title: Normalized CT dose index of the CT scanners used in the National Lung Screening Trial.
abstract: OBJECTIVE
  The National Lung Screening Trial includes 33 participating institutions that performed 75,133 lung cancer screening CT examinations for 26,724 subjects during 2002-2007. For trial quality assurance reasons, CT radiation dose measurement data were collected from all MDCT scanners used in the trial.
  
  
  METHODS
  A total of 247 measurements on 96 MDCT scanners were collected using a standard CT dose index (CTDI) measurement protocol. The scan parameters used in the measurements (tube voltage, milliampere-seconds [mAs], and detector-channel configuration) were set according to trial protocol for average size subjects. The normalized weighted CT dose index (CTDI(w)) (computed as CTDI(w)/mAs) obtained from each trial-participating scanner was tabulated.
  
  
  RESULTS
  We found a statistically significant difference in normalized CT dose index among CT scanner manufacturers, likely as a result of design differences, such as filtration, bow-tie design, and geometry. Our findings also indicated a statistically significant difference in normalized CT dose index among CT scanner models from the same manufacturer (e.g., GE Healthcare, Siemens Healthcare, and Philips Healthcare). We also found a statistically significant difference in normalized CT dose index among all models and all manufacturers; furthermore, we found a statistically significant difference in normalized CT dose index among CT scanners from all manufacturers when we compared scanners with four or eight data channels to those with 16, 32, or 64 channels, suggesting that more complex scanners have improved dose efficiency.
  
  
  CONCLUSIONS
  Average normalized CT dose index values varied by a factor of almost two for all scanners from all manufacturers. This study was focused on machine-specific normalized CT dose index; patient dose and image quality were not addressed.
authors.affiliation: Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. dcody@mdanderson.org
authors.forename: Dianna D
authors.initials: DD
authors.lastname: Cody
authors.forename: Hyun-Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Cagnon
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Larke
authors.forename: Michael M
authors.initials: MM
authors.lastname: McNitt-Gray
authors.forename: Randell L
authors.initials: RL
authors.lastname: Kruger
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Flynn
authors.forename: J Anthony
authors.initials: JA
authors.lastname: Seibert
authors.forename: Philip F
authors.initials: PF
authors.lastname: Judy
authors.forename: Xizeng
authors.initials: X
authors.lastname: Wu
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D011785:Quality Assurance, Health Care; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D015898:Tomography Scanners, X-Ray Computed / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000592:standards*; D014481:United States