title: Normal tissue anatomy for oropharyngeal cancer: contouring variability and its impact on optimization.
abstract: OBJECTIVE
  To evaluate the variability of organ at risk (OAR) delineation and the resulting impact on intensity modulated radiation therapy (IMRT) treatment plan optimization in head-and-neck cancer.
  
  
  METHODS
  An expert panel of 3 radiation oncologists jointly delineated OARs, including the parotid and submandibular glands (SM), pharyngeal constrictors (PC), larynx, and glottis (GL), in 10 patients with advanced oropharynx cancer in 3 contouring sessions, spaced at least 1 week apart. Contour variability and uncertainty, as well as their dosimetric impact on IMRT planning for each case, were assessed.
  
  
  RESULTS
  The mean difference in total volume for each OAR was 1 cm(3) (σ 0.5 cm(3)). Mean fractional overlap was 0.7 (σ 0.1) and was highest (0.8) for the larynx and bilateral SMs and parotids and lowest (0.5) for PC. There were considerable spatial differences in contours, with the ipsilateral parotid and PC displaying the most variability (0.9 cm), which was most prominent in cases in which tumors obliterated fat planes. Both SMs and GL had the smallest differences (0.5 cm). The mean difference in OAR dose was 0.9 Gy (range 0.6-1.1 Gy, σ 0.1 Gy), with the smallest difference for GL and largest for both SMs and the larynx.
  
  
  CONCLUSIONS
  Despite substantial difference in OAR contours, optimization was barely affected, with a 0.9-Gy mean difference between optimizations, suggesting relative insensitivity of dose distributions for IMRT of oropharynx cancer to the extent of OARs.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109, USA. maryfeng@umich.edu
authors.forename: Mary
authors.initials: M
authors.lastname: Feng
authors.forename: Candan
authors.initials: C
authors.lastname: Demiroz
authors.forename: Karen A
authors.initials: KA
authors.lastname: Vineberg
authors.forename: Avraham
authors.initials: A
authors.lastname: Eisbruch
authors.forename: James M
authors.initials: JM
authors.lastname: Balter
mesh_terms: D032921:Consensus; D005931:Glottis / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D007830:Larynx / Q000000981:diagnostic imaging / Q000528:radiation effects; D009929:Organ Size; D058958:Organs at Risk / Q000000981:diagnostic imaging* / Q000528:radiation effects; D009959:Oropharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects; D010609:Pharyngeal Muscles / Q000000981:diagnostic imaging / Q000528:radiation effects; D011446:Prospective Studies; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D013363:Submandibular Gland / Q000000981:diagnostic imaging / Q000528:radiation effects