title: Defining target volumes for stereotactic ablative radiotherapy of early-stage lung tumours: a comparison of three-dimensional 18F-fluorodeoxyglucose positron emission tomography and four-dimensional computed tomography.
abstract: OBJECTIVE
  High local control rates are achieved in stage I lung cancer using stereotactic ablative radiotherapy. Target delineation is commonly based on four-dimensional computed tomography (CT) scans. Target volumes defined by positron emission tomography/computed tomography (PET/CT) are compared with those defined by four-dimensional CT and conventional ('three-dimensional') (18)F-fluorodeoxyglucose ((18)F-FDG) PET/CT.
  
  
  METHODS
  For 16 stage I non-small cell lung cancer tumours, six approaches for deriving PET target volumes were evaluated: manual contouring, standardised uptake value (SUV) absolute threshold of 2.5, 35% of maximum SUV (35%SUV(MAX)), 41% of SUV(MAX) (41%SUV(MAX)) and two different source to background ratio techniques (SBR-1 and SBR-2). PET-derived target volumes were compared with the internal target volume (ITV) from the modified maximum intensity projection (MIP(MOD) ITV). Volumetric and positional correlation was assessed using the Dice similarity coefficient (DSC).
  
  
  RESULTS
  PET-based target volumes did not correspond to four-dimensional CT-based target volumes. The mean DSC relative to MIP(MOD) ITV were: PET manual = 0.64, SUV2.5 = 0.64, 35%SUV(MAX) = 0.63, 41%SUV(MAX) = 0.57. SBR-1 = 0.52, SBR-2 = 0.49. PET-based target volumes were smaller than corresponding MIP ITVs.
  
  
  CONCLUSIONS
  Conventional three-dimensional (18)F-FDG PET-derived target volumes for lung stereotactic ablative radiotherapy did not correspond well with those derived from four-dimensional CT, including those in routine clinical use (MIP(MOD) ITV). Caution is required in using three-dimensional PET for motion encompassing target volume delineation.
authors.affiliation: Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands. Gerry.Hanna@belfasttrust.hscni.net
authors.forename: G G
authors.initials: GG
authors.lastname: Hanna
authors.forename: J R
authors.initials: JR
authors.lastname: van Sörnsen de Koste
authors.forename: M R
authors.initials: MR
authors.lastname: Dahele
authors.forename: K J
authors.initials: KJ
authors.lastname: Carson
authors.forename: C J A
authors.initials: CJ
authors.lastname: Haasbeek
authors.forename: R
authors.initials: R
authors.lastname: Migchielsen
authors.forename: A R
authors.initials: AR
authors.lastname: Hounsell
authors.forename: S
authors.initials: S
authors.lastname: Senan
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery*; D019788:Fluorodeoxyglucose F18; D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery*; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography / Q000379:methods; D016634:Radiosurgery / Q000379:methods*
chemical_list: D019788:Fluorodeoxyglucose F18