title: Interobserver variation in parotid gland delineation: a study of its impact on intensity-modulated radiotherapy solutions with a systematic review of the literature.
abstract: OBJECTIVE
  This study evaluates the interobserver variation in parotid gland delineation and its impact on intensity-modulated radiotherapy (IMRT) solutions.
  
  
  METHODS
  The CT volumetric data sets of 10 patients with oropharyngeal squamous cell carcinoma who had been treated with parotid-sparing IMRT were used. Four radiation oncologists and three radiologists delineated the parotid gland that had been spared using IMRT. The dose-volume histogram (DVH) for each study contour was calculated using the IMRT plan actually delivered for that patient. This was compared with the original DVH obtained when the plan was used clinically.
  
  
  RESULTS
  70 study contours were analysed. The mean parotid dose achieved during the actual treatment was within 10% of 24 Gy for all cases. Using the study contours, the mean parotid dose obtained was within 10% of 24 Gy for only 53% of volumes by radiation oncologists and 55% of volumes by radiologists. The parotid DVHs of 46% of the study contours were sufficiently different from those used clinically, such that a different IMRT plan would have been produced.
  
  
  CONCLUSIONS
  Interobserver variation in parotid gland delineation is significant. Further studies are required to determine ways of improving the interobserver consistency in parotid gland definition.
authors: Department of Clinical Oncology, Norfolk and Norwich University Hospital, Norwich, UK. suatloo@doctors.org.uk
authors: S W
authors: SW
authors: Loo
authors: W M C
authors: WM
authors: Martin
authors: P
authors: P
authors: Smith
authors: S
authors: S
authors: Cherian
authors: T W
authors: TW
authors: Roques
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D006801:Humans; D015588:Observer Variation; D009929:Organ Size; D059351:Organ Sparing Treatments; D009959:Oropharyngeal Neoplasms / Q000532:radiotherapy*; D010306:Parotid Gland / Q000000981:diagnostic imaging* / Q000528:radiation effects; D011829:Radiation Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*