IMAGING

doi: 10.1590/S1677-55382011000200019

Is apparent diffusion coefficient associated with clinical risk scores for prostate cancers that are visible on 3-T MR images?
Turkbey B, Shah VP, Pang Y, Bernardo M, Xu S, Kruecker J, Locklin J, Baccala AA Jr, Rastinehad AR, Merino MJ, Shih JH, Wood BJ, Pinto PA, Choyke PL
Molecular Imaging Program, Center for Interventional Oncology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
Radiology. 2011; 258: 488-95

• Purpose: To investigate whether apparent diffusion coefficients (ADCs) derived from diffusion-weighted (DW) magnetic resonance (MR) imaging at 3 T correlate with the clinical risk of prostate cancer in patients with tumors that are visible on MR images, with MR imaging/transrectal ultrasonography (US) fusion-guided biopsy as a reference.
  Materials and Methods: Forty-eight consecutive patients (median age, 60 years; median serum prostate-specific antigen value, 6.3 ng/mL) who underwent DW imaging during 3-T MR imaging with an endorectal coil were included in this retrospective institutional review board-approved study, and informed consent was obtained from each patient. Patients underwent targeted MR imaging/transrectal US fusion-guided prostate biopsy. Mean ADCs of cancerous target tumors were correlated with Gleason and D’Amico clinical risk scores. The true risk group rate and predictive value of the mean ADC for classifying a tumor by its D’Amico clinical risk score was determined by using linear discriminant and receiver operating characteristic analyses.
  Results: A significant negative correlation was found between mean ADCs of tumors in the peripheral zone and their Gleason scores (P = 0.003; Spearman ? = -0.60) and D’Amico clinical risk scores (P < 0.0001; Spearman ? = -0.69). ADC was found to distinguish tumors in the peripheral zone with intermediate to high clinical risk from those with low clinical risk with a correct classification rate of 0.73.
  Conclusion: There is a significant negative correlation between ADCs and Gleason and D’Amico clinical risk scores. ADCs may therefore be useful in predicting the aggressiveness of prostate cancer. Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100667/-/DC1

• Editorial Comment
  The authors showed that endorectal 3T diffusion-weighted MR imaging (D-WMRI) and the calculated apparent diffusion coefficient (ADC), can be useful in the assessment of the aggressiveness of the peripheral zone prostate cancer lesions that are visible on conventional T2-weighted images. A significant negative correlation was found between mean apparent diffusion coefficients (ADCs) of prostate cancers in the peripheral zone and their Gleason score and D’Amico clinical risk score. As we know, D-WMRI is dependent on Brownian motion of water in biologic tissues. Since prostate cancerous tissues have higher cellularity and fibrosis than the non-cancerous tissue, restriction on Brownian motion of water tissue occurs and can be quantified by measurements the ADCs values. In this manuscript it was found that the mean ADC of tumors had a significant negative correlation with tumor Gleason scores and that a significant difference was also observed between mean ADCs values of low, intermediate, and high clinical risk tumors. Thus, ADCs values obtained from D-WMRI at endorectal 3 T were significantly lower in prostate cancers with intermediate and high clinical risk scores and higher Gleason scores. According to their results, ADC maps can be used to assess the aggressiveness of a prostate cancer lesion, potentially as an adjunct to information from other clinical sources (Gleason score, PSA, lesion size, lesion stage) to help select candidates for active surveillance and to follow these patients eventually replacing biopsies.
  This study has some limitations. First, they evaluated the role of D-WMRI only in patients presenting cancer of the peripheral zone. Patients with cancer in the transition zone were not included. Second, the authors used a home made system to quantify ADCs values of prostate cancer, thus comparison with similar studies that uses commercially available ADCs measurement system is not possible. Third, they compared only findings observed on conventional T2-weighted image and DWI. It has been shown that prostate cancer assessment by MRI is better accomplished with the combination of results of multiparametric studies (conventional T2-weighted images, spectroscopy, diffusion-weighted images and contrast perfusion studies).

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