Diffusion MR Characteristics Following Concurrent Radiochemotherapy Predicts Progression-Free and Overall Survival in Newly Diagnosed Glioblastoma.

The standard of care for newly diagnosed glioblastoma (GBM) is surgery, then radiotherapy (RT) with concurrent temozolomide (TMZ), followed by adjuvant TMZ. We hypothesized patients with low diffusivity measured using apparent diffusion coefficient (ADC) histogram analysis evaluated after RT+TMZ, prior to adjuvant TMZ, would have a significantly shorter progression-free (PFS) and overall survival (OS). To test this hypothesis we evaluated 120 patients with newly diagnosed GBM receiving RT+TMZ followed by adjuvant TMZ. MRI was performed after completion of RT+TMZ, prior to initiation of adjuvant TMZ. A double Gaussian mixed model was used to describe the ADC histograms within the enhancing tumor, where ADC and ADC were defined as the mean ADC value of the lower and higher Gaussian distribution, respectively. An ADC value of 1.0 um/ms and ADC value of 1.6 um/ms were used to stratify patients into high and low risk categories. Results suggest patients with low ADC had significantly shorter PFS (Cox Hazard Ratio = 0.12, P = 0.0006). OS was significantly shorter with low ADC tumors, showing a median OS of 407 vs. 644 days (Cox Hazard Ratio = 0.31, P = 0.047). ADC was not predictive of PFS or OS when accounting for age and ADC. In summary, newly diagnosed glioblastoma patients with low ADC after completion of RT+TMZ are likely to progress and die earlier than patients with higher ADC. Results suggest ADC histogram analysis may be useful for patient risk stratification following completion of RT+TMZ.