Published Online:

For 545 adult patients who underwent CT examinations of the torso and who varied in size by a factor of two, the automatic exposure control system used increased CTDIvol from 12 to 26 mGy, but average estimated patient dose was 22 mGy ±?3, independent of size.


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.

Materials and 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 (CTDIvol) 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 CTDIvol and SSDE on patient size.


Patient sizes ranged from 42 to 84 cm. In this range,CTDIvol was significantly correlated with size (slope = 0.34 mGy/cm; 95% confidence interval [CI]: 0.31, 0.37 mGy/cm; R2 = 0.48; P < .001), but SSDE was independent of size (slope = 0.02 mGy/cm; 95% CI: −0.02, 0.07 mGy/cm; R2 = 0.003; P = .3). These R2 values indicated that patient size explained 48% of the observed variability in CTDIvol but less than 1% of the observed variability in SSDE. The regression of CTDIvol versus patient size demonstrated that, in the 42–84-cm range, CTDIvol 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.


For the evaluated automatic exposure control system,CTDIvol (scanner output) increased linearly with patient size; however, patient dose (as indicated by SSDE) was independent of size.

© RSNA, 2012


  • 1 Gies M, Kalender WA, Wolf H, Suess C, Madsen M. Dose reduction in CT by anatomically adapted tube current modulation. I. Simulation studies. Med Phys 1999;26(11):2235–2247. Crossref, MedlineGoogle Scholar
  • 2 Kalra MK, Maher MM, Toth TL, et al.. Strategies for CT radiation dose optimization. Radiology 2004;230(3):619–628. LinkGoogle Scholar
  • 3 Kalra MK, Rizzo SM, Novelline RA. Reducing radiation dose in emergency computed tomography with automatic exposure control techniques. Emerg Radiol 2005;11(5):267–274. Crossref, MedlineGoogle Scholar
  • 4 McCollough CH, Bruesewitz MR, Kofler JM. CT dose reduction and dose management tools: overview of available options. RadioGraphics 2006;26(2):503–512. LinkGoogle Scholar
  • 5 Rizzo S, Kalra M, Schmidt B, et al.. Comparison of angular and combined automatic tube current modulation techniques with constant tube current CT of the abdomen and pelvis. AJR Am J Roentgenol 2006;186(3):673–679. Crossref, MedlineGoogle Scholar
  • 6 Söderberg M, Gunnarsson M. Automatic exposure control in computed tomography—an evaluation of systems from different manufacturers. Acta Radiol 2010;51(6):625–634. Crossref, MedlineGoogle Scholar
  • 7 Bauhs JA, Vrieze TJ, Primak AN, Bruesewitz MR, McCollough CH. CT dosimetry: comparison of measurement techniques and devices. RadioGraphics 2008;28(1):245–253. LinkGoogle Scholar
  • 8 Shope TB, Gagne RM, Johnson GC. A method for describing the doses delivered by transmission x-ray computed tomography. Med Phys 1981;8(4):488–495. Crossref, MedlineGoogle Scholar
  • 9 McNitt-Gray MF. AAPM/RSNA Physics Tutorial for Residents: Topics in CT. Radiation dose in CT. RadioGraphics 2002;22(6):1541–1553. LinkGoogle Scholar
  • 10 McCollough CH, Leng S, Yu L, Cody DD, Boone JM, McNitt-Gray MF. CT dose index and patient dose: they are not the same thing. Radiology 2011;259(2):311–316. LinkGoogle Scholar
  • 11 International Electrotechnical Commission. Medical Electrical Equipment. Part 2–44: Particular requirements for the safety of x-ray equipment for computed tomography. IEC publication No. 60601-2-44. 3rd ed. Geneva, Switzerland: International Electrotechnical Commission (IEC) Central Office, 2012. Google Scholar
  • 12 American Association of Physicists in Medicine. Standardized methods for measuring diagnostic x-ray exposures. New York, NY: American Association of Physicists in Medicine, 1990. Google Scholar
  • 13 European Commission. European guidelines on quality criteria for computed tomography (EUR 16262 EN). Luxembourg: European Commission & The Office For Official Publications of the European Communities, 2000. Google Scholar
  • 14 Valentin J; International Commission on Radiation Protection. Managing patient dose in multi-detector computed tomography (MDCT). ICRP Publication 102. Ann ICRP 2007;37(1):1–79, iii. CrossrefGoogle Scholar
  • 15 American Association of Physicists in Medicine. The measurement, reporting and management of radiation dose in CT (Report #96). In: AAPM Task Group 23 of the Diagnostic Imaging Council CT Committee. College Park, Md: American Association of Physicists in Medicine, 2008. Google Scholar
  • 16 American Association of Physicists in Medicine.Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations (Task Group 204). College Park, Md: American Association of Physicists in Medicine, 2011. Google Scholar
  • 17 Mackinnon JG, White H. Some heteroskedasticity-consistent covariance-matrix estimators with improved finite-sample properties. J Econom 1985;29(3):305–325. CrossrefGoogle Scholar
  • 18 Israel GM, Cicchiello L, Brink J, Huda W. Patient size and radiation exposure in thoracic, pelvic, and abdominal CT examinations performed with automatic exposure control. AJR Am J Roentgenol 2010;195(6):1342–1346. Crossref, MedlineGoogle Scholar
  • 19 Schindera ST, Nelson RC, Toth TL, et al.. Effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation: phantom study. AJR Am J Roentgenol 2008;190(2):W100–W105. Crossref, MedlineGoogle Scholar
  • 20 McCollough C, Yu L. Unintentional errors in CT imaging with use of a constant noise automatic exposure control (AEC) paradigm [abstr]. In: Radiological Society of North America Scientific Assembly and Annual Meeting Program. Oak Brook, Ill: Radiological Society of North America, 2008. Google Scholar
  • 21 Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Washington, DC: National Academies Press, 2006. Google Scholar
  • 22 American Association of Physicists in Medicine. AAPM Position Statement on Radiation Risks from Medical Imaging Procedures (Policy No. PP 25-A). = 318&type = PP&current = true. 2011. Google Scholar
  • 23 Health Physics Society. Radiation risk in perspective. Position Statement of the Health Physics Society. PS010–1. McLean, Va: Health Physics Society, 2004. Google Scholar
  • 24 Turner AC, Zhang D, Khatonabadi M, et al.. The feasibility of patient size-corrected, scanner-independent organ dose estimates for abdominal CT exams. Med Phys 2011;38(2):820–829. Crossref, MedlineGoogle Scholar

Article History

Received November 7, 2011; revision requested December 19; revision received May 15, 2012; accepted June 8; final version accepted June 25.
Published online: Dec 2012
Published in print: Dec 2012