ESTRO 2025 - Abstract Book

S267

Brachytherapy - Gynaecology

ESTRO 2025

Conclusion: Application of MRIGABT according to the EMBRACEII protocol - frequent use of IC/IS application and systematic multi parametric treatment planning - enables target doses (CTV-T HR D90) of ≥90 Gy EQD 10 for the vast majority of patients while OAR doses can be reduced to evidence-based dose-volume constraints, showing an improvement compared to EMBRACEI. This applies for patients with no, limited, as well as distal parametrial extension at BT. It is expected that this widening of the dosimetric therapeutic window will consequently lead to improved clinical outcome.

Keywords: MR-IGABT, change of practice

3528

Proffered Paper Identifying regions at risk of treatment failure and residual disease in cervical cancer chemoradiotherapy : An adapted risk-score Mohammed A Abdul-Latif 1,2 , Amani Chowdhury 1,2 , Hannah Tharmalingam 1 , Yatman Tsang 3 , Peter Hoskin 1,2 1 Department of Clinical Oncology, Mount Vernon Cancer Centre, Northwood, United Kingdom. 2 Department of Cancer Sciences, University of Manchester, Manchester, United Kingdom. 3 Radiation medicine program, Princess Margaret Cancer Centre, Toronto, Canada Purpose/Objective: Locally advanced cervical cancer is managed with chemoradiotherapy and brachytherapy. Developing a prognostic model would help identify patients at risk of adverse outcomes. An example of such a model combines apparent diffusion coefficient (ADC) from diffusion weighted MRI (DWI) with Ktrans from dynamic contrast enhanced MRI (DCE) to generate a hypoxia score (Lyng formula, Figure 1.) 1 . We have adapted this model to incorporate deoxyhaemoglobin concentration (R2* from blood oxygen level dependant MRI (BOLD)) and changes in ADC and R2* throughout treatment to generate a risk-score (RS overall , Figure 1.). We assess this adapted risk-score in patients with residual disease at 3 months after treatment, and how it relates to brachytherapy dose distribution. Material/Methods: Patients receiving chemoradiotherapy for cervical cancer were imaged with functional MRI (including DWI, DCE and BOLD) before (S1) and at the end of treatment (S2). Tumour volumes were contoured on every image and split into anatomical regions, or blocks (Figure 2.). The adapted risk-score was applied to these blocks. The risk scores for patients with residual disease at 3 months after treatment were assessed. Brachytherapy dose distribution was examined in context of the anatomical blocks.