Diffusion-weighted endorectal MR imaging at 3T for prostate cancer: correlation with tumor cell density and percentage Gleason pattern on whole mount pathology

Objective: To determine if tumor cell density and percentage of Gleason pattern within an outlined volumetric tumor region of interest (TROI) on whole-mount pathology (WMP) correlate with apparent diffusion coefficient (ADC) values on corresponding TROIs outlined on pre-operative MRI.

Methods: Men with biopsy-proven prostate adenocarcinoma undergoing multiparametric MRI (mpMRI) prior to prostatectomy were consented to this prospective study. WMP and mpMRI images were viewed using 3D Slicer and each TROI from WMP was contoured on the high b-value ADC maps (b0, 1400). For each TROI outlined on WMP, TCD (tumor cell density) and the percentage of Gleason pattern 3, 4, and 5 were recorded. The ADC_mean, ADC_{10th percentile}, ADC_{90th percentile}, and ADC_ratio were also calculated in each case from the ADC maps using 3D Slicer.

Results: Nineteen patients with 21 tumors were included in this study. ADC_mean values for TROIs were 944.8 ± 327.4 vs. 1329.9 ± 201.6 mm²/s for adjacent non-neoplastic prostate tissue (p < 0.001). ADC_mean, ADC_{10th percentile}, and ADC_ratio values for higher grade tumors were lower than those of lower grade tumors (mean 809.71 and 1176.34 mm²/s, p = 0.014; 10th percentile 613.83 and 1018.14 mm²/s, p = 0.009; ratio 0.60 and 0.94, p = 0.005). TCD and ADC_mean (ρ = -0.61, p = 0.005) and TCD and ADC_{10th percentile} (ρ = -0.56, p = 0.01) were negatively correlated. No correlation was observed between percentage of Gleason pattern and ADC values.

Conclusion: DWI MRI can characterize focal prostate cancer using ADC_ratio, ADC_{10th percentile}, and ADC_mean, which correlate with pathological tumor cell density.