Abstract: Indications for re-irradiation are increasing both for palliation and potentially curative attempts to achieve durable local control. This has been in part driven by the technological advances in the last decade including image-guided brachytherapy, volumetric-modulated arc therapy and stereotactic body radiotherapy. These enable high dose focal irradiation to be delivered to a limited target volume with minimal normal tissue re-irradiation. The European Society for Radiotherapy and Oncology (ESTRO) and the European Organisation for Research and Treatment of Cancer (EORTC) have collaboratively developed a comprehensive consensus on re-irradiation practices, aiming to standardise definitions, reporting, and clinical decision-making processes. The document introduces a universally applicable definition for re-irradiation, categorised into two primary types based on the presence of geometric overlap of irradiated volumes and concerns for cumulative dose toxicity. It also identifies “repeat organ irradiation” and “repeat irradiation” for cases without such overlap, emphasising the need to consider toxicity risks associated with cumulative doses. Additionally, the document presents detailed reporting guidelines for re-irradiation studies, specifying essential patient and tumour characteristics, treatment planning and delivery details, and follow-up protocols. These guidelines are designed to improve the quality and reproducibility of clinical research, thus fostering a more robust evidence base for future re-irradiation practices. The consensus underscores the necessity of interdisciplinary collaboration and shared decision-making, highlighting performance status, patient survival estimates, and response to initial radiotherapy as critical factors in determining eligibility for re-irradiation. It advocates for a patient-centric approach, with transparent communication about treatment intent and potential risks. Radiobiological considerations, including the application of the linear-quadratic model, are recommended for assessing cumulative doses and guiding re-irradiation strategies. By providing these comprehensive recommendations, the ESTRO-EORTC consensus aims to enhance the safety, efficacy, and quality of life for patients undergoing re-irradiation, while paving the way for future research and refinement of treatment protocols in the field of oncology.
