The role of diffusion-weighted MRI: In assessment of response to radiotherapy for prostate cancer

Objective: The objective of our study was to investigate the changes of apparent diffusion coefficient (ADC) values in prostate cancers before and after radiotherapy at 1.5 T using a phased-array coil.Materials and methods: Twenty-five patients with biopsy-proven prostate cancer who received radiotherapy underwent diffusion-weighted imaging (DWI) at 1.5 T and were included in the study. Biopsies in all patients were performed before the initial MRI examination (range, 15–30 days before MRI; mean, 21.1 days). All 25 patients underwent DWI (b values = 0 and 1000 s/mm2) before and 1–3 months after the completion of radiotherapy. The changes in ADC values were measured for cancers and benign tissues before and after therapy. Additionally, the changes in serum prostate-specific antigen (PSA) levels were evaluated before and after therapy.Results: The mean ADC value after therapy (1.418 × 10−3 mm2/s) was increased compared with the mean ADC value before therapy (0.756 × 10−3 mm2/s) (p < 0.001) in cancer prostate. After radiotherapy, the mean ADC values of benign peripheral zones and of benign transition zones were statistically significantly decreased compared with those before radiotherapy (p < 0.05). Before treatment, a significant difference of ADC values between the tumors and benign tissues was found (p < 0.001), whereas there was no significant difference of ADC values between them after treatment (p > 0.5). The median PSA level after therapy (1.39 ng/mL) was decreased compared with the median PSA level before therapy (27.20 ng/mL).Conclusion: With the use of a 1.5-T MR scanner, our preliminary results suggest that ADC values may be useful as a non-invasive imaging biomarker for monitoring therapeutic response of prostate cancer to radiotherapy