RADT-39. FLAIR EXTENDING BEYOND A QUADRANT (FEQ) OF THE CEREBRUM AS AN IMAGING BIOMARKER FOR STUDIES OF ACUTE RADIATION EFFECTS IN POST-RADIOSURGERY BRAIN METASTASIS PATIENTS

Abstract INTRODUCTION Significant variability exists in the use of corticosteroids for treating adverse radiation effects (ARE) after stereotactic radiosurgery (SRS) of brain metastasis (BM). Here, we assess the reliability of a quadrant-based magnetic resonance (MR) FLAIR assessment as an imaging biomarker for steroid-dependent ARE. METHODS We conducted a retrospective study correlating FLAIR hyperintensity and corticosteroid treatment in post-SRS BM patients. FLAIR was assessed at four axial levels along the rostral-caudal axis of the cerebrum, defined by easily identifiable landmarks (including the superior temporal line, third ventricle, temporal horn, and fourth ventricle). New, post-SRS FLAIR hyperintensity extending beyond a quadrant (FEQ, or 25%) of the cerebrum at any of the four levels was defined as FEQ positive. FEQ positivity was then correlated with steroid treatment initiated within a month of the MRI. RESULTS To determine intra- and inter-rater reliability of FEQ, MR images from 20 patients (10 FEQ+ and 10 FEQ-) were assessed by three clinicians (a radiation oncologist and two neurosurgeons) for FEQ positivity. These results showed an >85% intra- and inter-rater reliability (Cohen’s Kappa and Fleiss’ Kappa of 0.970 and 0.785, respectively, both p< 0.001). We tested the hypothesis that FEQ+ is associated with corticosteroid use post-SRS in an initial cohort of 40 patients. The sensitivity, specificity, positive predictive value, and negative predictive value of FEQ for corticosteroid treatment were 75.0%, 96.4%, 75.0%, and 90.0%, respectively. To validate these findings, we examined the association of FEQ and corticosteroid use in an independent cohort of 214 SRS-treated BM patients. The sensitivity, specificity, positive predictive value, and negative predictive value of FEQ for corticosteroid treatment in this validation cohort were 94.6%, 74.0%, 43.2%, and 98.5%, respectively. CONCLUSION FEQ is an imaging marker with high intra- and inter-rater reliability, with a high negative predictive value (90.0-98.5%) for steroid treatment in SRS-treated BM patients. These results lay the foundation for future studies of FEQ for research and clinical applications.