ESTRO 2025 - Abstract Book

S682

Clinical - CNS

ESTRO 2025

1746

Poster Discussion A European Particle Network (EPTN) Systematic Review of MRI Alterations in the Brain Following Radiation Therapy: towards a Uniform Definition Lieselotte Lauwens 1,2 , Marvin F. Ribeiro 3,4 , Catharina M.L. Zegers 3 , Morton Høyer 5 , Semi Harrabi 6 , Alida A. Postma 7,4 , Esther G.C. Troost 8 , Carola Lütgendorf-Caucig 9,6 , Alberto Iannalfi 10 , Jonathan Frederik Carlsen 11,12 , Valentin Calugaru 13,14 , Hiska. L. van der Weide 15 , Claire Alapetite 13,14 , Malin Blomstrand 16 , Frank Paulsen 17 , Sarah Peters 18 , Dario Di Perri 19,20 , Alejandra Méndèz Romero 21 , Daniëlle B.P Eekers 3 , Maarten Lambrecht 1,2,20 1 Departement of Oncology, Laboratory of Experimental Radiotherapy, KU Leuven, Leuven, Belgium. 2 Departement of Radiation Oncology, University Hospitals Leuven, Leuven, Belgium. 3 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, University Medical Centre+, Maastricht, Netherlands. 4 Mental Health and Neuroscience research institute (Mhens) Faculty of Health Medicine and Life Sciences, Maastricht University, Maastricht, Netherlands. 5 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 6 Departement of Radiation Oncology Heidelberg Ion Beam Therapy, University Hospital Heidelberg, Heidelberg, Germany. 7 Department of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands. 8 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany. 9 MedAustron Ion Therapy Center, MedAustron, Wiener Neustadt, Austria. 10 Clinical department, Radiotherapy unit, National Center for Oncological Hadrontherapy, Pavia, Italy. 11 Department of Radiology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. 12 Department of Clinical Medicine, Copenhagen University, Copenhagen, Denmark. 13 Radiation Oncology Department, Institut Curie, Paris, France. 14 Orsay Proton therapy Center, Institut Curie, Orsay, France. 15 Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands. 16 Department of Oncology, Sahlgrenska University Hospital Gothenburg and the Skandion Clinic, Gothenburg, Sweden. 17 Clinic for Radiation Oncology, Eberhard-Karls University, Tuebingen, Germany. 18 Department of Particle Therapy, West German Proton Therapy, University Hospital Essen, Essen, Germany. 19 Department of Radiation Oncology, Cliniques universitaires Saint-Luc, Brussels, Belgium. 20 Particle Therapy Interuniversitary Center Leuven, University Hospitals Leuven, Leuven, Belgium. 21 Department of Radiotherapy, Erasmus MC Cancer Institute, Erasmus MC University Medical Center, Rotterdam, Netherlands Purpose/Objective: Magnetic resonance imaging (MRI) often demonstrates alterations following cranial radiotherapy (RT), which may result in clinical symptoms and diagnostic uncertainty, impacting treatment decisions. Following the widespread introduction of proton therapy (PT), concerns emerged regarding an increased incidence of MRI alterations following PT, due to uncertainties in relative biological effectiveness. This systematic review provides an overview of MRI alterations in the brain post-RT, explores differences between photon RT (XRT) and PT and focusses on assessment methods and definitions across studies. Material/Methods: In accordance with the PRISMA guidelines, a search was conducted across three electronic databases using the concepts ‘radiotherapy’, ‘MRI alterations’ and ‘brain, skull base and head and neck tumours’. Studies reporting on MRI alterations after normo-fractionated RT in adult and paediatric populations were included, while studies on diagnosis and treatment of MRI alterations were excluded. Two independent reviewers performed data extraction and quality assessment on articles meeting predefined criteria. Results: Out of 5887 screened studies, 94 were included. These studies were categorized based on confinement of MRI alterations to temporal lobe, brainstem, or across the entire brain. Additional subclassification was performed based on MRI sequences evaluated or by the nature of the alterations, with pseudoprogression generally reserved for glioma patients. Figure 1 illustrates the heterogeneity in definitions across a subset of included categories, while figure 2 shows the incidence of MRI alterations across these studies. A meta-analysis to determine the incidence of