Volumetric Analysis Using Low-Field Intraoperative Magnetic Resonance Imaging for 168 Newly Diagnosed Supratentorial Glioblastomas: Effects of Extent of Resection and Residual Tumor Volume on Survival and Recurrence

BACKGROUND: Extent of resection (EOR) remains controversial in therapy for glioblastoma (GBM). However, an increasing number of studies favor maximum EOR as being associated with longer patient survival. Residual tumor volume (RTV) has also recently emerged as a prognostic factor. Low-field intraoperative magnetic resonance imaging (iMRI) has contributed to improve the EOR of GBM. The purpose of this study was to analyze the relationships between EOR/RTV and overall survival (OS)/progression-free survival (PFS) in patients with newly diagnosed GBM using low-field iMRI. METHODS: Adult patients who underwent surgery for newly diagnosed supratentorial GBM between 2000 and 2012 were retrospectively reviewed. Three-dimensional volumetric tumor measurements were made. Multivariate analysis was used to evaluate the relationships between EOR/RTV and OS/PFS. RESULTS: Of 168 patients, 126 (75%) died and 154 (91%) showed tumor recurrence. Median OS and PFS for patients with iMRI were 19.3 months (95% confidence interval, 15.4-23.7 months) and 9.5 months (95% confidence interval, 7.8-10.8 months). Median preoperative tumor volume was 37.0 cm(3) (interquartile range [IQR], 19.9-59.8 cm3). Median RTV was 0 cm(3) (IQR, 0-1.6 cm(3)). Median EOR was 100% (IQR, 96.2%-100%). In multivariate analysis, after controlling for age and Karnofsky Performance Status, EOR and RTV remained significantly associated with survival (hazard ratio, 1.56; P = 0.018) and recurrence (hazard ratio, 1.53; P = 0.013). Maximum RTV for survival was 3 cm(3). CONCLUSIONS: This volumetric analysis for low-field iMRI showed that both EOR and RTV were significantly associated with survival and recurrence. We determined a threshold RTV of 3 cm(3) as the maximum RTV associated with survival.