ESTRO 2025 - Abstract Book

S817

Clinical - Gynaecology

ESTRO 2025

Oncology Ljubljana, Ljubljana, Slovenia. 6 Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Homi Bhabha National Institute, India. 7 Department of Oncology, Cross Cancer Institute and University of Alberta, Edmonton, Canada. 8 Department of Radiation Oncology, Amsterdam UMC, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands. 9 Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam, Rotterdam, Netherlands. 10 Department of Radiotherapy, North Estonia Medical Centre Foundation, Tallinn, Estonia. 11 Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands. 12 Department of Radiotherapy, Radboud university medical center, Nijmegen, Netherlands. 13 Department of Oncology, Cambridge University Hospitals NHS Trust, Cambridge, United Kingdom. 14 Department of Oncology, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom. 15 Department of Oncology, Rigshospitalet, Copenhagen, Denmark. 16 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. 17 Department of Radiation Oncology, Pamela Youde Nethersole Eastern Hospital, Hong Kong, Hong Kong. 18 Department of Radiation Oncology, Institute Gustave Roussy, Villejuif, France Purpose/Objective: To describe and analyse external beam radiotherapy (EBRT) target volumes and to assess tumour regression after EBRT, stratified by TNM T-stages in patients with locally advanced cervical cancer (LACC). Material/Methods: The EMBRACE II study [1] is an international, prospective, single-arm cohort study investigating radiochemotherapy in LACC, focusing on image-guided adaptive brachytherapy (BT) and a defined EBRT target volume protocol for IMRT/VMAT. This protocol specifies the delineation of gross tumour volume(s) (GTV-T, GTV-N), high-risk clinical target volume (CTV HR -T), low-risk clinical target volume (CTV LR -T), and a risk-adapted elective nodal clinical target volume (CTV-E), which includes different cranial borders based on nodal metastasis risk (see EMBRACEII-protocol (appendix) [2]). An internal target volume (ITV45Gy) is based on the CTV LR -T and CTV-E, while a surrounding planning target volume (PTV45Gy and PTV-N) is also outlined (5 mm margin). Data were collected from 1482 patients treated across 49 centres between 2016 and 2021. Target volumes were quantified by median and interquartile range (IQR) in cm³. GTV-T regression following EBRT was measured in absolute volume (cm³) and percentage. Results: Among 1376 eligible patients with median age of 51 years (range 24-89), stage distribution was: T1b1 (7%), T1b2 (7%), T2a1 (2%), T2a2 (3%), T2b (66%), T3a (1%), T3b (11%), and T4 (3%). N0 cases accounted for 45%, and N+ for 55%, with 9% having para-aortic node involvement. Median and IQR for GTV, CTV HR , CTV LR , and ITV45Gy were documented pre-EBRT and at BT for the overall population and by T-stage (Table 1).