NIMG-77. IMPACT OF POST-SURGICAL ENHANCING TUMOR VOLUME AND T2/FLAIR VOLUME ON THE SURVIVAL IMPACT OF BEVACIZUMAB IN NRG ONCOLOGY/RTOG 0825

Abstract

INTRODUCTION: RTOG 0825 randomized 621 newly-diagnosed glioblastoma patients to treatment with or without bevacizumab, in addition to standard-of-care radiotherapy plus concurrent/adjuvant temozolomide. No significant difference was seen between the treatment arms in overall survival (OS), and the difference in progression free survival (PFS) did not meet the pre-defined statistical margin. We evaluated the impact of post-surgical MRI-determined residual tumor on outcomes. METHOD(S): 431 (69.4%) patients had post-operative T1 MRIs (with and without gadolinium) and 517 (83.2%) had T2 or FLAIR images. Volumetric segmentation was performed to calculate residual enhancing (T1Gd-T1) volume (rEV) and T2/FLAIR volume (rT2FV). Multivariable analyses were performed using Cox models with pretreatment characteristics and treatment as covariates. RESULT(S): Median post-operative, pretreatment rEV was 2.8 cc (range 0.0-79.6 cc) and rT2FV volume was 52.3 cc (0.0-279. 8 cc). Neither age nor MGMT methylation were predictors of rEV or rT2FV. Ninety-four (21.8%) patients had an imaging-complete resection of enhancing tumor (rEV=0.0). We did not detect a significant difference in OS or PFS for an imaging-complete resection. Notably, however, a rEV