title: Validation of a 4D-PET maximum intensity projection for delineation of an internal target volume.
abstract: OBJECTIVE
  The delineation of internal target volumes (ITVs) in radiation therapy of lung tumors is currently performed by use of either free-breathing (FB) (18)F-fluorodeoxyglucose-positron emission tomography-computed tomography (FDG-PET/CT) or 4-dimensional (4D)-CT maximum intensity projection (MIP). In this report we validate the use of 4D-PET-MIP for the delineation of target volumes in both a phantom and in patients.
  
  
  METHODS
  A phantom with 3 hollow spheres was prepared surrounded by air then water. The spheres and water background were filled with a mixture of (18)F and radiographic contrast medium. A 4D-PET/CT scan was performed of the phantom while moving in 4 different breathing patterns using a programmable motion device. Nine patients with an FDG-avid lung tumor who underwent FB and 4D-PET/CT and >5 mm of tumor motion were included for analysis. The 3 spheres and patient lesions were contoured by 2 contouring methods (40% of maximum and PET edge) on the FB-PET, FB-CT, 4D-PET, 4D-PET-MIP, and 4D-CT-MIP. The concordance between the different contoured volumes was calculated using a Dice coefficient (DC). The difference in lung tumor volumes between FB-PET and 4D-PET volumes was also measured.
  
  
  RESULTS
  The average DC in the phantom using 40% and PET edge, respectively, was lowest for FB-PET/CT (DCAir = 0.72/0.67, DCBackground 0.63/0.62) and highest for 4D-PET/CT-MIP (DCAir = 0.84/0.83, DCBackground = 0.78/0.73). The average DC in the 9 patients using 40% and PET edge, respectively, was also lowest for FB-PET/CT (DC = 0.45/0.44) and highest for 4D-PET/CT-MIP (DC = 0.72/0.73). In the 9 lesions, the target volumes of the FB-PET using 40% and PET edge, respectively, were on average 40% and 45% smaller than the 4D-PET-MIP.
  
  
  CONCLUSIONS
  A 4D-PET-MIP produces volumes with the highest concordance with 4D-CT-MIP across multiple breathing patterns and lesion sizes in both a phantom and among patients. Freebreathing PET/CT consistently underestimates ITV when compared with 4D PET/CT for a lesion affected by respiration.
authors.affiliation: Centre for Molecular Imaging, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia. jason.callahan@petermac.org
authors.forename: Jason
authors.initials: J
authors.lastname: Callahan
authors.forename: Tomas
authors.initials: T
authors.lastname: Kron
authors.forename: Michal
authors.initials: M
authors.lastname: Schneider-Kolsky
authors.forename: Leon
authors.initials: L
authors.lastname: Dunn
authors.forename: Mick
authors.initials: M
authors.lastname: Thompson
authors.forename: Shankar
authors.initials: S
authors.lastname: Siva
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Aarons
authors.forename: David
authors.initials: D
authors.lastname: Binns
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Hicks
mesh_terms: D003287:Contrast Media; D019788:Fluorodeoxyglucose F18; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D009068:Movement; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D012119:Respiration
chemical_list: D003287:Contrast Media; D019788:Fluorodeoxyglucose F18