S1536
Interdisciplinary - Quality assurance and risk management
ESTRO 2026
and relevant OARs (spinal cord, brachial plexus, esophagus, trachea), with optional CTV delineation. For each centre, the dose prescription and contours were performed according to the local practice. Target and OAR delineations were compared using DICE coefficient (DSC), 95% Hausdorff (HD95) and median surface distances (MSD) relative to a consensus contour, limiting the comparison region to 3 cm above and below the superior and inferior border of the GTV. Fractionation schedules, margins, and SIB (simultaneous integrated boost) use were recorded. Results: A total of 12 centres participated. For the spine case, prescriptions ranged from 3×8-10 Gy to 5×6-7 Gy, with 4 centres using a SIB approach for the GTV. For the lung case 8×7.5 Gy was the dominant fractionation, while three centres would treat with more fractions (15×3.4Gy, 15×4Gy and 24×2.75Gy) due to the close proximity of the esophagus and the trachea. GTV delineation showed high degree of agreement for both cases (Figure 1), with one outlier (yellow contour), while CTV use was inconsistent (present in 60% of submissions), resulting in up to fivefold variation in total CTV volume for the spine case due to the SIB approaches. Despite availability of contouring guidelines, the largest discrepancies were observed for small-volume OARs adjacent to the PTV.
Substantial variation exists in fractionation schedules among Belgian centres, however variability in GTV, PTV delineation differences were within expected limits for both spine and lung cases. Although these findings demonstrate high quality of standard practice across Belgian RT centres, they highlights the importance for national consensus, peer-review processes, and standardized SBRT fractionation guidelines to ensure uniformity and reproducibility across institutions. Keywords: interobserver variability, SBRT, Poster Discussion 4004 Towards ESTRO’s recommendations for a minimum set of radiotherapy-specific Quality Indicators Cristina Garibaldi 1 , Aude Vaandering 2 , Amanda Cassie 3 , Gianfranco Brusadin 4 , Pierfrancesco Franco 5,6 , Jeremy Millar 7 , Kristi MacKenzie 8 , Chuck Mayo 9 , Barbara A Jereczek-Fossa 10,11 , Nuria Jornet 12 1 Unit of Radiation Research, IEO-European Institute of Oncology, IRCCS, Milano, Italy. 2 Department of Radiation Oncology, Cliniques Universitaires St Luc, Brussels, Belgium. 3 Dept. of Radiation Oncology, Dalhousie University, Dalhousie, Canada. 4 Radiation Oncology Department, Goustave Roussie, Paris, France. 5 Department of Translational Medicine (DIMET), University of Eastern Piedmont, Novara, Italy. 6 Department of Radiation Oncology, 'Maggiore della Carità' University Hospital, Novara, Italy. 7 School of Translational Medicine, Monash University, Melbourne, Australia. 8 Canadian Partnership for Quality Radiotherapy, Canadian Association of Provincial Cancer Agencies, Toronto, Canada. 9 Dept. of Radiation Oncology Physics, University of Michigan, Ann Arbor, USA. 10 Dept. of Oncology and Hemato- oncology, University of Milan, Milan, Italy. 11 Dept. of Radiation Oncology, IEO European Institute of Oncology IRCCS, Milan, Italy. 12 Servei de Radiofisica i Radioprotecció, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain Purpose/Objective: Ensuring equitable access to modern radiotherapy requires consistent treatment quality across centers. Robust Quality Indicators (QIs) are crucial for assessing compliance to standards and identifying improvement areas. Currently, no standardised European QI set exists, although individual countries have developed their own. To address this gap, we worked on establishing a consensus on a minimum set of QIs, enabling benchmarking and contributing to continuous quality improvement in radiotherapy services across Europe. Material/Methods: A multidisciplinary core group, including radiation
Conclusion:
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