title: The use of positron emission tomography/computed tomography imaging in radiation therapy: a phantom study for setting internal target volume of biological target volume.
abstract: BACKGROUND
  Fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) is an important method for detecting tumours, planning radiotherapy treatment, and evaluating treatment responses. However, using the standardized uptake value (SUV) threshold with PET imaging may be suitable not to determine gross tumour volume but to determine biological target volume (BTV). The aim of this study was to extract internal target volume of BTV from PET images.
  
  
  METHODS
  Three spherical densities of (18)F-FDG were employed in a phantom with an air or water background with repetitive motion amplitudes of 0-30 mm. The PET data were reconstructed with attenuation correction (AC) based on CT images obtained by slow CT scanning (SCS) or helical CT scanning (HCS). The errors in measured SUVmax and volumes calculated using SUV threshold values based on SUVmax (THmax) in experiments performed with varying extents of respiratory motion and AC were analysed.
  
  
  RESULTS
  A partial volume effect (PVE) was not observed in spheres with diameters of ≥ 28 mm. When calculating SUVmax and THmax, using SCS for AC yielded smaller variance than using HCS (p<0.05). For spheres of 37- and 28-mm diameters in the phantom with either an air or water background, significant differences were observed when mean THmax of 30-, 20-, or 10-mm amplitude were compared with the stationary conditions (p<0.05). The average THmax values for 37-mm and 28-mm spheres with an air background were 0.362 and 0.352 in non-motion, respectively, and the mean THmax values for 37-mm and 28-mm spheres with a water background were 0.404 and 0.387 in non-motion and 0.244 and 0.263 in motion, respectively. When the phantom background was air, regardless of sphere concentration or size, THmax was dependent only on motion amplitude.
  
  
  CONCLUSIONS
  We found that there was no PVE for spheres with ≥ 28-mm diameters, and differences between SUVmax and THmax were reduced by using SCS for AC. In the head-and-neck and the abdomen, the standard values of THmax were 0.25 and 0.40 with and without respiratory movement, respectively. In the lungs, the value of THmax became the approximate expression depending on motion amplitude.
authors.affiliation: Department of Radiological Technology, Public Central Hospital of Matto Ishikawa, 3-8, Kuramitsu, Hakusan City, Ishikawa Pref, 924-8588, Japan. rt01@mattohp.com.|Department of Quantum Medical Technology, Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Ishikawa, Japan. rt01@mattohp.com.
authors.forename: Wataru
authors.initials: W
authors.lastname: Kawakami
authors.affiliation: Department of Quantum Medical Technology, Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Ishikawa, Japan. at@mhs.mp.kanazawa-u.ac.jp.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takemura
authors.affiliation: PET Imaging Center, Public Central Hospital of Matto Ishikawa, Ishikawa, Japan. yokoyama@mattohp.com.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Yokoyama
authors.affiliation: Department of Nuclear Medicine, Kanazawa University Hospital, Ishikawa, Japan. nakajima@med.kanazawa-u.ac.jp.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Nakajima
authors.affiliation: Department of Radiological Technology, Public Central Hospital of Matto Ishikawa, 3-8, Kuramitsu, Hakusan City, Ishikawa Pref, 924-8588, Japan. yoko_4401s@ybb.ne.jp.
authors.forename: Syoichi
authors.initials: S
authors.lastname: Yokoyama
authors.affiliation: Department of Quantum Medical Technology, Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Ishikawa, Japan. kk4217@staff.kanazawa-u.ac.jp.
authors.forename: Kichiro
authors.initials: K
authors.lastname: Koshida
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D009333:Neck / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D014018:Tissue Distribution; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18