Early DCE-MRI changes and concurrent radiologic response after stereotactic radiosurgery for brain metastases: a prospective exploratory study

Conventional MRI may show limited or equivocal changes in the early period after stereotactic radiosurgery (SRS) for brain metastases. This study evaluated whether early dynamic contrast-enhanced MRI (DCE-MRI) changes at 4–8 weeks after SRS are associated with concurrent early radiologic response in brain metastases. This prospective, exploratory, lesion-level study included 17 brain metastases from 12 consecutive patients treated with single-session Gamma Knife SRS. DCE-MRI was performed before treatment and at 4–8 weeks after SRS using a 1.5-T MRI system. Quantitative parameters (Ktrans, Ve, Kep, and initial area under the concentration–time curve [iAUC]) were derived using the Tofts pharmacokinetic model, and semiquantitative parameters (upslope and initial gradient) were obtained from signal-intensity curves. Response was classified according to RANO-BM criteria. Pre-to-post changes, between-group differences in absolute change, and exploratory associations with response category were analysed using Wilcoxon signed-rank, Mann–Whitney U, and Spearman correlation tests, respectively. Benjamini–Hochberg false discovery rate correction was applied within each test family. Six lesions (35.3%) were classified as partial response and 11 (64.7%) as stable disease. Ktrans, Kep, and iAUC decreased significantly after treatment and remained significant after false discovery rate correction. Initial gradient decreased in the unadjusted analysis ( p = 0.044) but did not survive correction. Ktrans showed a greater absolute reduction in partial response than in stable disease in the unadjusted analysis ( p = 0.020), but no between-group comparison survived correction. Percentage changes in Ktrans (rho = − 0.553, p = 0.021) and upslope (rho = − 0.503, p = 0.040) were associated with concurrent early radiologic response in unadjusted analyses; no correlation finding survived correction. In a one-lesion-per-patient sensitivity analysis, the direction of the Ktrans difference was consistent with the lesion-level analysis. Early DCE-MRI changes were detectable within 4–8 weeks after SRS. Ktrans showed the most consistent unadjusted association with concurrent early radiologic response. These hypothesis-generating findings require validation in larger, adequately powered, and methodologically standardised cohorts before clinical application.