ESTRO 2025 - Abstract Book

S262

Brachytherapy - Gynaecology

ESTRO 2025

Prentice method, and DFS and overall survival (OS) estimated using Kaplan-Meier method. We conducted prognosis analyses of DFS using Cox models

Results: Between January-2016 and December-2021, 388 patients were treated by RCT and IGABT. Median follow-up was 54.8 months (3.3–104.0). 346 (89.2%) patients presented a squamous cell carcinoma. Staging according to 2018 FIGO classification was IIIC1 in 175 patients (45.1%) and IIIC2 in 213 patients (54.9%). PAL was performed in 212 patients (54.6%). Dose of external radiotherapy was 45Gy (43.2-55.0). Interstitial IGABT was performed in 130 patients (33.5%). Median High Risk Clinical Target Volume (HR-CTV) was 35.2cc (5.8-151.0cc); D90 eqD2Gy HR-CTV: 86.9Gy (46.6-106.2). D2cc bladder, rectum, sigmoid and bowel was 77.5Gy (44.6-98.5), 68.5Gy (44.3-85.2), 56Gy (43.4 78.3) and 54.3Gy (43.2-82.1) respectively. Median of total duration of treatment was 51 days (35-165). At 1 year, 3 years and 5years, cumulative incidence of local relapse/progression was 10.8% (7.9-14.2), 16.6% (13.0-20.6) and 17.8% (14.0-22.0) at 1, 3 and 5 years respectively; DFS was 75.8% (71.0-79.8), 55.3% (50.0-60.3) and 50.8% (45.2-56.2), respectively. In multivariate analysis, three factors were associated with a poor DFS: WHO score >0 (Hazard Ratio, HR=1.62; 95%CI, 1.16-2.27; p=0.02), FIGO IIIC2 (HR=1.52; 95%CI 1.12-2.06, p=0.005), large HR-CTV (compared to HR CTV<30cc, HR 30cc -43.5cc =1.21; 95%CI, 0.82-1.78; and HR HR-CTV > 43.5cc =2.06; 95%CI 1.45-3.01; p=0.0002); Adenocarcinoma histological type is at the limit of significance with a HR=1.52 (95% CI, 0.98-2.35; p=0.06). Conclusion: Our real life series of patients with Stage IIIC LACC treated with RCT and IGABT show an excellent local control. HR CTV is still one of the most important prognostic factors. Digital Poster Dose accumulation for gynecological reirradiation: Systematic review of methods and evidence for prepilot of decision tree in RetroCOSMOS study Yvette Seppenwoolde 1 , J Kamalnath 2 , Ankita Gupta 2 , Anjana Anil kumar 2 , Jeevanshu Jain 2 , Monica Serban 3,4 , Supriya Chopra 2 , Kari Tanderup 5,6 , Remi Nout 1 , Mischa Hoogeman 1 1 Department of Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 2 Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Homi Bhabha National Institute, Navi Mumbai, India. 3 Department of Radiation Oncology, University of Toronto, Toronto, Canada. 4 Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Canada. 5 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 6 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: Cervical cancer patients receiving reirradiation for oligorecurrence or oligometastasis may have retreatment with variety of irradiation techniques (BT, IMRT, VMAT, photons, etc.), with or without brachytherapy applicators, with time gaps between subsequent reirradiation treatments. These factors create significant anatomical changes and make it difficult to accurately track each voxel in space and over time. Additionally, varying methods of reporting dose further complicate dose addition. The purpose of this study is to develop a practical solution that provides estimates of accuracy of different methods of dose addition for various clinical scenarios. Material/Methods: First, a decision tree has been developed that classifies different methods for dose addition for different scenarios. The methods for each scenario range from full 3D deformable dose addition to algebraic addition of point doses. Factors that are considered for the decision tree are: modality (BT+EBRT, EBRT+EBRT or combinations), the time Keywords: HR-CTV, Disease-Free Survival, local control 3437