title: Size-specific dose estimates for adult patients at CT of the torso.
abstract: OBJECTIVE
  To determine relationships among patient size, scanner radiation output, and size-specific dose estimates (SSDEs) for adults who underwent computed tomography (CT) of the torso.
  
  
  METHODS
  Informed consent was waived for this institutional review board-approved study of existing data from 545 adult patients (322 men, 223 women) who underwent clinically indicated CT of the torso between April 1, 2007, and May 13, 2007. Automatic exposure control was used to adjust scanner output for each patient according to the measured CT attenuation. The volume CT dose index (CTDI(vol)) was used with measurements of patient size (anterioposterior plus lateral dimensions) and the conversion factors from the American Association of Physicists in Medicine Report 204 to determine SSDE. Linear regression models were used to assess the dependence of CTDI(vol) and SSDE on patient size.
  
  
  RESULTS
  Patient sizes ranged from 42 to 84 cm. In this range,CTDI(vol) was significantly correlated with size (slope = 0.34 mGy/cm; 95% confidence interval [CI]: 0.31, 0.37 mGy/cm; R(2) = 0.48; P < .001), but SSDE was independent of size (slope = 0.02 mGy/cm; 95% CI: -0.02, 0.07 mGy/cm; R(2) = 0.003; P = .3). These R(2) values indicated that patient size explained 48% of the observed variability in CTDI(vol) but less than 1% of the observed variability in SSDE. The regression of CTDI(vol) versus patient size demonstrated that, in the 42-84-cm range, CTDI(vol) varied from 12 to 26 mGy. However, use of the evaluated automatic exposure control system to adjust scanner output for patient size resulted in SSDE values that were independent of size.
  
  
  CONCLUSIONS
  For the evaluated automatic exposure control system,CTDI(vol) (scanner output) increased linearly with patient size; however, patient dose (as indicated by SSDE) was independent of size.
authors.affiliation: Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
authors.forename: Jodie A
authors.initials: JA
authors.lastname: Christner
authors.forename: Natalie N
authors.initials: NN
authors.lastname: Braun
authors.forename: Megan C
authors.initials: MC
authors.lastname: Jacobsen
authors.forename: Rickey E
authors.initials: RE
authors.lastname: Carter
authors.forename: James M
authors.initials: JM
authors.lastname: Kofler
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D049628:Body Size; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011835:Radiation Protection; D013902:Radiography, Thoracic; D011874:Radiometry; D014057:Tomography, X-Ray Computed