A Prospective Feasibility Study Evaluating Skin Surface-Guided Gating as a Method to Manage Intrafraction Motion for Stereotactic Body Radiotherapy on a Novel Ring Gantry Machine

Abstract

<h3>Purpose/Objective(s)</h3> We recently deployed CT-guided stereotactic body radiation therapy (SBRT) using an O-ring gantry linear accelerator with an artificial intelligence-enhanced treatment planning system capable of online adaptive radiotherapy. The intrafraction motion management solution for this system gates based on optical monitoring of the patient's skin surface. This system has not yet been clinically validated. Therefore, we prospectively evaluated the feasibility of surface-guided optical gating in a Phase I clinical trial for patients with mobile, upper abdominal or lower thoracic malignancies treated with SBRT on this machine. <h3>Materials/Methods</h3> Ten patients were planned for accrual to this study. Eligible patients were medically fit for SBRT, had at least one abdominal or thoracic disease site suitable for treatment, and were capable of breath hold for at least 17 seconds, the minimum duration of the on-board volumetric cone-beam CT. The trial protocol stipulated a treatment prescription in five fractions. Daily adaptation was at the discretion of the daily treating physician. MD arrival, re-contour, re-plan, delivery, and total fraction times were recorded. <h3>Results</h3> Eight patients enrolled and were eligible for evaluation at the time of this submission. Forty of 41 fractions (98%) were successfully delivered. One patient tolerated only partial delivery of his first fraction because of pain, but the remaining dose was successfully delivered in a sixth fraction. Twenty-seven fractions (53%) were adapted online, motivated by improving target coverage (7%), meeting organ constraints (33%), or both (44%). The median total fraction time was 80 minutes (IQR 66 – 96). <h3>Conclusion</h3> Skin surface-guided optical gating proved feasible in nearly all attempted fractions for respiratory gating of upper abdominal and lower thoracic tumors. This methodology is now being incorporated for SBRT on this platform off-trial.