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Do CT Scans Cause Cancer?

By December 6, 2010

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Many types of imaging tests, such as x-rays and CT scans, expose us to radiation. Typically, the amount of radiation is small enough that it doesn't pose a measurable risk to health. When people have multiple scans, however, the radiation exposures can start to add up.

This has raised concern among health experts that CT scans, which may use more radiation than conventional x-rays, can contribute to increased risk of cancer in people who get these scans. A new study provides reassurance that the risk is small.

Do More Scans Mean More Cancer?

Last year, the National Council on Radiation Protection and Measurement issued a report which detailed that Americans receive seven times more radiation from diagnostic scans today than they did in 1980. A recent article in the Journal of the American Medical Association (JAMA) found that use of advanced imaging in emergency departments, which includes CT scans, tripled between 1998 and 2007.

These numbers point to a clear trend of more CT scans and high-tech imaging methods in recent years. To study the potential connection between CT scans and cancer risk, researchers used Medicare data from two time periods - 1998-2001 and 2002-2005. A total of 10.8 million people were included in this study.

42% of people in the first time period had at least 1 CT scan and 49% of people in the second time period had 1 or more scans. Abdominal scans accounted for the most total radiation exposure in these groups. Using a well-accepted statistical method (the BEIR VII model) to assess radiation exposures and cancer risk, the researchers found that:

  • 0.02% of cancers in the group studied during the first time period were due to radiation exposure from CT scans
  • 0.04% of cancers in the group studied during the second time period were due to radiation exposure from CT scans

Lower than Expected, Still a Concern

Dr. Pat Basu, the lead researcher on the study, indicated that these numbers were lower than expected. He pointed out however, "...while the risk of secondary cancers appears to be lower than we thought, we still have to monitor our use of such imaging and keep track of the consequences."

Safer CT Scans

The bottom line is that the number isn't zero, which means more work needs to be done to make these scans safer. Fortunately, experts on medical imaging expect that within the next few years, new CT machines  will become available. These machines are projected to reduce the amount of radiation delivered during the scan by 10 to 100 fold.

Dr. Basu urged that patients should be told not to be afraid of getting a CT scan if there is a medically appropriate reason. However, some scans may be ordered for financial reasons, such as a way for a health care centers to generate more fees. People need to take care of themselves and make sure the CT scan really is necessary. Some scans are, others are not.

If you need a CT scan, consider whether you've had them before. If not, a single scan is unlikely to expose you to additional cancer risk. If you've had many medical tests that expose you to radiation, discuss this with your doctor. There may be other options for getting the information needed to guide your medical care and cancer treatment decisions.

Source

Radiological Society of North America (RSNA) 96th Scientific Assembly and Annual Meeting: Abstract SSK08-04 Presented December 1, 2010.

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