ESTRO 2025 - Abstract Book

S3798

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2025

Conclusion: This study verifies the spatial correlation of CEBL with increased proton RBE and supports elevated PVR radiosensitivity in both proton and photon radiotherapy. These findings emphasize the need to consider ventricular proximity as a critical organ-at-risk and suggest incorporating variable proton RBE in treatment planning.

Keywords: brain lesions, proton RBE, periventricular region

References: [1] Bahn E, et al. Late contrast enhancing brain lesions in proton-treated patients with low-grade glioma: clinical evidence for increased periventricular sensitivity and variable RBE. Int J Radiat Oncol Biol Phys 2020;107:571–8. https://doi.org/10.1016/j.ijrobp.2020.03.013. [2] Eulitz J, et al. Increased relative biological effectiveness and periventricular radiosensitivity in proton therapy of glioma patients. Radiother Oncol 2023; 178. https://doi.org/10.1016/j.radonc.2022.11.011.

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Digital Poster A technical framework aiding quantitative evaluations of contrast-enhanced T1-weighted MRI after proton therapy: a feasibility study on meningioma Giulia Fontana 1 , Sithin Thulasi Seetha 1,2 , Giulio Di Ciaccia 1 , Sara Imparato 1 , Sara Lillo 1 , Alessia Bazani 1 , Alberto Iannalfi 1 , Ester Orlandi 2,1 1 Clinical Department, (CNAO) National Center for Oncological Hadrontherapy, Pavia, Italy. 2 Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy Purpose/Objective: Post-contrast T1-weighted (enhanced-T1) Magnetic Resonance Imaging (MRI) and dimensional lesion modifications are evaluated to identify relapses after Intensity Modulated Proton Therapy (IMPT). Although representing a great opportunity for a better understanding of treatment response, quantitative follow-up radiological reporting significantly increases radiologists’ workload. Our study aimed to design and evaluate the feasibility of a semi automatic technical framework to aid radiological quantitative reporting of the response pattern in meningioma patients (mng) undergoing IMPT. Material/Methods: 83 mng gross tumor volumes (GTV) were used to train a three-dimensional full-resolution nnUNet model [1] for lesion auto-contouring, based on T2-weighted and enhanced-T1 MRI sequences acquired before IMPT. Available follow-up enhanced-T1 of patients’ reporting local relapses were retrieved, along with a randomly selected consistent sample of control patients’ exams. Follow-up enhanced-T1 sequences were rigidly registered to the pre treatment enhanced-T1, and lesions automatically segmented. Hence, enhanced-T1 were rescaled with respect to brain tissues and kmeans clustering algorithm was used to automatically derive three contrast enhancement regions within the GTV and the follow-up segmented lesions. Finally, whole lesion and enhanced-region volumes, along with the respective enhanced-T1 values were computed and integrated in a quantitative follow-up report. Mann-Whitney U-test (α=0.05) was used to explore the effectiveness of the computed metrics (normalized on pre treatment GTV values) in describing follow-up relapses, as well as their predictive value.