S2373
Physics - Quality assurance and auditing
ESTRO 2026
3 Cardiology, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom. 4 Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom. 5 Department of Neuroradiology, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom Purpose/Objective: Ventricular arrhythmias (VAs) are the most common cause of sudden cardiac death. Most VAs are triggered by the sympathetic nervous system via the stellate ganglia (1). Surgical removal of a portion of the stellate ganglia and sympathetic chain is an option in some patients. However, this procedure currently has high complication rates (2). Whether radiotherapy can be targeted at the stellate ganglia to reduce VA is unknown.We describe commissioning for the use of MR-guided ultra-hypofractionted radiotherapy to target the stellate ganglia and T1-T2 sympathetic chain as part of the RADIO STAR trial, a BHF-funded, first-in- man, phase 1 clinical trial (ISRCTN 49861434, REC:24/SC/0005). Material/Methods: Using anonymised volunteer scans, a planning exercise was performed on MR-Linac (ViewRay Systems MRIdian, Oakwood) and CT-Linac (Varian Truebeam, Palo Alto) systems for cross platform validation and backup planning. Planned prescription doses were 24 – 33 Gy in 3#.3D distortion was assessed on 1.5 T (Siemens MAGNETOM Avanto Fit, Forchheim) and MR-Linac scanners to quantify spatial integrity in the presence of cardiac device using a large field of view phantom (Large Field of View Distortion Phantom, CIRS, Norfolk, VA).Treatment plan deliverability and calculation accuracy was verified by 3D fluence and point dose measurements using suitable patient-specific quality assurance (PSQA) hardware (Sun Nuclear ArcCheck, Melbourne, FL). Results: Test plans showed target coverage of 43%-91%, depending on prescription dose, limited by brachial plexus dose guidance. Mean and maximum dose (D(2%) = 29 – 40 Gy) increased for each cohort. MR distortion was shown to be <2 mm in the region of the stellate ganglion and critical OARs. PSQA gamma pass rates were >98% at 3%/2mm and point dose difference <2%. In line with local institutional policies and national guidance, ICD doses were limited to D(0.05 cc) <5 Gy for all test plans. Conclusion: Planning and delivery is feasible across all dose levels on volunteer scans. MR distortion is sufficiently low to utilise for delineation. MR-guided stereotactic to the stellate ganglia radiotherapy is feasible and at the time of writing six patients have completed radiotherapy as part of the trial.
(SD: 0.01%) at 5%/2mm. BP GPRs were lower: 82%, 89%, and 95% for the same criteria.In inhomogeneous phantoms, FP maintained high accuracy (0.3% and 0.4% for 2 cm and 5 cm gaps), while BP deviations increased (1.5% and 2.3%). FP GPRs remained strong: 92%, 96%, and 99%, whereas BP dropped significantly: 63%, 72%, and 82%. BP variability was influenced by field size, phantom setup, and implementation; FP outliers were mainly linked to FFF fields.
Conclusion: This is the largest multicenter evaluation of EPID transit dosimetry accuracy to date. FP algorithms demonstrated robust performance in both homogeneous and inhomogeneous conditions, with minor limitations for FFF fields. BP algorithms achieved acceptable point dose accuracy but struggled with dose distribution, especially in heterogeneous media. Algorithm choice and implementation context are critical for clinical EPID dosimetry. References: 1) Esposito, M., Baldoni, R., Bossuyt, E., Bresciani, S., Clark, C. H., Jones, M., ... & Jornet, N. (2024). A commissioning protocol for portal imaging-based radiotherapy in vivo dosimetry systems. Physics and Imaging in Radiation Oncology, 32, 100666. https://doi.org/10.1016/j.phro.2024.100666 Keywords: EPID, in-vivo dosimetry, Poster Discussion 3030 Ultra-hypofractionated radiotherapy to the stellate ganglia for ventricular arrhythmia using MR-guided radiotherapy – pre-trial commissioning Ben George 1 , Maxwell Robinson 2 , Tom Whyntie 1 , Prabakar Sukumar 2 , Ebison Chinherende 1 , Benjamin Bussmann 3,4 , Fintan Sheerin 5 , Veni Ezhil 1 , Neil Herring 4,3 , Ami Sabharwal 1 1 Oncology, GenesisCare UK, Oxford, United Kingdom. 2 Medical Physics, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom.
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