Getting Burned: Radiation Exposure from CT Scans

Taken from the May/June 2006 issue of the Women's Health Activist Newsletter.

Everyone is exposed to some radiation from rocks, radon, cosmic rays, food, and water. The average background radiation exposure from natural radiation in the U.S. is about 3 millisieverts (mSv). (Radiation doses are commonly described in millisieverts [mSv] or milligrays [mGy], both measures of the energy absorbed by body tissues.) Proximity to power plants, computer screens, TVs, and other electronics also exposes us to small amounts of radiation.1 But, more than 3/4 of radiation exposure from non-natural sources comes from medical use of radiation, such as X-rays and Computed Tomography scans.

Computed Tomography scans (or CT, pronounced “cat” scans) use multiple X-rays to create a three-dimensional image of the body. The scans can be very good diagnostic tools, but are vastly overused, with over 60 million performed in the U.S. annually.2 CT scans use far more radiation than conventional X-rays and are estimated to be responsible for 70% of medical radiation exposure.2 A single CT scan for a suspected kidney stone exposes a patient to a radiation dose of 6.5--8.5 MSv. Many people receive multiple scans; one six-year study of 4,562 patients found that 176 (4%) people had been exposed to cumulative radiation doses of 20--154 mSv.3

A 2005 National Academy of Science report estimates that one individual in 1,000 develops cancer from exposure to a 10 mSv dose of radiation.1 In fact, 1945 Nagasaki bombing survivors who were exposed to radiation doses between 5--200 mSv demonstrated increased cancer rates. Breasts, thyroid glands, and eyes are particularly sensitive to the cancer-causing effects of radiation. While some women worry about the radiation exposure from mammograms, radiation that’s not specifically directed at the breasts exposes these tissues to more radiation exposure than mammograms do. A chest CT scan, for example, exposes breasts to a radiation dose of 20--50 mGy, equivalent to 100--400 chest X-rays or 10--25 mammograms. A CT pulmonary angiogram (to diagnose blood clots in the lungs) exposes breasts to over seven times more radiation than a mammogram does.4 A single screening mammogram provides 3 mSv of radiation, while a full-body CT scan provides a radiation dose almost 100 times higher.5

Not that anyone should actually get a full-body (or whole-body) CT scan, which are being inappropriately promoted as good preventive medicine and are often available at your local shopping mall. A 2003 survey identified 88 radiologic screening centers that offered full-body CT scans ranging in price from $795-- $1,215. Full-body CT scans are particularly popular in California, which had 30 centers, and New York, with 13.6 There are undoubtedly more of these money-grubbing centers operating today.

There’s no excuse for this sort of shotgun approach to diagnosis, especially when the diagnostic procedure itself is carcinogenic. And, while there is good evidence that screening mammograms reduce breast cancer deaths among menopausal women, there’s no evidence that whole-body CT scans save lives. There’s actually reason to worry that the opposite may be true. It’s been estimated that a 45-year-old adult who had annual full-body CT scans until age 75 raises her lifetime cancer risk by about 2%. Just one exam raises a person’s cancer risk by 0.08%, or one case of cancer  for every 1,250 people exposed).7

The cancer-causing effects of CT scans are not well-known, even among physicians who regularly order or interpret these scans. One study interviewed patients who came to an Emergency Department (ED) with abdominal or flank pain and who had received a diagnostic CT scan. The patients were asked if the risks and benefits of CT scans had been explained to them, if radiation doses had been mentioned, and if they believed that CT scans increased the lifetime risk of cancer.8 Participants were then asked to estimate a CT scan’s radiation dose, compared to a chest X-ray. ED doctors (who routinely order diagnostic CT scans) and radiologists (who interpret the scans) were also asked variations on these questions.

Only 3% of patients and 9% of ED docs knew that CT scans increased the lifetime risk of cancer; amazingly, only 47% of radiologists surveyed answered the cancer risk question correctly. On estimates of radiation doses from CT scans vs. chest X-ray, most believed that CT scans provided 2--10 times the radiation dose of a chest X-ray (64% of patients, 44% of ED docs, and 56% of radiologists chose this answer from five options). In truth, CT scans provide a radiation dose 100--250 times higher than a chest X-ray. Only 22% of the ED docs and 13% of radiologists got it right (none of the patients guessed that high). Understandably, patients were not informed of risks unknown to their doctors: 78% of the ED docs stated that they had not outlined risks and benefits of CT scan radiation to patients. Almost all (93%) patients reported that CT scans’ risks and benefits had not been outlined to them.8

Ironically, patients are routinely asked to sign a consent form that tells them about rare but serious complications and deaths (1 in 400,000) caused by the iodinated contrast material often injected during CT scans. The forms usually do not mention cancer risk, which is probably far more common (although it may occur many years later).9

In some cases, CT scans can save lives but, in many cases, other radiologic diagnostics can be used that do not involve tissue-damaging radiation. Ultrasound and Magnetic Resonance Imaging MRI) both use non-ionizing radiation; these tools can sometimes be combined with conventional (plain-film) X-rays to provide diagnostic accuracy similar to that of a CT scan.


Adriane Fugh-Berman, MD, is a former NWHN Board Chair whose research presents a critical analysis of the marketing of prescription drugs. Adriane educates prescribers on pharmaceutical marketing practices as Director of the PharmedOUT program, and created the Health in the Public Interest program at Georgetown University School of Medicine where she trains a new generation of consumer advocates.

Read more from Adriane Fugh-Berman.


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References

1. National Academy of Sciences (NAS) (2005). BEIR VII: Health Risks from Exposure to Low Levels of Ionizing Radiation. National Academies Press: Washington DC. Available from http://www.nap.edu/catalogor 800-624-6242.

2. Martin DR, Semelka RC (2006). Health effects of ionising radiation from diagnostic CT. Lancet. May 27;367(9524):1712-4.

3. Katz SI, Saluja S, Brink JA, et al. (2006) Radiation dose associated with unenhanced CT for suspected renal colic: impact of repetitive studies. AJR Am J Roentgenol. Apr;186(4):1120-4.

4. Parker MS, Hui FK, Camacho MA, (2005). Female breast radiation exposure during CT pulmonary angiography. AJR Am J Roentgenol. Nov;185(5):1228-33.

5. Brenner DJ, Elliston CD (2004).  Estimated radiation risks potentially associated with full-body CT screening. Radiology. Sep;232(3):735-8. Epub 2004 Jul 23.

6. Illes J, Fan E, Koenig BA, et al. (2003). Self-referred whole-body CT imaging: current implications for health care consumers. Radiology. Aug;228(2):346-51.

7. Lee CI, Haims AH, Monico EP, Brink JA, Forman HP. Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiology 2004;231:393-398.