title: Assessment of response to radiotherapy for prostate cancer: value of diffusion-weighted MRI at 3 T.
abstract: 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 3 T using a phased-array coil.
  
  
  METHODS
  Forty-nine patients with biopsy-proven prostate cancer who received radiotherapy underwent diffusion-weighted imaging (DWI) at 3 T and were included in the study. Biopsies in all patients were performed before the initial MRI examination (range, 15-35 days before MRI; mean, 23.4 days). All 49 patients underwent DWI (b values = 0 and 1,000 s/mm(2)) before and 1-5 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
  A total of 57 cancers (peripheral zone, n = 45; transition zone, n = 12) were found in 46 patients. For the tumors, the mean ADC value after therapy (1.61 x 10(-3) mm(2)/s) was increased compared with the mean ADC value before therapy (1.0 x 10(-3) mm(2)/s) (p < 0.001). 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 > 0.1). The median PSA level after therapy (0.49 ng/mL) was decreased compared with the median PSA level before therapy (20.0 ng/mL).
  
  
  CONCLUSIONS
  With the use of a 3-T MR scanner, our preliminary results suggest that ADC values may be useful as an imaging biomarker for monitoring therapeutic response of prostate cancer to radiotherapy.
authors.affiliation: Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Kangnam-gu, Seoul 135-710, Republic of Korea.
authors.forename: Inyoung
authors.initials: I
authors.lastname: Song
authors.forename: Chan Kyo
authors.initials: CK
authors.lastname: Kim
authors.forename: Byung Kwan
authors.initials: BK
authors.lastname: Park
authors.forename: Won
authors.initials: W
authors.lastname: Park
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional
chemical_list: D017430:Prostate-Specific Antigen