ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S187

ESTRO 2025

Center, Medical University/General Hospital of Vienna, vienna, Austria. 6 Department of Radiotherapy of Oncology, University of Frankfurt, Frankfurt, Germany. 7 Department of Radiooncology, Helios Klinikum Erfurt, University Campus of Health and Medical University, Erfurt, Germany. 8 Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India. 9 Department of Radiation Oncology, HBNI University, Mumbai, India. 10 Fondazione Policlinico, Universitario Agostino Gemelli IRCCS, Rome, Italy. 11 Department of Radiation Oncology, NKI-AVL, Amsterdam, Netherlands. 12 Department of Radiotherapy, Erasmus Medical Center, Rotterdam, Netherlands. 13 Department of Radiotherapy, Leiden University Medical Center, Leiden, Netherlands. 14 Brachytherapy Department, Saint John’s Cancer Center, Lublin, Poland. 15 Radiotherapy Department, Medical University of Lublin, Lublin, Poland. 16 The Clatterbridge Cancer Centre, The Clatterbridge Cancer Centre NHS Foundation Trust, Liverpool, United Kingdom. 17 Department of Oncology, Royal Surrey Hospital, Guilford, United Kingdom. 18 Department of Oncology, University of Surrey, Guilford, United Kingdom Purpose/Objective: Lack of international guidelines is hampering treatment quality and progress in the field of HDR rectal brachytherapy. Standardization of dose reporting would allow for better comparison of clinical results between patient cohorts and also allow for normal tissue complication probability (NTCP) or tumor control probability (TCP) modelling. A prerequisite for standardized dose reporting is standardization of target volume and organ at risk (OAR) delineation. The GI GEC-ESTRO working group aims to develop and implement three consensus-based guidelines: 1) Target volume definition and OAR delineation; 2) Dose reporting; 3) Recommendations on patient selection, treatment preparation, dose prescription, treatment planning, and follow-up. The current abstract reports on the development of the guideline for target volume definition and OAR delineation. Material/Methods: The guideline has been developed according to the AGREE II instrument, using a modified Delphi approach (Fig. 1). The development process included selection of international expert radiation oncologists, physicists and RTTs (the expert group), a survey on current practices in target volume and OAR delineation, online delineation of three patient cases by radiation oncologists, and a first consensus meeting to discuss the findings and to draft a first version of the guideline. The 1st draft guideline was updated based on a 2nd delineation round and a consensus meeting. A review group, consisting of radiation oncologist who were not previously involved, reviewed the 2nd guideline draft. Subsequently, the expert group participated in a 3rd consensus meeting to draft the final guideline.