S2422
Physics - Radiomics, functional and biological imaging, and outcome prediction
ESTRO 2026
Jalmes 1 , Renaud De Crevoisier 1 , Maria A Zuluaga 2 , Oscar Acosta 1 , Anaïs Barateau 1 1 CLCC Eugène Marquis – INSERM - LTSI - UMR 1099, LTSI, University of Rennes, Rennes, France. 2 Data science department, EURECOM, Biot, France Purpose/Objective: Tumour hypoxia plays a central role in resistance to radiotherapy (RT) and chemotherapy, contributing to treatment failure and disease progression [1]. Quantifying hypoxia is therefore crucial for anticipating tumour response, adapting irradiation doses, and enabling personalised monitoring. The recent 1.5T MR-Linac, offers a unique opportunity to acquire longitudinal and quantitative MRI (qMRI) data during RT. This study aims to evaluate qMRI biomarkers to monitor prostate tumour evolution over time during MRI-guided RT. Material/Methods: In this study, nine patients with localised prostate cancer were treated with stereotactic body radiotherapy (SBRT) (5 × 8Gy, simulation performed one month before) on an Elekta Unity 1.5T MR-Linac. At each session, optimised qMRI sequences were acquired: T2w, T2* and DW (Diffusion Weighted) images with multi-b values (0;5;20;40;80;200;500s/mm2) and fat suppression (SPAIR), based on established MR-Linacprotocolsfrom another center [2]. Tumours were delineated by an expert radio-oncologist on T2w images and contours propagated on co-registered T2* and DW images.These acquisitions enabled the extraction of qMRI biomarkers within the tumour volume: the Apparent Diffusion Coefficient (ADC) expected to be inversely correlated with cell density [3], the hypoxia score (HS), and the T2* expected to be inversely correlated with Gleason score and aggressiveness [4].Particularly, to calculate the ADC and HS, an IVIM (IntraVoxel Incoherent Motion) model (Equation (1)) was used to perform a pixel-wise fitting with signal from multi b-values DW-MR sequence [5]: With fBV: fractional Blood Volume, D*: pseudo- diffusion coefficient, and signal s(b) from multi b- values DW-MR images. A pixel-wise fitting of an exponential decay was performed to calculate the T2*. The evolution of these qMRI biomarkers was computed from first to last session of irradiation. Results: Across all patients, a small increase in ADC values was demonstrated through treatment (+11%), suggesting a decrease in tumoral cellularity. A slight decrease in HS was found (-2%), suggesting a slight decrease in aggressiveness. Figure1 and 2 show the ADC and HS evolutions for each patient. Due to device or patient issues, some sessions were not irradiated (empty dots
Fig 2
Conclusion: Findings indicate that larger lung volume and higher calcification scores are independently linked to increased risk of radiation-induced pulmonary toxicity in breast cancer patients. Identified cut-offs (lung volume>1745 cc, MaxHU>232, Agatston>7.63) may aid early risk stratification and personalized monitoring. Validation in independent cohorts is warranted. The study was supported by the project “TETRIS” HORIZON-EURATOM-2023-NRT-01 Grant number:101166699. References: [1] A. Belardo, et al. Density and volume of cardiac calcifications detected on planning CT predicts cardiotoxicity after hypo-fractionated whole breast Radiotherapy. Radiotherapy and Oncology, Volume 211, 2025,111098, ISSN 0167- 8140, https://doi.org/10.1016/j.radonc.2025.111098. Keywords: Breast cancer, Lung Toxicity, Predictive modelling
Digital Poster 1158
Longitudinal evaluation of quantitative MRI biomarkers on a 1.5T MR-Linac during prostate radiotherapy Valentin Septiers 1,2 , Joséphine Colineaux 1 , Léo Le Bozec 1 , Jennifer Le Guévelou 1 , Manon Baty 1 , Julie Faucheux 1 , Christophe Fusel 1 , Clément Guibert 1 , Alice Le Jeanne 1 , Lucie Pelhate 1 , Maxime Yon 1 , Hervé Saint-
Made with FlippingBook - Share PDF online