Qualitative Dynamic Contrast-Enhanced MRI Time–Intensity Curve Analysis for Differentiating Non-Progressive Treatment-Related Changes from Tumor Progression After Stereotactic Radiotherapy for Brain Metastases

Background: This exploratory study assessed whether qualitative dynamic contrast-enhanced MRI (DCE-MRI) time–intensity curves (TICs) differentiate non-progressive treatment-related changes (NPTRC) from tumor progression after stereotactic radiotherapy for brain metastases. Methods: Thirty-two patients with 51 treated lesions underwent DCE-MRI. Five neuroradiologists independently delineated a volume of interest and classified the resulting TIC as Type A–D. Longitudinal clinical and MRI follow-up provided the reference outcome, which was recorded before the TIC framework was finalized. An A/B versus C/D grouping was evaluated as a secondary exploratory analysis. Results: Thirty-five lesions were classified as NPTRC and 16 as tumor progression. All 17 Type A lesions were NPTRC, whereas all 13 Type C/D lesions showed progression. Type B was observed in 21 of 51 lesions (41.2%), including 18 NPTRC and 3 progressive lesions, representing a substantial indeterminate subgroup. The exploratory A/B versus C/D grouping yielded 81.3% sensitivity and 100% specificity. The ordinal TIC analysis yielded an AUC of 0.952. Interobserver agreement was high within the present reader group (Fleiss’ κ = 0.889). Conclusions: Type A was associated with NPTRC, Types C/D were associated with progression, and Type B represented an indeterminate pattern. These descriptive findings require independent validation before clinical use.