ESTRO 2025 - Abstract Book

S1485

Clinical – Mixed sites & palliation

ESTRO 2025

A radiological outcome was noted in all 53 cases within 45 days. The most common imaging modality used was PET CT (n=53) and it showed a complete response in 41 cases, an interval reduction in size in 12 cases, and a significant decrease in activity in all 53 cases. All patients had < grade 2 skin toxicity. Genitourinary and gastrointestinal toxicities in 32 cases where it was applicable were < grade 2. Patients with painful metastasis (n=13) presented with a median pain score of 7 (range 3-8). After SBRT, the reported pain score dropped to a median value of 2 (range 0 8). No patient reported any adverse event. Conclusion: The CyberKnife is a versatile tool to deliver targeted radiotherapy to a variety of indications across various sites in the body. The low incidence of adverse events further emphasizes its value.

Keywords: CyberKnife, SBRT, Extracranial sites

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Digital Poster Early safety and efficacy results of a prospective dose de-escalation clinical trial of cardiac radioablation for ventricular tachycardia(NCT05258422) Ian J. Gerard 1 , Deepti Ranganathan 2 , Sarah Konermann 3 , Sara Vazquez-Calvo 2 , Valeria Anglesio 2 , Martin L. Bernier 2 , Tarek Hijal 1 , Neil Kopek 1 , Piotr Pater 4 , Gabriela Stroian 4 , Joanne Alfieri 1 1 Radiation Oncology, McGill University Health Centre, Montreal, Canada. 2 Cardiology, McGill University Health Centre, Montreal, Canada. 3 Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, Canada. 4 Medical Physics, McGill University, Montreal, Canada Purpose/Objective: Cardiac radioablation (CRA) is an emerging therapeutic option for refractory ventricular tachycardia (rVT). The standard CRA dose is 25 Gy in 1 fraction (fx), however, optimal therapeutic dosing isn't well established. This prospective, single-arm, phase 2, dose de-escalation clinical trial is the first to evaluate the safety and non-inferiority of 20Gy/1fx for managing rVT [1]. We report the early safety and efficacy of this protocol. Material/Methods: Eligible participants with monomorphic rVT unresponsive to standard medical therapy were offered participation in the study. Exclusion criteria included prior thoracic radiation therapy, active connective tissue disease, pregnancy, and interstitial pulmonary fibrosis. Participants were prescribed 20Gy/1fx to the arrhythmogenic substrate using volumetric modulated arc therapy with 3 coplanar arcs. Implantable cardioverter-defibrillators (ICD) were programmed at the physician’s discretion, with an anti -tachycardia pacing (ATP) zone set 20 milliseconds slower than the documented arrhythmia. Following CRA, a 6-week washout period was allowed where VT events were tracked but not included in efficacy analyses. Toxicity was graded using the common terminology criteria for adverse events (CTCAE) v5.0. A CT scan of the chest was performed at 3 months to evaluate for radiation pneumonitis. VT burden was defined as any sustained VT episodes requiring any ICD therapies. Results: Demographic and toxicity results are summarized in Table 1 for 5 participants with at least 6 months follow-up. The average planning target volume was 187.5cc (IQR 95.9 – 209.3). No grade 3 toxicity attributable to CRA has been observed. Grades 1 or 2 fatigue was experienced by 4 (80%) participants. Grade 2 esophagitis and Grade 2 pulmonary edema was observed in two separate participants. One participant died at 3 weeks following CRA from sepsis. The case was reviewed by the data monitoring and safety board and was deemed not related to CRA. Efficacy analysis of participants at 6 months shows 4 (80%) free of VT. Two (40%) participants had at least one event of VT, including one with VT storm during the 6-week washout period which stabilized without further events (Figure