S86
Brachytherapy - Gynaecology
ESTRO 2026
analysis for the CTV-App and CTV+App contouring techniques showed a non-significant difference in toxicity risk for bowel, rectum, and bladder, with respective increase of 0.14%, 0.04%, and 0.02%.
Digital Poster 4871
Dosimetric evaluation for CTV delineation in adjuvant vaginal cuff brachytherapy: impact of applicator inclusion Lisa Vicenzi 1 , Daniele Carlotti 1 , Valerio Marè 1 , Guenda Meffe 1 , Aurelia Iurato 1 , Lucrezia Toppi 1 , Claudia Tacconi 1 , Paolo Matteucci 1 , Sara Reina 1 , Roberta Guarnaccia 1 , Elisabetta Lepre 1 , Gian Marco Petrianni 1 , Gabriele D'Ercole 1 , Edy Ippolito 2,1 , Michele Fiore 2,1 , Sara Ramella 2,1 1 Operative Research Unit of Radiation Oncology, Fondazione Policlinico Campus Bio-Medico, Rome, Italy. 2 Research Unit of Radiation Oncology, Department of Medicine and Surgery, Università Campus Bio-Medico, Rome, Italy Purpose/Objective: Accurate delineation of the clinical target volume (CTV) is essential to ensure optimal dosimetric quality and treatment efficacy in adjuvant brachytherapy (BT) for gynecological malignancies. However, guidelines do not explicitly statewhether the endovaginal applicator should be included within the CTV during contouring. This study aimed to compare two CTV delineation approaches, including the applicator (CTV+Appl) or excluding it (CTV–Appl) to assess their effects on target coverage, dose distribution, and organs of interest exposure, as well as to estimate potential biological outcomes. Material/Methods: A retrospective dosimetric analysis was performed for 51 patients treated with adjuvant vaginal cuff brachytherapy between December 2024 and September 2025 at our institution, using Oncentra Brachy treatment planning system (v8.6.3). For each patient, two separate CTVs were contoured on post- implant images: CTV+Appl (including the applicator) and CTV–Appl (excluding the applicator, representing the clinical volume). Treatment plans were independently optimized for both contouring methods, applying identical dwell-time modulation, optimization objectives, and organs of interest dose guidance. Normal Tissue Complication Probability (NTCP) models, fitted by the Vienna group [1] using data from the EMBRACE-I study, were applied to estimate the risk of side effects. Clinically relevant endpoints with established dose–response relationships were selected, and both univariate and multivariate Cox proportional hazard models were used. Results: Across the 51 paired datasets, mean D90 and D95 were 100.9 ± 0.7% and 95.3 ± 0.2% for CTV+Appl, versus 95.3 ± 0.7% and 91.5 ± 0.9% for CTV–Appl, respectively. The mean difference in organs of interest doses between methods was 5.5 ± 0.5%. The NTCP
Conclusion: The inclusion of the endovaginal applicator within the CTV delineation not significantly alters dosimetric parameters, leading to apparent but misleading improvements in coverage indices and reduced correspondence with true vaginal wall dose. Excluding the applicator provides a more accurate representation of the irradiated tissue and ensures more reliable NTCP-based side effects predictions. NTCP analysis indicated no clinically relevant difference in predicted complication probabilities, but inclusion of the applicator produced an artificial overestimation of dose coverage and a reduction in the dose delivered to the biologically meaningful target tissue. These findings support standardizing CTV delineation protocols in adjuvant vaginal cuff brachytherapy to improve dosimetric consistency and clinical interpretation. Prospective validation in larger patient cohorts is warranted. Keywords: vaginal cuff, NTCP, contourig guidelines References: Ecker S, et al. EviGUIDE - a tool for evidence-based decision making in image-guided adaptive brachytherapy for cervical cancer. Radiother Oncol. 2023 Sep;186:109748. doi: 10.1016/j.radonc.2023.109748. Epub 2023 Jun 16. PMID: 37330055. Digital Poster 4878 DEFINITIVE IMAGE-GUIDED RADIOTHERAPY VS SURGERY IN MEDICALLY INOPERABLE EARLY-STAGE ENDOMETRIAL CANCER: A MATCHED COMPARATIVE STUDY Dina Najjari-Jamal 1 , Lucia Gomez Lavin 2 , Sergi Fernandez Gonzalez 2 , Milica Stefanovic 1 , Cristina Gutierrez Miguelez 1,3 , Andrea Slocker Escarpa 1 , Marc Juarez Lozano 1 , Daniel Aguiar Santana 1 , Pablo Araguas Mora 1
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