Prediction of Locally Recurrent Prostate Cancer after Radiation Therapy: Incremental Value of 3T Diffusion-Weighted MRI

Purpose: To prospectively evaluate the incremental value of diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps in addition to T2-weighted imaging (T2WI) for predicting locally recurrent prostate cancer in patients with biochemical failure after radiation therapy. Materials and Methods: Thirty-six consecutive patients with an increased prostate-specific antigen level after radiation therapy underwent 3T MRI followed by transrectal biopsy. The MRI findings and biopsy results were correlated in sextant prostate sectors of peripheral zones (PZs). Two radiologists in consensus reviewed T2WI and combined T2WI and DWI with ADC maps, and rated the likelihood of recurrent cancer on a five-point scale. ADC values were calculated for recurrent cancer and benign tissue. Results: Of 216 sectors, 65 prostate sectors (30%) were positive for cancer in 18 patients. For predicting recurrent cancer, combined T2WI and DWI showed a greater sensitivity compared to T2WI (P < 0.001). A significantly greater area under the receiver operating characteristics curve (Az) was determined for combined T2WI and DWI (Az = 0.879, P < 0.01) as compared to T2WI (Az = 0.612). Mean ADC values between recurrent cancer and benign tissue showed a statistically significant difference (P < 0.01). Conclusion: For predicting locally recurrent prostate cancer after radiation therapy, the use of combined T2WI and DWI showed a better diagnostic performance compared to T2WI.