title: The effect of contouring variability on dosimetric parameters for brain metastases treated with stereotactic radiosurgery.
abstract: OBJECTIVE
  To quantify the effect of contouring variation on stereotactic radiosurgery plan quality metrics for brain metastases.
  
  
  METHODS
  Fourteen metastases, each contoured by 8 physicians, formed the basis of this study. A template-based dynamic conformal 5-arc dose distribution was developed for each of the 112 contours, and each dose distribution was applied to the 7 other contours in each patient set. Radiation Therapy Oncology Group (RTOG) plan quality metrics and the Paddick conformity index were calculated for each of the 896 combinations of dose distributions and contours.
  
  
  RESULTS
  The ratio of largest to smallest contour volume for each metastasis varied from 1.25 to 4.47, with a median value of 1.68 (n=8). The median absolute difference in RTOG conformity index between the value for the reference contour and the values for the alternative contours was 0.35. The variation of the range of conformity index for all contours for a given tumor varied with the tumor size.
  
  
  CONCLUSIONS
  The high degree of interobserver contouring variation strongly suggests that peer review or consultation should be adopted to standardize tumor volume prescription. Observer confidence was not reflected in contouring consistency. The impact of contouring variability on plan quality metrics, used as criteria for clinical trial protocol compliance, was such that the category of compliance was robust to interobserver effects only 70% of the time.
authors.affiliation: Department of Medical Physics, Tom Baker Cancer Center, Calgary, Alberta, Canada. Electronic address: Julia.Stanley@albertahealthservices.ca.
authors.forename: Julia
authors.initials: J
authors.lastname: Stanley
authors.forename: Peter
authors.initials: P
authors.lastname: Dunscombe
authors.forename: Harold
authors.initials: H
authors.lastname: Lau
authors.forename: Paul
authors.initials: P
authors.lastname: Burns
authors.forename: Gerald
authors.initials: G
authors.lastname: Lim
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Liu
authors.forename: Robert
authors.initials: R
authors.lastname: Nordal
authors.forename: Yves
authors.initials: Y
authors.lastname: Starreveld
authors.forename: Boris
authors.initials: B
authors.lastname: Valev
authors.forename: Jon-Paul
authors.initials: JP
authors.lastname: Voroney
authors.forename: David P
authors.initials: DP
authors.lastname: Spencer
mesh_terms: D000465:Algorithms; D000704:Analysis of Variance; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000556:secondary* / Q000601:surgery; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards; D064847:Multimodal Imaging / Q000379:methods / Q000592:standards*; D009462:Neurology / Q000592:standards; D009493:Neurosurgery / Q000523:psychology / Q000592:standards; D015588:Observer Variation; D018787:Radiation Oncology / Q000592:standards; D016634:Radiosurgery / Q000379:methods / Q000592:standards; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D012016:Reference Values; D020377:Self Efficacy; D014057:Tomography, X-Ray Computed / Q000592:standards; D047368:Tumor Burden