ESTRO 2025 - Abstract Book

S103

Invited Speaker

ESTRO 2025

4819

Speaker Abstracts ESTRO Physics Working Group on Reirradiation: Consensus guidelines on cumulative dose evaluation in reirradiation Marija Popovic 1,2 , Piotr Andrezejewski 3 , Lone Hoffmann 4 , Colin Kelly 5 , Chrysanthi Michailidou 6 , Donna H Murrell 7 , Chris Pagett 8 , Daniel Portik 9,10 , Heidi S Rønde 11 , Monica Serban 12 , Natasa Solomou 13 , Christopher Thompson 8 , Eliana Vasquez Osorio 14 , Nicholas S West 15 , Ali Zaila 16 , Ane Appelt 8 1 Department of Medical Physics, The Ottawa Hospital, Ottawa, Canada. 2 Medical Physics Unit, McGill University, Montreal, Canada. 3 Department of Medical Physics, MedAustron, Vienna, Austria. 4 Department of Medical Physics, Aarhus University Hospital, Aaarhus, Denmark. 5 Department of Medical Physics, St Luke’s Radiation Oncology Network, Dublin, Ireland. 6 Department of Medical Physics, German Oncology Center, Limassol, Cyprus. 7 London Regional Cancer Program, London Health Sciences Centre, London, Canada. 8 Department of Medical Physics, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom. 9 European Organisation for Research and Treatment of Cancer, (EORTC) Headquarters, Brussels, Belgium. 10 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre, Maastricht, Netherlands. 11 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 12 Department of Medical Physics, Princess Margaret Cancer Centre, Toronto, Canada. 13 Department of Radiotherapy Physics, Norfolk and Norwich University Hospitals (NHS Fundation Trust), Norwich, United Kingdom. 14 Division of Cancer Sciences, The University of Manchester, Manchester, United Kingdom. 15 Department of Medical Physics, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom. 16 Biomedical Physics Department, King Faisal Specialist Hospital and Research Center (KFSHRC), Riyadh, Saudi Arabia Abstract: Background: The need for reirradiation is growing as cancer survival rates improve and evidence of its efficacy strengthens. Cumulative dose assessment remains challenging due to anatomical changes over time, radiobiological factors such as tissue response and recovery, and inconsistencies in methodology across institutions. Current clinical practices vary widely, with notable discrepancies in cumulative dose estimates reported across different institutions. This impacts clinical decisions and the interpretation of reirradiation trial data. To address these issues, ESTRO Physics Reirradiation Working Group developed consensus guidelines to standardize cumulative dose evaluation in clinical reirradiation practice. Methods: The writing group of 14 medical physicists and one radiation oncologist was formed after the 2022 ESTRO Physics Workshop . Through a structured expert discussion process and a two-step voting approach, consensus recommendations were developed to establish best practices. The group analyzed scenarios ranging from full three-dimensional (3D) dose summation to situations with incomplete historical treatment data and subpar image registration. Key discussion points included dose mapping methods (rigid and deformable image registration), radiobiological corrections for fractionation differences (e.g., EQD2/BED conversions), uncertainties, and the importance of documentation, quality control, and peer review. Drafted statements were distributed to the remaining 36 members of the ESTRO Physics Reirradiation Working Group for consensus voting, with ≥80% and ≥60% agreement considered as consensus within the writing (n=15) and larger (n=36) groups, respectively. The Figure illustrates the process of developing statements, refining them, and voting to build consensus. Results: The writing group developed 38 consensus statements covering aspects of cumulative dose evaluation, including: previous treatment data (6), anatomical changes (1), image registration (5), equieffective dose rescaling (5), evaluation dose metrics (3), specialized radiotherapy techniques/modalities (2), proton/heavy ion therapy (1), brachytherapy (5), pediatric growth considerations (1), palliative treatment (2), image guidance and delivered dose evaluation (1), time/resource constraints (2), documentation (1), communicating uncertainties (1), and quality assurance (2). The first round of voting by the writing group (16 respondents) achieved consensus on 34 statements. Four contentious statements were refined. Following further consolidation, 28 statements were distributed for review and vote to the remaining 34 members (19 responded), ensuring broader input. All 28 statements reached consensus.