STereotactic Arrhythmia Radioablation in Europe: critical structure contouring benchmark results of the STOPSTORM Consortium

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU Horizon Background/Introduction In patients with refractory ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) showed promising results for otherwise untreatable patients [1]. The STOPSTORM.eu project coordinates European efforts to clinically validate STAR. Purpose The primary goal of the critical structures benchmark study was to harmonize contouring of organs at risk (OAR) for STAR within the STOPSTORM.eu consortium. The results enable to refine protocols and guidelines to ensure treatment harmonization. Methods Three well-selected STAR cases [2] were provided for this benchmark and sent to all radiation oncology centres within the consortium. Every case had a contrast-enhanced cardiac-CT which was already deformed to the primary planning-CT to contour the OAR in detail. Every centre was asked to contour 31 OAR’s according to literature-based guidelines. The resulting structure sets were evaluated within VelocityTM 4.1. Results Twenty centres participated in the critical structure contouring benchmark. Contouring of the structures was performed with high accuracy according to the provided guidelines. The contours of common OAR’s in radiotherapy, such as the heart, lungs, stomach, oesophagus, bronchus, great vessels, and spinal canal were correctly contoured by all centres. In the substructures of the heart (chambers, valves, arteries, and nodes), deviations in the contours occurred more frequently, but no large systematic errors were found (see figure 1-2). The centres that already performed STAR treatments had markedly less difficulties with the contouring of the substructures. However, these structures do not have a consensus for treatment planning purposes and late toxicity but need to be contoured correctly for future analysis within the STOPSTORM project. Conclusion This large STOPSTORM.eu multi-centre critical structure benchmark study showed a high accuracy regarding standard critical structures. In the case of heart substructures some deviations occurred, which lead to new definitions for contouring these structures within the consortium. In addition, a close collaboration between radiation oncologist and cardiac electrophysiologist is recommended. Contouring of the aortic valve by all ce Heatmap of the different contours of the