title: Prostate volume contouring: a 3D analysis of segmentation using 3DTRUS, CT, and MR.
abstract: OBJECTIVE
  This study evaluated the reproducibility and modality differences of prostate contouring after brachytherapy implant using three-dimensional (3D) transrectal ultrasound (3DTRUS), T2-weighted magnetic resonance (MR), and computed tomography (CT) imaging.
  
  
  METHODS
  Seven blinded observers contoured 10 patients' prostates, 30 day postimplant, on 3DTRUS, MR, and CT images to assess interobserver variability. Randomized images were contoured twice by each observer. We analyzed length and volume measurements and performed a 3D analysis of intra- and intermodality variation.
  
  
  RESULTS
  Average volume ratios were 1.16 for CT/MR, 0.90 for 3DTRUS/MR, and 1.30 for CT/3DTRUS. Overall contouring variability was largest for CT and similar for MR and 3DTRUS. The greatest variability of CT contours occurred at the posterior and anterior portions of the midgland. On MR, overall variability was smaller, with a maximum in the anterior region. On 3DTRUS, high variability occurred in anterior regions of the apex and base, whereas the prostate-rectum interface had the smallest variability. The shape of the prostate on MR was rounder, with the base and apex of similar size, whereas CT contours had broad, flat bases narrowing toward the apex. The average percent of surface area that was significantly different (95% confidence interval) for CT/MR was 4.1%; 3DTRUS/MR, 10.7%; and CT/3DTRUS, 6.3%. The larger variability of CT measurements made significant differences more difficult to detect.
  
  
  CONCLUSIONS
  The contouring of prostates on CT, MR, and 3DTRUS results in systematic differences in the locations of and variability in prostate boundary definition between modalities. MR and 3DTRUS display the smallest variability and the closest correspondence.
authors.affiliation: Department of Medical Physics, Tom Baker Cancer Centre, and Departments of Oncology and Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada. wendy.smith@cancerboard.ab.ca
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Smith
authors.forename: Craig
authors.initials: C
authors.lastname: Lewis
authors.forename: Glenn
authors.initials: G
authors.lastname: Bauman
authors.forename: George
authors.initials: G
authors.lastname: Rodrigues
authors.forename: David
authors.initials: D
authors.lastname: D'Souza
authors.forename: Robert
authors.initials: R
authors.lastname: Ash
authors.forename: Derek
authors.initials: D
authors.lastname: Ho
authors.forename: Varagur
authors.initials: V
authors.lastname: Venkatesan
authors.forename: Dónal
authors.initials: D
authors.lastname: Downey
authors.forename: Aaron
authors.initials: A
authors.lastname: Fenster
mesh_terms: D001918:Brachytherapy; D006801:Humans; D021621:Imaging, Three-Dimensional; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008297:Male; D015588:Observer Variation; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000648:ultrastructure; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes