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.