title: 3D Variation in delineation of head and neck organs at risk.
abstract: BACKGROUND
  Consistent delineation of patient anatomy becomes increasingly important with the growing use of highly conformal and adaptive radiotherapy techniques. This study investigates the magnitude and 3D localization of interobserver variability of organs at risk (OARs) in the head and neck area with application of delineation guidelines, to establish measures to reduce current redundant variability in delineation practice.
  
  
  METHODS
  Interobserver variability among five experienced radiation oncologists was studied in a set of 12 head and neck patient CT scans for the spinal cord, parotid and submandibular glands, thyroid cartilage, and glottic larynx. For all OARs, three endpoints were calculated: the Intraclass Correlation Coefficient (ICC), the Concordance Index (CI) and a 3D measure of variation (3D SD).
  
  
  RESULTS
  All endpoints showed largest interobserver variability for the glottic larynx (ICC = 0.27, mean CI = 0.37 and 3D SD = 3.9 mm). Better agreement in delineations was observed for the other OARs (range, ICC = 0.32-0.83, mean CI = 0.64-0.71 and 3D SD = 0.9-2.6 mm). Cranial, caudal, and medial regions of the OARs showed largest variations. All endpoints provided support for improvement of delineation practice.
  
  
  CONCLUSIONS
  Variation in delineation is traced to several regional causes. Measures to reduce this variation can be: (1) guideline development, (2) joint delineation review sessions and (3) application of multimodality imaging. Improvement of delineation practice is needed to standardize patient treatments.
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands. c.l.brouwer@umcg.nl
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Brouwer
authors.forename: Roel J H M
authors.initials: RJ
authors.lastname: Steenbakkers
authors.forename: Edwin
authors.initials: E
authors.lastname: van den Heuvel
authors.forename: Joop C
authors.initials: JC
authors.lastname: Duppen
authors.forename: Arash
authors.initials: A
authors.lastname: Navran
authors.forename: Henk P
authors.initials: HP
authors.lastname: Bijl
authors.forename: Olga
authors.initials: O
authors.lastname: Chouvalova
authors.forename: Fred R
authors.initials: FR
authors.lastname: Burlage
authors.forename: Harm
authors.initials: H
authors.lastname: Meertens
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Langendijk
authors.forename: Aart A
authors.initials: AA
authors.lastname: van 't Veld
mesh_terms: D006258:Head and Neck Neoplasms / Q000453:epidemiology* / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional; D015588:Observer Variation; D058958:Organs at Risk / Q000000981:diagnostic imaging*; D018787:Radiation Oncology / Q000592:standards*; D014057:Tomography, X-Ray Computed