NIMG-33. TUMOR GROWTH AND MRI TRAJECTORIES IN GRADE II AND III GLIOMA

INTRODUCTION The purpose of this work was to investigate the trajectory of tumor growth and multiparametric MRI characteristics in grade II and III gliomas leading up to the onset of new contrast enhancement or the expansion of FLAIR signal abnormality. METHODS Fifty-one grade II and III glioma patients (39 grade II, 12 grade III) underwent serial MR imaging at standard of care timepoints. Multiparametric MR imaging was performed and maps of the apparent diffusion coefficient (ADC) and percentiles (10th, 50th, 90th) from histograms of normalized signal intensities were calculated. Regions of Interest (ROIs) were defined for the entire T2/FLAIR lesion, and when present, the contrast-enhancing (CE) lesion. Serial imaging parameters were acquired for each of these ROIs. Linear rates of change were calculated for CE volume, T2/FLAIR volume, normalized T2 FSE intensity within the FLAIR volume, normalized T2/FLAIR intensity within the FLAIR volume, and normalized median, 10th percentile and 90th% ADC values within the FLAIR volume. RESULTS Thirty-nine patients progressed while on study (7 by CE growth, 32 by T2/FLAIR growth), and 12 patients remained stable, according to RANO criteria. In progressed patients, T2/FLAIR volume and T2 FSE intensity increased over time to progression. The rate of T2/FLAIR volume growth was significantly greater in progressed than stable patients (mean = .42, -.07 mL/week, respectively). The rate of normalized T2/FLAIR signal intensity change was also significantly different in progressed than stable patients (mean = -.002, .0035 mL/week). There were no significant interactions with grade or molecular subgroup by WHO criteria. Additionally, 44% (17/39) of progressed patients by RANO criteria were characterized as having stable disease by radiologic assessment. CONCLUSION Tumor volumes remain the gold standard for response assessment in lower grade gliomas and there exists a need for standardized measurement as visual assessment for determination of tumor status is inconsistent.