title: The impact of gross tumor volume (GTV) and clinical target volume (CTV) definition on the total accuracy in radiotherapy theoretical aspects and practical experiences.
abstract: OBJECTIVE
  To evaluate the impact of interobserver variability in the contouring of gross tumor volumes (GTVs) and clinical target volumes (CTVs) on the global geometric accuracy in radiation therapy.
  
  
  METHODS
  In a review of the currently available literature, the magnitude of interobserver variability is analyzed, causes and consequences are discussed. Uncertainties due to inconsistencies in contouring are related to other sources of geometric errors, particularly patient positioning and organ motion.
  
  
  RESULTS
  Interobserver variability is a major -- for some tumor locations probably the largest -- factor contributing to geometric inaccuracy. Causes are multifactorial and include image- and observer-related factors, such as the subjective interpretation of image information.
  
  
  CONCLUSIONS
  Consequences to reduce interobserver variability are proposed, among others the selection of adequate imaging modalities, intensified radiologic training, and the use of telecommunication tools.
authors.affiliation: Department of Radiation Therapy, University of Göttingen, Germany. eweiss@gwdg.de
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Weiss
authors.forename: Clemens F
authors.initials: CF
authors.lastname: Hess
mesh_terms: D002983:Clinical Competence; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D009369:Neoplasms / Q000175:diagnosis / Q000473:pathology / Q000532:radiotherapy*; D015588:Observer Variation; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome