ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S188

ESTRO 2025

Results: The expert group included 28 members from 10 countries (Europe, Canada and India). Results of the survey and first delineation round showed marked variation in treatment preparation as well as in definition and delineation of target volumes and OARs (Fig. 1). Consensus was reached on prerequisites for adequate delineation, i.e. required clinical information, timing and specifications for MR imaging and endoscopy, the use of clips, etc. The following target volumes were defined: GTV primary at the time of brachytherapy (GTVp_BT), a dose reporting structure representing GTVp_BT plus a 5mm margin (GTVp_BT+05), and any macroscopic lymph nodes at time of brachytherapy (GTVn) (Table 1A). Recommendations on OAR delineation are summarized in table 1B. Recommended structure naming followed AAPM TG-263.

Conclusion: The GI GEC-ESTRO working group has developed a consensus-based guideline for target volume definition and OAR delineation in HDR brachytherapy for rectal cancer. This guideline will be implemented in clinical practice and will be used to develop a guideline for dose reporting.