NIMG-15. RAPID EARLY PROGRESSION AFTER SURGERY ON PRE-RADIATION PLANNING MRI FOR IDH-WILDTYPE GLIOBLASTOMA

Abstract BACKGROUND Use of pre-RT planning MRI for glioblastoma (GBM) is inconsistent and not required by many clinical protocols. We performed a detailed volumetric analysis of rapid early progression (REP) on pre-RT planning MRI’s, hypothesizing that REP is associated with worse survival and more accurately risk stratifies than extent of resection. METHODS Patients with IDHwt GBM who had resection (biopsy-only patients excluded) and pre-RT planning MRI ≥2 weeks after postop MRI were included. MRI’s were reviewed by a neuroradiology fellow and attending who measured in 3 dimensions new/increased contrast-enhancing disease between postop and pre-RT MRI. REP was defined as disease ≥1cm in 2 dimensions or ≥0.5cc. Extent of resection was scored 1: gross total (GTR, >95%); 2:near total (NTR, 90-95%); 3:subtotal (STR). The primary endpoint was survival (OS). Cox proportional hazards model analyzed association with age, resection extent, MGMT+ status, short course RT (a surrogate for performance status), and REP. RESULTS The final cohort included 77 patients (median age 63), with 9 (12%) receiving short course RT. Surgical extent was GTR in 42 (55%), NTR in 16 (21%), and STR in 19 (25%). REP occurred in 41 patients (53%), with a rate of 29% after GTR, 75% after NTR, and 90% after STR. Age (p=0.24, HR 1.02/yr), short course RT (p=0.64, HR 1.2), and surgical extent (p=0.49, HR 1.1) were not significantly associated with OS on univariate analysis. MGMT+ and REP were associated with survival on both univariate and multivariate (MGMT+ p=0.002, HR 0.4; REP p=0.005, HR 2.3) analyses. Median OS was 1.3 years vs. 1.9 years with vs without REP. CONCLUSIONS REP occurs frequently, adds a “growth rate” variable, and is a better prognostic factor than extent of resection. These data have implications for clinical trial design and support pre-RT planning MRI’s as standard of care.