Radiation Exposure

Radiation Exposure in Radiology

Radiation exposure can be a complicated topic with technical terms and various units of dosage and exposure. The following summarizes available information and compares exposure from x-ray studies to that from naturally occurring sources.

X-rays are a form of electromagnetic radiation identical to – though more energetic than – common forms of radiation such as light, ultraviolet rays, and radio waves. Radiation exposure is measured as the amount of energy absorbed by the body per unit mass. The most common units of exposure are the milliSievert (mSv) or the rem. (1 rem = 10 mSv.) The most easily understood effect of radiation on humans is predictable and dose related and occurs only at doses much higher than those in diagnostic imaging. These changes of the skin, bone marrow, and GI tract virtually never occur from standard diagnostic x-rays.

The second and more concerning risk from radiation is chromosomal damage that could cause cancer years after the exposure. No one knows for certain what the exact risk is, and there is no direct evidence of cancer caused by the levels of diagnostic x-ray exposure. Potential risks have been extrapolated from groups with massive exposures, particularly those irradiated in atomic blasts. The conservative decision of the medical community is to assume a linear relationship of risk to radiation exposure even down to the lowest levels of x-ray exposure.

To understand relative radiation exposures and risk, consider common radiation exposures:

	Exposure per year (mSv)
Natural (earth, radon, cosmic rays) in Boston	3
in Denver	6
Flying across country one way	.06
Live next door to nuclear power plant	.02
Watching color TV	.03

The average person in the U.S. receives a yearly radiation dose of 3 mSv from natural radiation sources (55% of which is from radon) and cosmic radiation. Compare this natural background radiation exposure to typical radiation doses for diagnostic studies.

Type X-Ray	Exposure (mSv)	Comparable to natural background radiation for:
Chest – PA and Lat	0.06	6 days
Extremity	0.06	6 days
Thoracic Spine	0.7 - 1.4	3 months
Lumbar Spine	1.0 - 1.8	3 months
Pelvis AP	0.7	2 months
IVP	1.5-2.5	6 months
Upper GI	2 - 3	8 months
Barium Enema	4 - 7	16 months
Mammogram	0.13	1 month
CT Head	2	8 months
CT Chest	8	3 years
CT Abdomen	10	3 years

Because of the relative high lifetime risk of developing cancer from other causes, no one has been able to show any increased cancer risk from radiation exposure less than 100 mSv. Nonetheless, the cautious medical approach is to assume some cancer risk even at low radiation exposure. Extrapolating from the rates at high exposure, the International Commission on Radiological Protection gives an upper limit of increased cancer incidence of 0.005% per mSv exposure. This means that for a CT scan of the abdomen, the increased lifetime risk of cancer would be no greater than 0.05%. Given that the average total lifetime cancer risk in the U.S. is 25%, having an abdominal CT increases expected risk from 25 to 25.05%. Compared to other lifestyle factors such as smoking, alcohol use, sun exposure, diet, and exposure to asbestos or pesticides, the risk from routine medical radiation is quite low and essentially impossible to prove in any individual case.

This does not minimize, however, our concern for radiation exposure in medical imaging. The goal for every exam is to use a dose As Low As Reasonably Achievable (ALARA). To reduce exposure, we will only image with x-rays when care providers believe that the health benefit outweighs the assumed risks, and we will image only the region of concern.

If you have further concerns about x-ray exposure, you can discuss them with your personal physician before the exam. Radiology technicians and radiologists can also answer specific questions in the department. During pregnancy there are other concerns regarding fetal exposure. If you are possibly pregnant, please inform your doctor and the radiology staff prior to your exam. For more information on x-rays during pregnancy, select the document “Radiation Exposure During Pregnancy” from the department web page.

Two excellent internet references are:

Radiation and Health Physics Page
RadiologyInfo

M. Rizzo 10/2005

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