Evaluation of absolute and normalized apparent diffusion coefficient (ADC) values within the post-operative T2/FLAIR volume as adverse prognostic indicators in glioblastoma

To evaluate the association of normalized and absolute ADC metrics with progression free survival (PFS) and overall survival (OS) in patients treated for glioblastoma multiforme (GBM). Fifty-two patients with preradiotherapy diffusion weighted imaging treated with post-operative chemoradiation for GBM were evaluated. Region of interest analysis for ADC metrics including mean and minimum ADC value (ADC(mean)) and (ADC(min)) was performed within the T2/FLAIR volume. Normalized ((N))ADC values were generated relative to contralateral white matter. PFS and OS were analyzed relative to ADC parameters using a regression model. Kaplan-Meier and Cox proportional hazards analysis with respect to ((N))ADC(mean), and ((N))ADC(min) was performed. A ((N))ADC threshold < 1.3 within the T2/FLAIR volume was analyzed with respect to PFS and OS. Regression analysis indicated that normalized ADC values provide the strongest association with PFS and OS. Kaplan-Meier analysis revealed a non-significant trend toward inferior PFS and OS associated with ((N))ADC(mean) < 1.7, and a significant decrement to PFS and OS associated with ((N))ADC(min) < 0.3. ((N))ADC(min) was a significant prognostic factor when taking into account age, performance status, and extent of resection. ADC thresholding analysis revealed that a retained volume of > 0.45 cc per mL FLAIR volume was associated with a trend toward inferior PFS and OS. In the post-operative, pre-radiotherapy setting, the ((N))ADC(min) is the strongest predictor of outcomes in patients treated for GBM. ADC thresholding analysis indicates that a large volume of normalized ADC value < 1.3 may be associated with adverse outcomes.