Dear EarthTalk: Should I fear radiation exposure associated with medical scans such as CT scans, mammograms and the like?

— Shelly Johansen, Fairbanks, AK

The short answer is…maybe. Critics of the health care industry postulate that our society’s quickness to test for disease may in fact be causing more of it, especially in the case of medical scans. To wit, the radiation dose from a typical CT scan (short for computed tomography and commonly known as a “cat scan”) is 600 times more powerful than the average chest x-ray.

A 2007 study by Dr. Amy Berrington de González of the National Cancer Institute projected that the 72 million CT scans conducted yearly in the U.S. (not including scans conducted after a cancer diagnosis or performed at the end of life) will likely cause some 29,000 cancers resulting in 15,000 deaths two to three decades later. Scans of the abdomen, pelvis, chest and head were deemed most likely to cause cancer, and patients aged 35 to 54 were more likely to develop cancer as a result of CT scans than other age group.

Another study found that, among Americans who received CT scans, upwards of 20 percent had a false positive after one scan and 33 percent after two, meaning that such patients were getting huge doses of radiation without cause. And about seven percent of those patients underwent unnecessary invasive medical procedures following their misleading scans. CT scans are much more common today than in earlier decades, exacerbating the potential damage from false positives and excessive radiation exposure.

“Physicians and their patients cannot be complacent about the hazards of radiation or we risk creating a public-health time bomb,” says Dr. Rita Redberg, a cardiologist at University of California-San Francisco. “To avoid unnecessarily increasing cancer incidence in future years, every clinician must carefully assess the expected benefits of each CT scan and fully inform his or her patients of the known risks of radiation.”

CT scans are not the only concern. Mammograms are now routine for women over 40 years old. But some studies suggest that these types of screenings may cause more cancers than they prevent. Because of this, the federally funded U.S. Preventive Services Task Force now recommends that women not otherwise considered high risk for breast cancer wait until age 50 to begin getting mammograms — and then to get them every two years instead of annually. However, the American Cancer Society argues that such restraint would result in women dying unnecessarily from delaying screenings.

Women with a family history of breast cancer may be at greatest risk. Researchers from the University Medical Center Groningen in the Netherlands found that five or more x-rays — or any exposure to radiation — before the age of 20 for “high risk” women increased the likelihood of developing breast cancer later by a factor of two and a half.

Individuals should ask tough questions of their physicians to determine if and how much screening is absolutely necessary to look for suspected abnormalities. Our knowledge of the risks of radiation-based screenings will only help us to make more informed decisions about our health.

SEND YOUR ENVIRONMENTAL QUESTIONS TO: EarthTalk®, c/o E – The Environmental Magazine, P.O. Box 5098, Westport, CT 06881; earthtalk@emagazine.com. E is a nonprofit publication. Subscribe: www.emagazine.com/subscribe; Request a Free Trial Issue: www.emagazine.com/trial.