Basics of Radiation ExposureSo, what the heck is a "millisievert" and how do you keep from racking up 100, 200, or 1,000 of them? A millisievert is the scientific unit of measurement for radiation dose. Since different parts of the body have different degrees of sensitivity to radiation, exposure is generally expressed as the "effective dose." For example, let's say Organ X and Organ Y are each exposed to 10 mSv of radiation. However, Organ Y is twice as sensitive. The actual dose would be 10 mSv for each organ, but the effective dose would be 10 mSv for Organ X and 20 mSv for Organ Y.
The Bad News about Radiation ExposureThe bad news is that about 80% of our radiation exposure comes from natural, unavoidable sources. The average American receives an effective dose of approximately 3 mSv of radiation each year from radon, rocks, outer space, soil, electronics, and airplane travel. (Before you swear off of airplanes, keep in mind that you get about 1 mSv of exposure for every 200 hours of flight time.)
The Good News about Radiation ExposureThe good news is that it takes a lot of radiation exposure to get to the levels that cause cancer. Once you know the numbers, you can avoid unnecessarily exposing yourself to extra sources of radiation. For example, if you're concerned about radiation exposure, you may want to choose to have a colonoscopy (no radiation exposure) instead of a barium enema (about 7 mSv of radiation exposure).
Effective doses for common sources of radiation include the following:
- Airplane travel (0.005 mSv/hour)
- Barium enema (7 mSv)
- Chest X-ray (0.10 mSv)
- CT scan of abdomen (10 mSv)
- CT scan of chest (8 mSv)
- CT scan of head (2 mSv)
- Dental X-ray (0.09 mSv)
- Mammogram (0.7 mSv)
- X-ray of skull (0.07 mSv)
- Whole-body CT scan (10 mSv)
- Nordenberg, Tamar. The Picture of Health: It's What's Inside That Counts with X-rays, Other Imaging Methods. U.S. Food and Drug Administration. Feb. 1999. 27 Aug. 2006 [http://www.fda.gov/fdac/features/1999/199_xray.html].
- Radiation Exposure in X-ray Examinations. Radiology Info. 27 Aug. 2006 [http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray].
- Radiation Injury. Merck Manual of Medical Information. 1 Feb. 2003. 27 Aug. 2006 [http://www.merck.com/mmhe/sec24/ch292/ch292a.html].
- Report on Carcinogens, 11th Edition. Public Health Service. 27 Aug. 2006 [http://ntp-server.niehs.nih.gov/ntp/roc/toc11.html].
- What are the Radiation Risks from CT? Center for Devices and Radiological Health. 4 May 2005. 27 Aug. 2006 [http://www.fda.gov/cdrh/ct/risks.html].