Assessment of irradiated brain metastases using dynamic contrast-enhanced magnetic resonance imaging

Introduction: The purpose of this study was to evaluate the effect of stereotactic radiosurgery (SRS) on cerebral metastases using the transfer constant (K _trans) assessed by dynamic contrast-enhanced (DCE) MRI. Furthermore, we aimed to evaluate the ability of K _trans measurements to predict midterm tumor outcomes after SRS. Methods: The study received institutional review board approval, and informed consent was obtained from all subjects. Twenty-six adult patients with a total of 34 cerebral metastases underwent T1-weighted DCE MRI in a 1.5-T magnet at baseline (prior to SRS) and 4-8 weeks after treatment. Quantitative analysis of DCE MRI was performed by generating K _trans parametric maps, and region-of-interest-based measurements were acquired for each metastasis. Conventional MRI was performed at least 16 weeks after SRS to assess midterm tumor outcome using volume variation. Results: The mean (±SD) K _trans value was 0.13±0.11 min^-1 at baseline and 0.08±0.07 min ^-1 after 4-8 weeks post-treatment (p<0.001). The mean (±SD) total follow-up time was 7.9±4.7 months. Seventeen patients (22 lesions) underwent midterm MRI. Of those, nine (41 %) lesions had progressed at the midterm follow-up. An increase in K _trans after SRS was predictive of tumor progression (hazard ratio=1.50; 95 % CI=1.16-1.70, p<0.001). An increase of 15 % in K _trans showed a sensitivity of 78 % and a specificity of 85 % for the prediction of progression at midterm follow-up. Conclusion: SRS was associated with a reduction of K_trans values of the cerebral metastases in the early post-treatment period. Furthermore, K _trans variation as assessed using DCE MRI may be helpful to predict midterm outcomes after SRS.