Diffusion-weighted MRI of peripheral zone prostate cancer: comparison of tumor apparent diffusion coefficient with Gleason score and percentage of tumor on core biopsy.

OBJECTIVE: The objective of our study was to determine the relationship between the apparent diffusion coefficient (ADC) value on diffusion-weighted imaging (DWI) and Gleason score of prostate cancer and percentage of tumor involvement on prostate core biopsy. MATERIALS AND METHODS: We performed a retrospective study of 57 patients with biopsy-proven prostate cancer who underwent endorectal MRI with DWI between July 2007 and March 2008. Regions of interest (ROIs) were drawn on ADC maps at sites of visible tumor on DW images and ADC maps. A hierarchic mixed linear model was used to compare the ADC value of prostate cancer with the Gleason score and the percentage of tumor on core biopsy. RESULTS: Eighty-one sites of biopsy-proven prostate cancer were visible on DW images and ADC maps. The least-squares mean ADC for disease with a Gleason score of 6 was 0.860 x 10(-3) mm(2)/s (standard error of the mean [SEM], 0.036); Gleason score of 7, 0.702 x 10(-3) mm(2)/s (SEM, 0.030); Gleason score of 8, 0.672 x 10(-3) mm(2)/s (SEM, 0.057); and Gleason score of 9, 0.686 x 10(-3) mm(2)/s (SEM, 0.067). Differences between the mean ADC values for a prostate tumor with a Gleason score of 6 and one with a Gleason score of 7 (p = 0.0096) and for a prostate tumor with a Gleason score of 6 and one with a Gleason score of 8 (p = 0.0460) were significant. Comparison between the ADC and percentage of tumor on core biopsy showed a mean ADC decrease of 0.006 (range, 0.004-0.008 x 10(-3) mm(2)/s) for every 1% increase in tumor in the core biopsy specimen. CONCLUSION: DWI may help differentiate between low-risk (Gleason score, 6) and intermediate-risk (Gleason score, 7) prostate cancer and between low-risk (Gleason score, 6) and high-risk (Gleason score > 7) prostate cancer. There is an inverse relationship between the ADC and the percentage of tumor involvement on prostate core biopsies.