title: A comparison of AAPM TG-108 PET/CT shielding recommendations to measurements in an oncology center.
abstract: OBJECTIVE
  The AAPM Task Group Report 108 provides methods for calculating photon shielding for PET scanner suites. Calculated shielding requirements may be conservative in some areas when assuming a static point source and absence of scanner self-shielding. This study compares TG-108 shielding calculations to measured data from an oncology PET/CT scanner.
  
  
  METHODS
  Optically stimulated luminescence dosimeters were place at eight positions at 1 m height on the walls surrounding a PET/CT scanner. Dosimeters were also placed at three positions in the ceiling along the axial length of the scanner. Each position contained three dosimeters covered with 0, 1.6, or 3.2 mm of lead to separate the x-ray and 511 keV photon components. Dosimeters were switched out every month for a total collection period of 10 months. The dosimeter measurements were compared to TG-108 estimates by dividing the measured dose by the TG-108 calculated dose.
  
  
  RESULTS
  The PET gantry provided considerable shielding in the transaxial detector plane resulting in a low measured to calculated dose ratio of 0.26. The ratio increased to 0.48 at 45 degrees between the transaxial and axial planes then to 0.95 at the head of the scanner. Dose ratios at the foot of the scanner were near unity at the walls but as high as 2 in the ceiling. The high ceiling dose was attributed to unshielded radiation contributions from the dose handling area.
  
  
  CONCLUSIONS
  TG-108 provides accurate dose estimates when there is no barrier between the patient and measurement location. Careful consideration of the shielding properties of the scanner can reduce the amount of shielding necessary to include in walls.
authors.affiliation: Emory School of Medicine, Emory University, Atlanta, Georgia 30322, USA. jnye@emory.edu
authors.forename: Jonathon A
authors.initials: JA
authors.lastname: Nye
authors.forename: Michael
authors.initials: M
authors.lastname: Dubose
authors.forename: John R
authors.initials: JR
authors.lastname: Votaw
mesh_terms: D006801:Humans; D008495:Medical Oncology / Q000379:methods*; D017785:Photons; D049268:Positron-Emission Tomography / Q000379:methods*; D017410:Practice Guidelines as Topic; D011829:Radiation Dosage; D055618:Radiation Equipment and Supplies; D011835:Radiation Protection; D011874:Radiometry; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014965:X-Rays