title: Retrospective attenuation correction of PET data for radiotherapy planning using a free breathing CT.
abstract: OBJECTIVE
  To evaluate the image quality of retrospectively attenuation corrected Positron Emission Tomography (PET) scans used for gross tumor volume (GTV) delineation in lung cancer patients.
  
  
  METHODS
  Data of 13 lymph node positive lung cancer patients were acquired on separate CT and PET scanners under free breathing conditions (for radiotherapy planning). First we determined a protocol for CT/PET registration. Second, we compared the image quality of attenuation-corrected PET images using positron transmission images and CT images, in terms of signal-to-noise ratio (SNR) and lesion-to-background ratio (contrast).
  
  
  RESULTS
  The largest differences between manual and automatic CT/PET registration were found in the anterior-posterior direction with a mean of 1.8 mm (SD 1.0 mm). Differences in rotations were always smaller than 1.0 degrees . The attenuation-corrected images using CT showed a larger SNR (mean 30%, SD 17%) and larger contrast (mean 14.0%, SD 8.5%) compared to attenuation-corrected images using positron transmission. For lymph nodes, the mean contrast was 16% (SD 6.4%) larger.
  
  
  CONCLUSIONS
  This study demonstrated that attenuation correction based on CT provides a better image quality for GTV delineation than when using positron transmission for attenuation correction. Retrospective attenuation correction of PET scans based on registered CT is a good alternative for a dedicated PET/CT scanner if a free-breathing CT is available, e.g., for radiotherapy planning, and allows the use of CT with diagnostic quality for attenuation correction.
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: Lambert
authors.initials: L
authors.lastname: Zijp
authors.forename: Joop C
authors.initials: JC
authors.lastname: Duppen
authors.forename: Emile F I
authors.initials: EF
authors.lastname: Comans
authors.forename: Saar H
authors.initials: SH
authors.lastname: Muller
authors.forename: Peter J C M
authors.initials: PJ
authors.lastname: Nowak
authors.forename: Coen R N
authors.initials: CR
authors.lastname: Rasch
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D012119:Respiration; D014057:Tomography, X-Ray Computed