BACKGROUND/PURPOSE: High doses to healthy cardiac substructures (CS) in stereotactic arrhythmia radioablation (STAR) raise concerns regarding potential treatment-induced cardio-toxicity. However, CS contours are not routinely created, hindering the understanding of the CS dose-effect relationships. To address this issue, the alignment of CS contouring was initiated within the STOPSTORM consortium. In this study, we developed and evaluated auto-contouring models trained to delineate CS and major vessels in ventricular tachycardia (VT) patients. METHODS: Eight centres provided standard treatment planning computed tomography (CT) and/or contrast-enhanced CT datasets of 55 VT patients, each including 16 CS. Auto-contouring models were trained to contour either large structures or small structures. Dice Similarity Coefficient (DSC), 95 % Hausdorff distance (HD95) and volume ratio (VR) were used to evaluate model performance versus inter-observer variation (IOV) on seven VT patient test cases. Significant differences were tested using the Mann-Whitney U test. RESULTS: The performance on the four chambers and the major vessels (median DSC: 0.88; HD95: 5.8-19.4 mm; VR: 1.09) was similar to the IOV (median DSC: 0.89; HD95: 4.8-14.0 mm; VR: 1.20). For the valves, model performance (median DSC: 0.37; HD95: 11.6 mm; VR: 1.63) was similar to the IOV (median DSC: 0.41; HD95: 12.4 mm; VR: 3.42), but slightly worse for the coronary arteries (median DSC: 0.33 vs 0.42; HD95: 24.4 mm vs 16.9 mm; VR: 1.93 vs 3.30). The IOV for these small structures remains large despite using contouring guidelines. CONCLUSION: CS auto-contouring models trained on VT patient data perform similarly to IOV. This allows for time-efficient evaluation of CS as possible organs-at-risk.

Collegium Medicum Faculty of Medicine WSB University Dąbrowa Górnicza Poland; 3rd Radiotherapy and Chemotherapy Department Maria Skłodowska Curie National Research Institute of Oncology Gliwice Poland; Department of Urology Comprehensive Cancer Center Medical University of Vienna Vienna Austria

Department for Radiation Oncology Charité Universitätsmedizin Berlin Berlin Germany

Department of Oncology University Hospital and Faculty of Medicine Ostrava Czech Republic

Department of Radiation Oncology Amsterdam UMC Location University of Amsterdam Amsterdam the Netherlands

Department of Radiation Oncology University Hospital of Zurich Zurich Switzerland

Department of Radiation Oncology University Medical Center Mannheim Medical Faculty Mannheim University of Heidelberg Mannheim Germany

Department of Radiation Oncology University Medical Center Schleswig Holstein Kiel Germany

Department of Radiotherapy Maria Skłodowska Curie National Research Institute of Oncology Gliwice Poland

Department of Radiotherapy Maria Skłodowska Curie National Research Institute of Oncology Gliwice Poland; Department of Oncology and Radiotherapy Faculty of Medicine Medical University of Gdańsk Gdańsk Poland

Department of Radiotherapy University Medical Center Utrecht Utrecht the Netherlands

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