Imaging MRI biomarkers for diagnosing brain radionecrosis: focus on incomplete ring enhancement sign
A Ortiz, E Santana, J Perez-Beteta, R Ciervide, J Diamantopoulos, P Martin, JM Sepulveda, A Hernandez-Lain, C Tramblin, S Garcia-Duque, B Ocaña-Tienda, C Rubio, L Koren
Neuroradiology (2026) doi:0.1007/s00234-026-04096-4
MOLAB authors
Pérez Beteta, Julián. Ocaña Tienda, Beatriz. 
Abstract
Purpose Differentiating brain radionecrosis from recurrent metastases after radiotherapy remains challenging because no single imaging technique is definitive. This study evaluated the diagnostic accuracy of the incomplete ring enhancement sign (IRES) on contrast-enhanced 3D T1-weighted gradient-echo MRI (CE 3D T1 GRE) as a diagnostic sign of radionecrosis and analyzed associated morphologic features. Methods In this retrospective case-control study, 45 cases of radionecrosis were identified from an institutional database of 1,179 brain metastases consecutively treated with stereotactic radiotherapy (2015–2022). Ninety CE 3D T1 GRE examinations were reviewed in blinded fashion: 45 radionecrosis examinations and 45 matched pre-treatment-naïve metastases from the same patients. The presence of IRES was assessed, and diagnostic performance was calculated. Interobserver agreement was evaluated using Fleiss’s kappa. Fragmentation, satellite lesions, and lesion distribution were compared using chi-square