IMAGING

doi: 10.1590/S1677-55382010000400018

Diffusion-weighted MRI of peripheral zone prostate cancer: comparison of tumor apparent diffusion coefficient with Gleason score and percentage of tumor on core biopsy
Woodfield CA, Tung GA, Grand DJ, Pezzullo JA, Machan JT, Renzulli JF 2nd
Department of Diagnostic Imaging, Rhode Island Hospital, Providence, RI, USA
AJR Am J Roentgenol. 2010; 194: W316-22.

• 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.

• Editorial Comment
  In prostate cancer occurs significant reduction in the diffusion properties of water protons thus resulting in a reduction in the measured apparent diffusion coefficient (ADC) value relative to normal prostatic tissue. Several reports have been showing the utility of this technique. The combination of anatomic information obtained with conventional T2-weighted image with functional information, obtained with diffusion-weighted image, offers significant advantage over the use of either one of these techniques separately. This association significantly improves cancer detection and the accuracy in predicting the volume of cancer of the peripheral zone. This combined technique however is more effective in tumors larger than 0.5 cm3.
  In this publication the authors show that the ADC values of prostate cancer may help differentiate between low-risk (Gleason, 6) and intermediate-risk (Gleason score 7 disease and between low-risk and high-risk (Gleason> 7). The ADC values in this study were compared with results of prostate biopsy. In other words, higher cellular density found in poorly differentiated tumors is responsible for more restricted movement of water protons and thus will present lower mean ADC values. They also showed that lower ADC values are associated with a higher percentage of cancer on core biopsy and higher Gleason score. They predicted that this feature could be useful to further direct patient treatment.
  We have to remember however that the reported sensitivity and specificity of DWI with ADC maps for detecting prostate cancer on MRI performed at 1.5 T, range from 54% to 94% and from 61% to 100%, respectively. In this study, the authors had a relatively poor detection rate, since 56% of biopsy-proven sites of prostate cancer were not visible on DWI. Sites containing tumor and visible on DWI had higher percentage of tumor on core biopsy (mean 52%) than those not visible (mean 19%) and higher Gleason score.
  The results of this work further support our opinion that the best way to detect prostatic cancer by imaging is using a multiparametric MRI examination, which combines T2-weighted images, spectroscopy, diffusion-weighted image and dynamic contrast enhanced technique. Since each one of these techniques has inherent advantages and disadvantages, efforts have been made in order to determine which combination will present higher accuracy.

Dr. Adilson Prando
Head, Department of Radiology and
Diagnostic Imaging, Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: adilson.prando@gmail.com