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Radiation from Exams Adds Up to Increased Risk of Cancer

CT Scan and cancer risk

Each year many medical exams involving radiation are done. These tests include x-rays, fluoroscopy, computed tomography (CT) scans, and nuclear medicine scans.

The radiation exposure adds up over the years with each exam. Radiation exposure can lead to increased cancer rates in years to come.

Reza Fazel, M.D and colleagues have published a study in the New England Journal of Medicine which looked at the additive effect of radiation over the years. The researchers utilized claims data from UnitedHealthcare on nearly one million adults aged 18 to 65 years old in five regions across the United States to estimate the overall rates of exposure to radiation from medical imaging procedures over a three-year period (2005 through 2007).

While many medical tests are clearly necessary - and the benefits of the test outweigh the risk of the radiation - in other cases it’s less clear.

A perspective piece that accompanies the study calls for a much more cautious approach, with more study of the benefits of imaging tests before they are put into widespread use.

“We have to think and talk explicitly about the elements of danger in exposing our patients to radiation,” writes the piece’s author, an NIH doc named Michael Lauer. What’s more, he argues, doctors should weigh a patient’s previous history of high-radiation tests and explain the possibility year after year of high-radiation testing could lead to cancer.

Levels of radiation exposure were categorized by the authors as:

* 'low', less than 3 millisieverts per year, roughly the annual background level from natural sources in the US

* 'moderate', up to 20 millisieverts per year, the 5-year-annual average limit for occupational exposure

* 'high', up to 50 millisieverts per year, the annual limit for occupational exposure

* 'very high' more than 50 millisieverts per year

During the study period, 655,613 enrollees (68.8%) underwent at least one imaging procedure associated with radiation exposure. The mean cumulative effective dose from imaging procedures was 2.4±6.0 mSv per enrollee per year.

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Moderate effective doses of radiation were incurred in 193.8 enrollees per 1000 per year. High and very high doses were incurred in 18.6 and 1.9 enrollees per 1000 per year, respectively.

Computed tomographic and nuclear imaging accounted for 75.4% of the cumulative effective dose, with 81.8% of the total administered in outpatient settings.

Cardiac stress testing was the procedure that exposed patients to the highest radiation levels, an average of 15.6 mSv, and accounted for 22% of all radiation exposure. CT scans of the abdomen, which typically produce about 8 mSv, accounted for more than 18% of exposure. A mammogram -- a single X-ray -- produces about 0.4 mSv.

This study confirmed the one released in March of this year by the National Council for Radiation Protection which stated “that in 2006, Americans were exposed to more than seven times as much radiation from medical procedures than they were in the early 1980s.”

The increased radiation exposure can lead to increased cancer rates in years to come. As many as 7 percent of patients will have enough radiation exposure from CT scans during their lifetime to slightly raise their risk of cancer.

What you as the patient can do:

Keep a record of your X-ray history. Before undergoing a scan, should ask your physician:

* Why do I need this exam?

* How will having this exam improve my health care?

* Are there alternatives that do not use radiation which are equally as good?

* Is my child receiving a “kid-sized” radiation dose? (for pediatric exams)

Related story
Are Patients In U.S. Over-Exposed?, Personal Health

Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures; New England Journ of Med, Vol 361:849-857, August 27, 2009, No 9.

Emory University School of Medicine News Release