Hypercellularity Components of Glioblastoma Identified by High b-Value Diffusion-Weighted Imaging

Abstract

Purpose Using conventional MRI for target definition, glioblastomas may receive inadequate radiation dose coverage of the nonenhanced hypercellular subvolume. This study aimed to develop a technique to identify the hypercellular components of GB by using high b-value DWI and to investigate its relationships with the prescribed 95%- isodose volume (PDV) and progression-free survival (PFS). Methods Twenty-one patients with glioblastoma underwent chemoradiotherapy post-resection/biopsy. RT treatment planning was based upon conventional MRI. Pre-RT DWIs were acquired in 3 orthogonal directions with b-values of 0, 1000, and 3000 s/mm2. Hypercellularity volume (HCV) was defined on the high b-value (3000 s/mm2) DWI by a threshold method. “Nonenhanced” signifies regions not covered by the Gd-enhanced gross tumor volume (GTV-Gd) on T1-weighted images. The PDV was used to evaluate spatial coverage of the HCV by the dose plan. Association between HCV and PFS or other clinical covariates were assessed using univariate proportional hazards regression models. Results HCVs and nonenhanced HCVs varied 0.58-67 cc (median: 9.8cc) and 0.15-60 cc (median: 2.5cc), respectively. Fourteen patients had incomplete dose coverage of the HCV, of which 6 patients had 1+ cc HCV missed by the 95%-PDV (range: 1.01–25.4cc). Of the 15 patients who progressed, 5 progressed earlier, within 6 months post-RT, and 10 patients after. Pre-RT HCVs within recurrent GTVs-Gd were 78% (range: 65–89%) for the 5 earliest progressions but lower, 53% (range: 0–85%), for the later progressions. HCV and nonenhanced HCV were significant negative prognostic indicators for PFS (p < 0.002 and p < 0.01, respectively). The hypercellularity subvolume not covered by the 95%-PDV was a significant negative predictor for PFS (p < 0.05). Conclusions High b-value DWI identifies the hypercellular components of GB and could aid in RT target volume definition. Future studies will allow us to investigate the role of high b-value DWI in identifying radiation boost volumes and diagnosing progression.

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