
Dual cardiorespiratory gating cuts proton target volume expansion by an absolute ~45% vs respiratory-only gating.
Why the study?
Motion management remains a critical challenge in stereotactic arrhythmia radiotherapy for ventricular tachycardia ablation. While respiratory gating is established, cardiac gating requires a dedicated workflow and gating device.
Does dual cardiorespiratory-gated proton pencil-beam scanning using real-time ultrasound tracking (CardioKit) reduce target volume expansion and mitigate motion interplay compared to respiratory-only gating in a swine model of cardiac ablation?
Does dual cardiorespiratory-gated proton pencil-beam scanning using real-time ultrasound tracking (CardioKit) reduce target volume expansion and mitigate motion interplay compared to respiratory-only gating in a swine model of cardiac ablation?
This preclinical validation demonstrates that real-time ultrasound-guided cardiorespiratory gating with mid-spot proton beam pausing is feasible and cuts cardiac motion target expansion by 45%, potentially sparing healthy myocardium during non-invasive ventricular tachycardia ablation.
May inform motion management in proton cardiac ablation; leaves open translation to human VT therapy.
Background Stereotactic Arrhythmia Radiotherapy (STAR) offers a non-invasive alternative for ventricular tachycardia ablation, yet motion management remains a critical challenge. While respiratory gating is established, cardiac gating requires a dedicated workflow and gating device. Methods This study establishes and validates an end-to-end workflow for cardiorespiratory gated proton STAR in six healthy swine. Key innovations include a novel pencil-beam scanning (PBS) controller enabling mid-spot beam pausing and resumption, and the integration of CardioKit, an ultrasound-based image-guidance system for real-time soft-tissue tracking. The workflow was evaluated by comparing single-gated (respiratory only) and dual-gated (cardiorespiratory) delivery strategies, assessing system latency, dosimetric accuracy on dynamic phantoms, and motion tracking fidelity against 4D-CT benchmarks. Results The upgraded PBS system demonstrated a gate response latency of <550 µs, effectively mitigating interplay effects in dynamic phantom measurements through gated beam deliveries. CardioKit provided respiratory motion traces highly correlated with 4D-CT data (Pearson r > 0.97) and responded to arrhythmic events within 5 ms. In vivo , dual-gating restricted delivery to the diastolic window (70–100% R–R), which resulted in a reduction in the Internal Target Volume (ITV) expansion by a mean of 45% compared to single-gating (19% vs. 64%), thereby substantially sparing healthy myocardium. Although dual-gating increased total beam-on time, the mid-spot interrupt capability ensured robust dose accumulation without treatment aborts. Conclusion The workflow for imaging, treatment planning, and cardiorespiratory-gated beam delivery was viable for treating all six subjects. The PBS system responded to gating commands < 550 µs and CardioKit responded to irregularities in heartbeat in <5 ms. Cardiorespiratory gating enabled an average 45% reduction in target expansion due to cardiac motion. Comparison of CardioKit respiratory motion traces with respiratory 4D-CT yielded differences of 1.1-1.4 mm in total motion amplitude and 0.97-0.99 Pearson correlation factor. These findings are valuable for establishing a workflow for cardiorespiratory-gated STAR treatment with CardioKit.
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Depauw et al. (2026) studied Cardiac motion management in stereotactic arrhythmia radiotherapy (healthy swine model) (n=6). Dual-gated (cardiorespiratory) proton pencil-beam scanning (PBS) with CardioKit ultrasound guidance vs. Single-gated (respiratory only) proton pencil-beam scanning (PBS) with 4-split layer-by-layer repainting was evaluated on Cardiac target volume (CardTV) to Internal Target Volume (ITV) expansion (%) (MD -45%). Dual cardiorespiratory gating with CardioKit reduced mean Internal Target Volume expansion by 45% compared to respiratory-only gating (19% vs. 64%) in swine undergoing proton cardiac ablation.
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