title: Clinical evaluation of soft tissue organ boundary visualization on cone-beam computed tomographic imaging.
abstract: OBJECTIVE
  Cone-beam computed tomographic images (CBCTs) are increasingly used for setup correction, soft tissue targeting, and image-guided adaptive radiotherapy. However, CBCT image quality is limited by low contrast and imaging artifacts. This analysis investigates the detectability of soft tissue boundaries in CBCT by performing a multiple-observer segmentation study.
  
  
  METHODS
  In four prostate cancer patients prostate, bladder and rectum were repeatedly delineated by five observers on CBCTs and fan-beam CTs (FBCTs). A volumetric analysis of contouring variations was performed by calculating coefficients of variation (COV: standard deviation/average volume). The topographical distribution of contouring variations was analyzed using an average surface mesh-based method.
  
  
  RESULTS
  Observer- and patient-averaged COVs for FBCT/CBCT were 0.09/0.19 for prostate, 0.05/0.08 for bladder, and 0.09/0.08 for rectum. Contouring variations on FBCT were significantly smaller than on CBCT for prostate (p < 0.03) and bladder (p < 0.04), but not for rectum (p < 0.37; intermodality differences). Intraobserver variations from repeated contouring of the same image set were not significant for either FBCT or CBCT (p < 0.05). Average standard deviations of individual observers' contour differences from average surface meshes on FBCT vs. CBCT were 1.5 vs. 2.1 mm for prostate, 0.7 vs. 1.4 mm for bladder, and 1.3 vs. 1.5 mm for rectum. The topographical distribution of contouring variations was similar for FBCT and CBCT.
  
  
  CONCLUSIONS
  Contouring variations were larger on CBCT than FBCT, except for rectum. Given the well-documented uncertainty in soft tissue contouring in the pelvis, improvement of CBCT image quality and establishment of well-defined soft tissue identification rules are desirable for image-guided radiotherapy.
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA. eweiss@mcvh-vcu.edu
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Weiss
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.forename: William
authors.initials: W
authors.lastname: Sleeman
authors.forename: Joshua
authors.initials: J
authors.lastname: Bryant
authors.forename: Priya
authors.initials: P
authors.lastname: Mitra
authors.forename: Michael
authors.initials: M
authors.lastname: Myers
authors.forename: Tatjana
authors.initials: T
authors.lastname: Ivanova
authors.forename: Nitai
authors.initials: N
authors.lastname: Mukhopadhyay
authors.forename: Viswanathan
authors.initials: V
authors.lastname: Ramakrishnan
authors.forename: Martin
authors.initials: M
authors.lastname: Murphy
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Williamson
mesh_terms: D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000592:standards; D006801:Humans; D008297:Male; D015588:Observer Variation; D009929:Organ Size; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging*; D012007:Rectum / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000592:standards; D001743:Urinary Bladder / Q000000981:diagnostic imaging*