What We Don’t Know About Imaging Test Radiation–A Lot

File this one in our ongoing series about miscommunication between doctors and patients. This time the subject is radiation and how little most patients know about it.

Last week we posted an item about how doctors sometimes mislead, even lie, to their patients when discussing the risks and benefits of certain treatments or mistakes they might have made.

A research letter recently published in the Archives of Internal Medicine, concluded that many patients undergoing diagnostic imaging don’t understand that it often involves radiation. And that the risks of radiation might be more than they think.

The researchers analyzed the use of CT and SPECT scans. CT (computed tomography) scans create cross-section images of the body using X-rays. Depending on the test, they can involve injecting a contrast dye to illuminate certain areas of the body. SPECT (single-photon emission computerized tomography) scans are a more specific test using nuclear images-the radioactive dye and a special camera create 3-D pictures of how certain organs are functioning. An X-ray can show bone and tissue structure, but a SPECT scan shows how blood flows to a certain organ.

The risks of any kind of CT scan include allergic reactions to the dye, and exposure to radiation. According to the National Institutes of Health, CT scans expose you to a lot more radiation than regular X-rays, and having several of either over time might increase your risk for cancer. To learn more, see our backgrounder on radiation overdose injuries.

The amount of radiation you receive during a CT scan depends on the body part being tested. According to the Health Physics Society, a nonprofit scientific professional organization devoted to the science and practice of radiation safety, and composed of some 5,500 scientists, physicians, engineers and lawyers, the averages for certain CT scans are:

  • head-2.0 mSv
  • chest-7.0 mSv
  • abdomen/pelvis-10.0 mSv
  • whole body-10.2mSv

The dose from a standard chest X-ray (two views, front and side) is 0.1 mSv. That means a chest CT scan with 7.0 mSv’s has the same X-ray dose as 70 chest X-rays.

Some other authoritative resources say certain scans use more radiation. The Associated Radiologists of New Jersey say some chest or abdominal scans can approach 18 mSv.

The designation mSv is an abbreviation for millisieverts, the scientific unit of measurement for radiation dose (commonly referred to as “effective dose”). The average exposure from background radiation (originating not from tests or, for example, airport security screenings, but the natural environment), is about 3 mSv per year; more if you live at high elevation.

So a single abdominal CT scan exposes you to three to six times the amount of radiation you otherwise would be exposed to in a year.

Researchers surveyed several hundred randomly selected, nonurgent outpatients at a major academic medical center for most of 2011. They asked 16 questions to assess patient knowledge and perceptions about health risks and benefits from CT or cardiac SPECT. One question asked if the scan they were about to undergo exposed their body to radiation. Only if patients responded “yes” were they instructed to continue answering five additional questions assessing their knowledge and perceptions of radiation.

One-third of all patients did not know that the scan exposed their body to radiation. Of the 154 patients who did, nearly half said their health-care provider had informed them of the radiation.

Nearly 7 in 10 respondents said their health-care provider was their main source of health information. About half had heard nothing in the media over the past year about radiation from medical imaging. Two-thirds believed that their scan was definitely necessary; half believed the results would help them feel better, and nearly as many believed the test would enable them to live longer. Only 3 in 100 reported thinking about radiation before their scan.

Nine in 10 patients said that it was important to be informed of imaging risks, and more than 8 in 10 said that the health-care provider who ordered the scan explained the reason(s) for it.

When the patients were asked to compare radiation from their scan with a year’s worth of background radiation, 85 in 100 underestimated the amount of radiation. Even more than that said they weren’t worried about scan radiation. Only 5 in 100 believed that scan radiation would increase their lifetime risk of cancer, and 95 in 100 said it was more important to figure out what might be wrong than to worry about scan radiation.

As the researchers wrote, “A well-informed patient has an understanding of radiation dose and potential health risks of radiation prior to imaging. When combined with an understanding of benefits, patients are well positioned to assess the risk-benefit ratio and participate in shared decision-making.”

Why are patients so ill-informed? Many health-care providers, the researchers suggested, have little knowledge themselves about radiation, so they’re not equipped to educate their patients. And because radiation is difficult to explain and comprehend, some patients might be unable to grasp the whole picture during a short clinical visit.

Because so many people appear to be unaware of scan radiation, and because those who are appear to have an inaccurate sense of it, it’s important that if your doctor suggests such a diagnostic test, you be assured that it’s necessary and that the diagnostic benefit is greater than the risks. And always understand that a test is not a treatment. CT scans find a problem, they don’t solve it.

Here’s a good website from the American Society of Radiation Technologists that lets you calculate your X-ray exposure and risk from various types of imaging studies.

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