title: Prostate contouring uncertainty in megavoltage computed tomography images acquired with a helical tomotherapy unit during image-guided radiation therapy.
abstract: OBJECTIVE
  To evaluate the image-guidance capabilities of megavoltage computed tomography (MVCT), this article compares the interobserver and intraobserver contouring uncertainty in kilovoltage computed tomography (KVCT) used for radiotherapy planning with MVCT acquired with helical tomotherapy.
  
  
  METHODS
  Five prostate-cancer patients were evaluated. Each patient underwent a KVCT and an MVCT study, a total of 10 CT studies. For interobserver variability analysis, four radiation oncologists, one physicist, and two radiation therapists (seven observers in total) contoured the prostate and seminal vesicles (SV) in the 10 studies. The intraobserver variability was assessed by asking all observers to repeat the contouring of 1 patient's KVCT and MVCT studies. Quantitative analysis of contour variations was performed by use of volumes and radial distances.
  
  
  RESULTS
  The interobserver and intraobserver contouring uncertainty was larger in MVCT compared with KVCT. Observers consistently segmented larger volumes on MVCT where the ratio of average prostate and SV volumes was 1.1 and 1.2, respectively. On average (interobserver and intraobserver), the local delineation variability, in terms of standard deviations [Deltasigma = radical(sigma2MVCT-sigma2KVCT)], increased by 0.32 cm from KVCT to MVCT.
  
  
  CONCLUSIONS
  Although MVCT was inferior to KVCT for prostate delineation, the application of MVCT in prostate radiotherapy remains useful.
authors.affiliation: Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.
authors.forename: William Y
authors.initials: WY
authors.lastname: Song
authors.forename: Bernard
authors.initials: B
authors.lastname: Chiu
authors.forename: Glenn S
authors.initials: GS
authors.lastname: Bauman
authors.forename: Michael
authors.initials: M
authors.lastname: Lock
authors.forename: George
authors.initials: G
authors.lastname: Rodrigues
authors.forename: Robert
authors.initials: R
authors.lastname: Ash
authors.forename: Craig
authors.initials: C
authors.lastname: Lewis
authors.forename: Aaron
authors.initials: A
authors.lastname: Fenster
authors.forename: Jerry J
authors.initials: JJ
authors.lastname: Battista
authors.forename: Jake
authors.initials: J
authors.lastname: Van Dyk
mesh_terms: D006801:Humans; D008297:Male; D015588:Observer Variation; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D015642:Radiology, Interventional; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012669:Seminal Vesicles / Q000000981:diagnostic imaging*; D036542:Tomography, Spiral Computed; D035501:Uncertainty