title: Diffusion-weighted MRI for locally recurrent prostate cancer after external beam radiotherapy.
abstract: OBJECTIVE
  The objectives of our study were to establish the apparent diffusion coefficients (ADCs) of tumor and nontumor irradiated tissues in patients with suspected postradiation recurrence of prostate cancer and to determine the sensitivity and specificity of a combination of T2-weighted and diffusion-weighted imaging (DWI) for detecting local recurrence.
  
  
  METHODS
  Twenty-four patients with rising prostate-specific antigen levels after having completed radiation therapy 30-130 months earlier (median, 62 months) underwent endorectal T2-weighted imaging and DWI (b = 0, 100, 300, 500, and 800 s/mm(2)) followed by transrectal ultrasound (TRUS)-guided biopsy. Images were scored prospectively as positive for tumor if a region of low signal intensity on T2-weighted imaging within the prostate corresponded with a focally restricted area on the ADC map. A region of interest (ROI) was drawn around the suspicious lesion on a single slice of the ADC map and a corresponding ROI was drawn around presumed nontumor irradiated peripheral zone and central gland tissues on the opposite side of the prostate. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined against TRUS-guided biopsy reference standard (octant, n = 17; sextant, n = 5; two samples, n = 1; 12 samples, n = 1).
  
  
  RESULTS
  Sixteen of 24 patients (66.7%) had positive histology findings. The median tumor ROI area was 0.37 cm(2) (quartiles, 0.30 and 0.82 cm(2)). The sensitivity, specificity, PPV, and NPV for detecting tumor were 93.8%, 75%, 88.2%, and 85.7%, respectively. A cutoff ADC of 1216 × 10(-6) mm(2)/s could predict tumor with 100% sensitivity and 96% specificity (area under the receiver operating characteristic curve = 0.992).
  
  
  CONCLUSIONS
  An ADC derived from DWI is a useful adjunct to T2-weighted MRI for detecting local tumor recurrence larger than 0.4 cm(2) within the prostate.
authors.affiliation: Cancer Research UK Clinical Magnetic Resonance Research Group, Institute of Cancer Research and Royal Marsden Hospital, Sutton, Surrey, United Kingdom.
authors.forename: Veronica A
authors.initials: VA
authors.lastname: Morgan
authors.forename: Sophie F
authors.initials: SF
authors.lastname: Riches
authors.forename: Sharon
authors.initials: S
authors.lastname: Giles
authors.forename: David
authors.initials: D
authors.lastname: Dearnaley
authors.forename: Nandita M
authors.initials: NM
authors.lastname: deSouza
mesh_terms: D000368:Aged; D001706:Biopsy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000473:pathology*; D011237:Predictive Value of Tests; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D018084:Ultrasonography, Interventional