Arterial Spin Labeling Perfusion MRI Differentiates Between Radiation Necrosis and Tumor in Brain Metastases Treated with Stereotactic Radiosurgery

Accurate differentiation between radiation necrosis (RN) and tumor in brain metastases (BM) treated with stereotactic radiosurgery (SRS) can be challenging, but it is important because an accurate diagnosis impacts clinical management. In this study, we evaluated the utility of arterial spin labeling perfusion MRI (ASL-MRI) to accomplish this task.

We retrospectively evaluated 45 patients with 52 previously irradiated BM who had ASL-MRI prior to surgical resection. Histopathology served as the ground truth diagnosis of tumor and RN. Maximum cerebral blood flow (CBF) values were obtained within the contrast-enhancing lesions of interest and the pons (for normalization) on quantitative ASL-MRI CBF maps. In a subgroup analysis, patients with both pre-SRS and post-SRS ASL-MRIs were included, and CBF values were obtained at both timepoints.

Compared with RN, tumor had increased mean absolute and normalized CBF (P < 0.0001). In the subgroup analysis of patients with pre-SRS and post-SRS ASL-MRIs, change in absolute CBF (∆CBF) and normalized CBF (∆nCBF) of tumor showed higher absolute and percent differences between both timepoints (P < 0.02). Performance of ∆CBF and ∆nCBF (AUROC 0.80-0.89) acquired from two ASL-MRIs was comparable but not superior to CBF and nCBF (AUROC 0.90) acquired from single timepoint post-SRS ASL-MRI.

Increased CBF, whether absolute or normalized, on post-SRS ASL-MRI performed well to differentiate tumor from RN in BMs treated with SRS. Addition of pre-SRS CBF measurements did not improve the performance. ASL-MRI is a promising imaging tool to distinguish RN from tumor in this patient population.