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COMPUTED TOMOGRAPHY (CT) X-RAY EXAMS:
Estimated Doses to Patients

XaHP Document 112, September 2001





TOPIC TYPE OF DOSE ESTIMATED DOSE SOURCE Eff.Dose: CT/flying
Extra radiation during commercial airplane flights within USA. "Effective" dose/hr. And
per 10 hours.
0.0003 cSv per hour. And
0.003 cSv per 10 hours.
UNSCEAR 1993, p.38.  
CT scans, general. Tissue dose per scan. 1-3 cSv. Mettler 2000, p.352.  
CT head scan, adult. Surface dose. 3-7 cGy (rads). Nickoloff 2001, p.285.  
CT head scan, adult. "Effective" dose. 0.15 cSv. Mettler 2000, p.352. 50 to 1.
CT chest, typical. * Surface dose. 2-5 cGy (rads). Nickoloff 2001, p.286.  
CT chest, typical. Internal dose. Below 2 cGy (rads). Ravenel 2001, p.283.  
CT chest, typical. "Effective" dose. 0.54 cSv. Huda 2000, p.843. 180 to 1.
CT chest, unspecified. ** Breast: Mean glandular dose. Up to 5 cGy (rads). Gray 1998-a, p.63.  
CT multi-slice of heart for calcium score. Surface dose. Up to 10-20 cGy. Nickoloff 2001, p.286.  
CT chest angiograph. Surface dose. 2-4 cGy (rads). Nickoloff 2001, p.286.  
CT chest, cancer screening. Surface dose. 0.2 - 0.4 cGy (rad). Nickoloff 2001, p.286.  
Electron Beam CT chest angiography or cardiac calcium score. "EBCT." X-ray beam travels from back to front. Reduced dose to breasts and front chest wall. Nickoloff 2001, p.286.  
CT abdominal "series." Surface dose. 2-5 cGy (rads). Nickoloff 2001, p.285.  
CT abdominal, adult. "Effective" dose. 0.39 cSv. Ware 1999, p.64. 130 to 1.
 Young adult. "Effective" dose. 0.44 cSv. Ware 1999, p.64. 147 to 1.
 Child. "Effective" dose. 0.61 cSv. Ware 1999, p.64. 203 to 1.
CT-fluoroscopy, for imaging in biopsies, etc. Range of typical dose-rates. 20-60 cGy (rads) per minute. Nickoloff 2001, p.285.  





Page 2 of XaHP Document #112, September 2001:
Estimated Doses to Patients from CT X-Ray Examinations.


 

Real Dose vs. "Effective" Dose

A real dose (dose-unit = cGy or rad) reflects something objective: The energy deposited by x-rays per gram of irradiated body-tissue. By conrast, an "effective" dose is a calculation which estimates what dose, if given to the entire body, might produce approximately the same amount of risk as would the real dose actually received by the irradiated sections. "Effective" doses (dose-unit = cSv or rem) incorporate a crude adjustment for the different types of ionizing radiation, plus "tissue weighting factors" which attempt (despite woefully inadequate evidence) to assess the attributable probability of fatal cancer in different organs, the additional detriment from non-fatal cancer and hereditary disorders, and the different latency periods for cancers in various tissues.

Footnote * Dose-Comparison.

The typical chest CT exam must not be confused with the typical chest film. The back-to-front chest film delivers a surface entrance dose of about 0.02 cGy (rad), which is at least 100 times lower than the reported dose-range of 2-5 cGy (rads) for the typical chest CT exam.

Footnote ** Dose-Comparison

The breasts receive a mean glandular dose of x-rays "up to 5 cGy (rads)" from chest CT exams. By comparison, the mean glandular breast-dose from a complete 2-view mammographic screening exam is about 0.2 cGy (rad). Mammographic doses vary with the thickness of the compressed breasts. Thicker breasts require higher doses.

Full-Body CT Screening Exam

The table on page 1 contains no entry for the recently introduced full-body CT screening exam because dose-estimates vary widely. This type of exam is briefly discussed in Nickoloff 2001, p.287.

 

References for Pages 1 and 2



XaHP: The X-rays and Health Project.
      An educational project of the
      Committee for Nuclear Responsibility.
      E-mail: comments@x-raysandhealth.org
      Web: www.x-raysandhealth.org
Post Office Box 421993
San Francisco CA 94142-1993.
      Gifts are tax-deductible.

The plan:  Lower x-ray doses per x-ray procedure.
The result:  Fewer cases of x-ray-induced cancer
and coronary heart disease.



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