Using DWI-MRI parameters from multi- B values acquisition and a histogram approach for assessment of early therapeutic response in glioblastoma

Abstract

Abstract Early evaluation of therapeutic response of GBM on imaging is limited by poor biological specificity of clinical MRI. Clinical DWI-MRI models assume diffusion is mono-exponential when derived from only two B-values, although it has been proven diffusion is multiexponential. Purpose: To assess the utility of quantitative diffusion MRI derived from multi B-value acquisitions in the assessment of treatment response. Methods: 13 patients were enrolled into our multicentre study. Imaging was performed pre-RT and mid-RT using a multi B-value acquisition. Histograms within ROIs defined by abnormal FLAIR signal. Changes in histogram percentile profiles were evaluated across the two timepoints and compared with RANO assessment. Results: Following treatment, 5 patients had PD, 4 SD and 4 CR. Patients with PD showed a histogram shift to the left across all models, in keeping with increased cellularity. Parameters DDC and f are the most predictive of PD against RANO assessment, and appear superior to ADC. Reduction in 75th centile (f) and 95th centile (DDC) are the most sensitive histogram metrics for predicting early PD. Discussion: This is the first study to use histogram analysis as a marker of early treatment response in GBM. Results suggest association between early changes in specific diffusion components and subsequent treatment response. Spatially-independent diffusion parameter comparisons provide unbiased sampling of tumour heterogeneity. Conclusion: Our preliminary data suggest differential changes in diffusion parameters early in treatment, and provide proof of principle for multi B-value analysis and spatially-independent longitudinal assessment of diffusion imaging for therapeutic assessment in GBM.