What Your Doctors Don’t Know Can Hurt You

Is your physician increasing your risk for cancer?

Can CT scans increase cancer risk?

Photograph by Thinkstock.

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?

Neither doctors nor patients like uncertainty, and CT scanners and other imaging modalities are not only widely accessible but provide beautiful and precise images. Doctors worry about being sued if something turns up on some later CT scan, so they order one now, just in case. Also, some doctors own their own CT scanners, making a pretty penny with each scan. And as doctors’ physical examination skills wane, there’s a greater reliance on medical imaging. Even more reasons: CT scans often get repeated when a patient goes to one hospital because it saves doctors the hassle of communicating with another hospital’s medical records department. And it’s not only doctors: Patients are eager to get the newest high-tech imaging (thanks to direct-to-consumer marketing), and since medical insurance frequently covers these scans, neither party needs to worry about the financial consequences of ordering a test that’s being done for less-than-compelling reasons.

There are many well-meaning doctors who believe they’re doing the right thing by ordering unnecessary scans. I remember one woman, years ago, who’d been suffering from severe headaches for two months and was convinced she had a brain tumor. I was sure she didn’t—her exam was normal and the pattern of headaches corresponded to the increasing stress in her life. Ordering a CT scan didn’t make sense, although she desperately wanted one. But her obsession with brain cancer was making her sick—she’d missed many days of work because of overwhelming anxiety. So one day I relented. I figured that putting her mind at ease would outweigh any risks from radiation and the cost of the scan. The CT scan was negative, her headaches disappeared, she went back to work, and the story seemed to have a happy ending. In retrospect, I don’t think it was worth exposing her to radiation and possibly—and ironically—increasing her risk for cancer. (Another study out last month found that children under 15 who had two or three head CT scans had three times the risk of brain cancer; the overall risk was very small, but it was still a risk.)

A single CT scan can expose the body to about the same amount of radiation as 100 X-rays, and in some situations, up to 400. (See Table 3 in this study for a comparison of radiation doses of various imaging tests.) But it’s not like eating two slices of cheesecake and going for a long run the next day to burn off the calories: Radiation exposure from medical imaging is likely cumulative. According to Dr. Howard Forman, professor of diagnostic radiology at the Yale School of Public Health and a practicing emergency and trauma radiologist, the damage adds up: “It’s like cigarette smoking: More is worse, but no matter how few or many cigarettes you smoke, it’s harmful.” 

The good news is that doctors and hospitals are starting to pay closer attention. Dr. Marilyn Goske, a professor of pediatric radiology at Cincinnati Children’s Hospital Medical Center and chairwoman of the Image Gently campaign, put it this way: “Look at the American car—it used to be a Cadillac with the big fins, and you didn’t pay attention to gas mileage. Now consumers are gas conscious. This is what’s happening in the CT world with increased emphasis on lowering radiation dose when possible.” In California, as of July 1, the dose of every CT scan must be documented in an electronic medical record. Forman offered a suggestion for the next step: a simply but strongly worded document that would be automatically generated every time a CT scan is ordered. “This patient has had four CT scans, each equal to x-number chest X-rays; we don’t know the definitive risk, but we know that patients with x times this exposure in Japan [after the atomic bombs] developed cancers.” At Southern New Hampshire Medical Center, Dr. Steven Birnbaum has created a sensible program to flag any patient under 40 who has had more than five  CT scans for benign diagnoses. The message to doctors is to think about whether the next CT scan is truly necessary and to discuss the increased risk with the patient.

In the world of pediatrics, the numbers are already improving. One study of CT use in pediatric emergency rooms found that the number of CT scans in kids fell between 2008 and 2010. And there’s more research ahead: In response to the Institute of Medicine article, Dr. Eric Winer, chief scientific adviser and chair of the scientific advisory board for Susan G. Komen for the Cure, told me that his foundation is funding studies looking at how to minimize risks from ionizing radiation from imaging studies.

And what’s most important is that there is mounting pressure for doctors to justify the CT scans they order—not only to the radiologist who will perform and interpret the test, but to the patient. Websites of public education campaigns like Image Gently and Ultrasound First provide information to patients and health care professionals about the importance of “child-sizing” radiation doses, since children are much more vulnerable to effects from ionizing radiation (and have more years ahead of them to potentially develop cancers triggered by those very scans intended to help). There’s also the Image Wisely campaign, part of the broader Choosing Wisely campaign, which provides evidence-based recommendations for common scenarios. Many, not surprisingly, have to do with CT scan overuse.

Perhaps the simplest ways to protect ourselves and our children from the risks of unnecessary CT scans (and from appropriate but too-highly dosed CT scans) are these: Keep track of your imaging tests and share this list with any doctor recommending an imaging study  (yes, there are apps for this), and don’t be too polite. The next time a doctor recommends a CT scan or any other imaging test, you shouldn’t assume it’s the only option. Ask if the result will change the treatment and whether there’s a safer way to get the necessary information. There’s a good chance your doctor hasn’t thought about it.

Correction, Aug. 2, 2012: This article originally stated that a researcher estimated that 6 percent of breast cancers would be caused by CT scans in a single year in the United States. The researcher actually estimated that of the total number of cancers caused by CT scans in a single year in the United States, 6 percent of them would be breast cancers.