ESTRO 2025 - Abstract Book

S105

Invited Speaker

ESTRO 2025

institutions. The recommendations offer a practical framework for clinical use and highlight the need for continued research into advanced dose mapping techniques, improved deformable image registration, and robust, integrated uncertainty analysis in cumulative dose assessment workflow. Radiotherapy workflow considerations and recommendations on cumulative organ-at-risk dose constraints were beyond the scope of this work, and will require further attention in separate guidelines.

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Speaker Abstracts How to set up a multicentre reirradiation trial: Pre-trial QA and RT guideline development Lone Hoffmann 1,2 , Stine Overvad Fredaslund 1 , Mai Ehmsen 3 , Torben Schjødt Hansen 4 , Vladimira Horvat 5 , Maria Fulgsang Jensen 3 , Laura Patricia Kaplan 5 , Marianne Marquard Knap 1 , Lotte Holm Land 6 , Christina Larsen 7 , Mikkel Drøgemüller Lund 4 , Hanna Rahbek Mortensen 3 , Morten Nielsen 6 , Wiviann Ottosson 7 , Gitte Persson 7 , Cécile Peucelle 8 , Mette Pøhl 8 , Arpit Saini 5 , Hella Maria Brøgger Sand 9 , Tine Schytte 6 , Filippa Sundbye 7 , Weronika Maria Szejniuk 9 , Simon Nyberg Thomsen 1 , Ane Appelt 10 1 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 3 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 4 Department of Oncology, University Hospital of Southern Denmark, Vejle, Denmark. 5 Department of Oncology and Palliative Units, Zealand University Hospital, Næstved, Denmark. 6 Department of Oncology, Odense University Hospital, Odense, Denmark. 7 Department of Oncology, Copenhagen University Hospital - Herlev and Gentofte, Herlev, Herlev, Denmark. 8 Department of Oncology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark. 9 Department of Oncology, Aalborg University Hospital, Aalborg, Denmark. 10 Leeds Institute of Medical Research, University of Leeds, Leeds, United Kingdom Abstract: The number of patients referred to retreatment is increasing. A subgroup of these receives reirradiation type 1 or 2 according to ESTRO-EORTC guidelines[1]. However, guidelines on dose accumulation, treatment planning, and dose constraints are lacking, as well as correlation between cumulative delivered dose and clinical toxicity. In Denmark, the prospective multicentre trial CURE Lung (CUrative REirradiation) will evaluate high-dose reirradiation of thoracic tumours, including lung cancer recurrences, solitary lung metastases, or new primary lung cancer. It is based on strict guidelines for treatment planning, dose accumulation, and clinical follow-up. The trial aims for 500 patients in five years. The primary endpoint is grade 4-5 radiotherapy-related toxicity. Interim analyses will be performed after inclusion of 50, 100, 200, and 300 patients to evaluate the rate of radiotherapy related toxicity grade 4-5. Availability of digital 3D dose plan(s) from previous radiotherapy is mandatory for patient inclusion, and image registration must be performed to transfer the dose from previous CT-image to current CT-image. Cumulative dose constraints are based on the national NARLAL2 dose escalation trial (NCT02354274) and international literature on thoracic reirradiation. Organ-dependent values for α/β and dose scaling factors accounting for tissue recovery are pre-defined and based on literature. Prioritised constraints are set for all mediastinal structures, lungs, thoracic wall, and skin. Compromises on target coverage are accepted if necessary to respect OAR dose constraints. National guidelines must be used for OAR delineation. Patients must be treated using daily image guidance. Treatment adaptation is mandatory in case of anatomical changes. An RTQA group has been formed, consisting of physicists and physicians from all Danish radiotherapy centres. The group has set up an extensive and mandatory pre-trial QA programme. It consists of three tasks: 1) image registration and dose accumulation, 2) dose planning, and 3) OAR delineation. 1. There are currently no consensus guidelines on image registration and dose accumulation for reirradiation. A pre-trial study was set up to investigate the variability of rigid (RIR) and deformable (DIR) image registration and dose mapping based on RIR or DIR. Seven cases were distributed to each centre. OARs were delineated using AI-assisted segmentation on the CT-images of the previous and current treatment and