A couple of years ago, my doctor recommended a CT scan of my abdomen to follow up on a minor abnormality. Dutifully, I made the appointment, grimaced as I chugged a liter of the chalky contrast liquid, and lay still as the white machine clicked a couple hundred cross-sectional slices from the base of my lungs through my liver, kidneys, spleen, gallbladder, intestine, and uterus. I was told that everything looked fine, and, until I started working on this article, I’d almost forgotten about it. But looking back, I realize that no one—not my doctor, not the radiologist, not the tech—had told me how much radiation I’d be exposed to or suggested a different test. Even though I knew in the back of my mind (as every doctor does) that CT scans wallop us with a generous dose of radiation, my working assumption was that someone would have said something if there was something to say.
Of course, since I’m a doctor, “someone” includes me, and here’s the truth: I, like many doctors, do not discuss the radiation risks of CT scans with my patients often enough, if at all.
Despite much research and media attention, a good number of doctors and patients are still not getting it. Ionizing radiation can damage DNA and result in cancer-causing mutations; CT scans dole out plenty, likely increasing the risk for cancer. And, yes, we can do something about it.
Consider the latest bad news about imaging studies and breast cancer from the July Archives of Internal Medicine. The author, Dr. Rebecca Smith-Bindman, a professor of radiology at the University of California-San Francisco School of Medicine, spells out in no uncertain terms that medical imaging, particularly CT scanning, remains a major and often overlooked risk factor for breast cancer. The paper summarizes a 400-plus page 2011 Institute of Medicine report about environmental risk factors for breast cancer in response to a request by the Susan G. Komen Foundation. The goal was to identify risk factors that women could do something about. Those that didn’t make the cut? The suspects du jour, like industrial chemicals, pesticides, and other maligned substances such as bisphenol A. The two that did—combination estrogen-progestin hormone therapy and ionizing radiation from medical imaging—are only available with a doctor’s order.
After the Women’s Health Initiative, a 15-year study organized by the National Institutes of Health that focused on postmenopausal women, showed a link between combination hormone replacement and an increased risk of breast cancer in 2002, many women took things into their own hands. They stopped their hormones (the number of prescriptions for the two leading formulations of hormone replacement therapy fell 66 percent and 33 percent in the year after the study came out), and the breast cancer rate in women over 50 decreased (though there’s still some controversy about whether the drop in hormone use directly lowered the rate of breast cancer).
But cutting down on ionizing radiation from medical imaging is more complicated, in large part due to uninformed doctors. One study found that less than half of radiologists and only 9 percent of emergency-room doctors were aware that CT scans could increase the risk of cancer. While the risk-benefit discussion has become part and parcel of hormone replacement therapy prescribing, far fewer doctors are warning their patients about the potential risks from CT scans.
What makes this issue especially hard to sort out is that nobody can say with utter certainty whether a specific cancer evolved from a couple of CT scans many years earlier. But the predictions are worrisome. One researcher estimated that as many as 29,000 cancers, about 6 percent of which would be breast cancers, would develop as a result of the CT scans used in a single year in the United States.* Another researcher's calculations showed that one cancer might appear for every 270 middle-aged women who had CT coronary angiography, with the risk higher for younger women.
Meanwhile, the number of CT scans (and medical imaging tests in general) is rising: A recent Journal of the American Medical Association study found that the rate of CT-scan ordering in a group of HMOs increased by almost 20 percent between 1996 and 2010. A 2009 study of 1 million U.S. adults found that 70 percent had at least one medical imaging test in the three years of the study, with higher cumulative doses in women and older adults. The Archives of Internal Medicine study reported that the use of CT scans has risen almost fivefold in the last 20 years, that half of the 75 million CT scans each year in the United States are for women, and, disturbingly, that it’s estimated that at least 30 percent of all CT scans may be unnecessary.
So why are we administering so many of them?