title: Impact of anatomical location on value of CT-PET co-registration for delineation of lung tumors.
abstract: OBJECTIVE
  To derive guidelines for the need to use positron emission tomography (PET) for delineation of the primary tumor (PT) according to its anatomical location in the lung.
  
  
  METHODS
  In 22 patients with non-small-cell lung cancer, thoracic X-ray computed tomography (CT) and PET were performed. Eleven radiation oncologists delineated the PT on the CT and on the CT-PET registered scans. The PTs were classified into two groups. In Group I patients, the PT was surrounded by lung or visceral pleura, without venous invasion, without extension to chest wall or the mediastinum over more than one quarter of its surface. In Group II patients, the PT invaded the hilar region, heart, great vessels, pericardium, mediastinum over more than one quarter of its surface and/or associated with atelectasis. A comparison of interobserver variability for each group was performed and expressed as a local standard deviation.
  
  
  RESULTS
  The comparison of delineations showed a good reproducibility for Group I, with an average SD of 0.4 cm on CT and an average SD of 0.3 cm on CT-PET (p = 0.1628). There was also a significant improvement with CT-PET for Group II, with an average SD of 1.3 cm on CT and SD of 0.4 cm on CT-PET (p = 0.0003). The improvement was mainly located at the atelectasis/tumor interface. At the tumor/lung and tumor/hilum interfaces, the observer variation was similar with both modalities.
  
  
  CONCLUSIONS
  Using PET for PT delineation is mandatory to decrease interobserver variability in the hilar region, heart, great vessels, pericardium, mediastinum, and/or the region associated with atelectasis; however it is not essential for delineation of PT surrounded by lung or visceral pleura, without venous invasion or extension to the chest wall.
authors.affiliation: Georges Pompidou European Hospital, Paris, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Fitton
authors.forename: Roel J H M
authors.initials: RJ
authors.lastname: Steenbakkers
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gilhuijs
authors.forename: Joop C
authors.initials: JC
authors.lastname: Duppen
authors.forename: Peter J C M
authors.initials: PJ
authors.lastname: Nowak
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.forename: Coen R N
authors.initials: CR
authors.lastname: Rasch
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000379:methods*; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*