Temporal evolution of MRI findings and survival outcomes in patients with brain metastases after stereotactic radiosurgery.

Objective: This study aims to investigate the temporal evolution of magnetic resonance imaging (MRI) findings in brain metastases following stereotactic radiosurgery (SRS) and their correlation with treatment response and survival outcomes. By analyzing volumetric changes in tumor size, perilesional edema, and necrotic components, we seek to identify imaging biomarkers that predict prognosis and treatment efficacy.

Methods: A retrospective analysis was conducted on 97 patients (200 metastatic lesions) who underwent SRS for brain metastases between 2010 and 2022. Multiparametric MRI (MPMRI) scans were analyzed at four distinct follow-up periods: 1 to 3 months, 3 to 8 months, 8 to 16 months, and 16 to 24 months post-SRS. Volumetric measurements of tumor size, perilesional edema, and necrosis were obtained using semi-automated segmentation. Apparent diffusion coefficient (ADC) values and relative cerebral blood volume (rCBV) ratios were also assessed. Statistical analyses, including Kaplan-Meier survival curves and ROC analysis, were performed to determine prognostic imaging biomarkers.

Results: The most significant reduction in tumor and perilesional edema volume occurred within the first 1 to 3 months post-SRS and continued until the 8th month. A transient increase in lesion size (pseudoprogression) was observed in 31.5% of cases, predominantly between 3 and 8 months post-SRS. Pretreatment tumor volume was found to be significantly associated with treatment response. ROC analysis identified 1.22 cm³ as the optimal cutoff value for differentiating between Group A (good response) and Group B (poor response) lesions (AUC = 0.754, sensitivity = 87.0%, specificity = 57.1%). Survival analysis revealed that higher pretreatment tumor volume, larger necrotic volume, and extensive perilesional edema were associated with shorter survival times (p < 0.05). No significant association was found between survival and ADC or rCBV.

Conclusion: Following SRS, early reductions in tumor and edema volume were observed, while 31.5% of cases showed transient enlargement. Smaller tumors responded better to SRS, whereas larger volume, extensive edema, and necrosis were linked to shorter survival. Given the high rate of pseudoprogression, not every post-treatment size increase indicates true progression. A wait-and-see approach may help avoid unnecessary interventions in selected cases.

Clinical trial number: Not applicable.