ESTRO, ESNR and EORTC consensus-based definition for MRI abnormalities after radiotherapy for intracranial central nervous system tumours.

Magnetic resonance imaging (MRI) is essential for post-treatment surveillance of patients with intracranial central nervous system (CNS) tumours. However, interpretation is often complicated due to post radiotherapy MRI abnormalities. Current literature demonstrates substantial heterogeneity in terminology and definitions used to describe these MRI abnormalities, limiting clinical decision-making and comparability across studies. To address this, an international multidisciplinary Delphi consensus was conducted within the Radiation Imaging and Neuro-Oncology Group (RING). Questionnaires were developed by the steering committee and distributed to experts in radiation oncology, neuroradiology, neuro-oncology, medical oncology, and neurosurgery. A three-round Delphi method was employed, with consensus defined as ≥ 75% agreement. Consensus was reached on the applicability and definitions with adoption of the term Treatment-Related Imaging Abnormality (TRIA). Clear definitions for potential and confirmed TRIA were established. Subcategorization based on imaging features all demonstrated high agreement. For consistent application of the framework minimal essential elements for MRI request forms were identified. The final consensus was endorsed by ESTRO, ESNR and EORTC. This Delphi consensus provides a standardized framework for MRI abnormalities following radiotherapy for intracranial CNS tumours. The framework aims to harmonize reporting, support clinical decision-making, and improve comparability in future neuro-oncology research. Central nervous system neoplasms - Radiotherapy - Magnetic resonance imaging - Delphi Technique - Treatment-Related Imaging Abnormality (TRIA).