title: [Prostate and seminal vesicle displacement following urethrography: a computed tomography-based study].
abstract: OBJECTIVE
  It has been suggested that urethrography used for localization of the prostate apex may cause a systematic cranial displacement of the organ. Our objective was to use CT-CT image registration to identify if a clinically relevant systematic shift occurs in the position of the prostate and seminal vesicles following retrograde urethrography.
  
  
  METHODS
  Patients were scanned twice at the time of simulation. They were imaged supine, bladder empty. Scan resolution was 512x512 with 5 mm cuts. After the first CT sequence, with the patient still on the CT couch, an urethrogram was performed. The patients were then re-scanned. The image sets were registered through the use of external skin fiducials. A single author reviewed x, y and z-axis displacement. Z-axis motion of the prostate was also assessed by having three blinded radiation oncologists mark the cranial limit of the prostate on all 104 image sets.
  
  
  RESULTS
  Fifty-two pairs of CT scans were analyzed for post-urethrogram organ displacement. The mean x axis displacement of the prostate was 0.016 mm (P=0.8), the mean y-axis displacement was 1.3 mm anterior (P<0.001). Mean z-axis displacement of the prostate, using the blinded assessments, was a 1.35 mm cranial shift (P<0.0001). Analogous shifts were identified for the seminal vesicles.
  
  
  CONCLUSIONS
  Our results suggest a small cranial and anterior displacement of the prostate and seminal vesicles following retrograde urethrography.
authors: Département d'oncologie, division de radiothérapie, université McGill, Montréal, Québec, Canada. david.roberge@muhc.mcgill.ca
authors: D
authors: D
authors: Roberge
authors: R
authors: R
authors: Corns
authors: L
authors: L
authors: Souhami
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009068:Movement; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging*; D011859:Radiography / Q000009:adverse effects; D015203:Reproducibility of Results; D012669:Seminal Vesicles / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014521:Urethra / Q000000981:diagnostic imaging* / Q000502:physiology