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SIDEBAR: Radiation Facts and Comparisons

Radiation Facts
The radiation received in 2 full-body CT scans has now been found to be equivalent to the lowest average doses received by Japanese atomic-bomb survivors and nuclear industry radiation workers, about 20 milliesieverts. Another way to think of this is that in a normal environment, people are exposed to 3-5 m milliesieverts of radiation per year from things like radon gas in their homes, computer and TV screens and cosmic rays. (The variation depends on proximity to power plans and on altitude: higher up = less atmospheric protection = more radiation).

That said, it is almost impossible for the average person to find out how much radiation they’d be getting in any particular CT scan:

  • With the exception of mammography, radiation doses are not regulated by federal law.10
  • Even with the same CT settings, different scanners will produce different doses and therefore different risks—we who is we estimate by up to 35%.11
  • The FDA12, the Radiological Society of North America13, and scientific researchers14 report varying dose measurements for the same scans and disagree over which way of measuring – by organ or by entire body – is more relevant.
  • A CT scan can get repeated multiple times in the course of a single diagnostic study and radiation doses can overlap in multislice scanners15.
  • Age and repeated exposure also complicates the issue: people who were first scanned as young adults, and thus assumedly have a longer remaining lifetime in which to get scanned again, will have higher cancer risks.
  • There is little evidence regarding whether different body organs respond differently to radiation.
  • What is known is half of diagnostic CT examinations in adults are scans of the body, and about 1/3 are scans of the head, with about 75% obtained in a hospital setting and 25% in a single-specialty practice setting.
SIDEBAR: Radiation Comparisons
Source of Radiation Average Amount
(mSv = millisieverts)
How It Compares
Lowest average doses received by Japanese atomic-bomb survivors and nuclear industry radiation workers 20 mSv throughout the body = 2 full-body CTs
Full-body CT 16 mSv to the lung, 14 mSv to the digestive organs, 10 mSv to the bone marrow
= 12 mSv weighted average throughout body
= 100 mammograms
Lower GI X-ray with barium enema 15 mSv to the colon
= 4-7 mSv weighted average throughout body
= at least 1.5 years of natural environmental radiation
Adult abdominal CT 10 mSv to the stomach
= 10 mSv weighted average throughout body
= 3 years of natural environmental radiation
Chest CT 8 mSv =100-400 chest x-rays
=10-25 mammograms
CT pulmonary angiogram ? 7 mammograms
Normal environment (radon gas in homes, cosmic rays, TV/computer screens) 3-5 mSv to the whole body per year, depending on altitude (higher up = less atmospheric protection = more radiation) = like getting a chest x-ray once a week
Mammography 2.6 mSV to the breast
=.13 to .7 mSV to the whole body
Chest X-ray .01 to .15 mSv to the lung
Dental X-ray .005 mSv to the brain
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