ESTRO 2025 - Abstract Book

S1186

Clinical – Lower GI

ESTRO 2025

Conclusion: Immunomodulatory RT before surgery is feasible and safe. These results should strengthen the collaboration between surgeons and radiation oncologists, crucial to ensure the optimal implementation of such multidisciplinary protocols.

Keywords: Colorectal cancer, Preoperative RT, Safety

2002

Mini-Oral Habitat-based MRI radiomics for survival prediction in locally advanced rectal cancer treated with neoadjuvant chemoradiotherapy Yanqi Huang 1,2 , Xiaobo Chen 2 , Fan Yang 3 1 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands. 2 Department of Radiology, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Guangzhou, China. 3 The First School of Clinical Medicine, Zhejiang Chinese Medical University, Hangzhou, China Purpose/Objective: To develop and validate a radiomics-based approach using pre-treatment MRI T2WI for predicting disease-free survival (DFS) in locally advanced rectal cancer (LARC) patients who underwent neoadjuvant chemoradiotherapy followed by surgical resection. Material/Methods: We retrospectively collected MRI T2WI scans and clinical characteristics from 2 independent cohorts of LARC patients who received neoadjuvant chemoradiotherapy followed by surgery, totaling 624 patients. We developed a two-stage clustering habitat imaging framework analyzing the mesorectum on the pre-treatment MRI T2WI scans and their corresponding local entropy maps. The framework first performed individual-level clustering, where the mesorectum regions were over-segmented into superpixels, followed by population-level clustering to identify distinct subregions. A multiregional spatial interaction (MSI) matrix was constructed to capture the co-occurrence patterns among different subregions, from which 32 quantitative features were extracted. These MSI features were used to classify patients into two distinct imaging subtypes. The overall workflow the habitat imaging–based radiomics analysis is shown in Fig. 1. The prognostic value was evaluated using multivariate Cox regression analysis and validated in external cohort.