Study suggests CT scans could cause 100,000 more cancer cases in U.S.

A large-scale study of CT scans performed in the United States has estimated that the widely used medical technology could lead to more than 100,000 cases of cancer in the lives of patients. The study, “Projected Lifetime Cancer Risks From Current Computed Tomography Imaging,” was published in the medical journal JAMA Internal Medicine by Dr. Rebecca Smith-Bindman, a professor of epidemiology and biostatistics at the University of California, San Francisco. She found that, in 2023, 61.5 million Americans underwent a total of 93 million CT exams — slightly more females (53 per cent) than males, and many more adults (95.8 per cent) than children. CT scans use ionizing radiation of the same type as standard X-rays, but in higher doses . A chest X-ray delivers about as much radiation as one receives naturally from the environment over 10 days, but a CT scan can deliver hundreds of times that much, equivalent to two years of background radiation. Smith-Bindman wrote: “Approximately 103 ,000 radiation-induced cancers were projected to result from these examinations.” The most common were lung cancer, colon cancer, leukemia and bladder cancer, while in female patients, breast cancer was the second most common. “These findings suggest that if current radiation dosing and utilization practices continue, CT-associated cancers could eventually account for 5% of all new cancer diagnoses annually.” Reached by phone, Smith-Bindman told the National Post that with “back of the napkin calculations,” those numbers could be roughly applied to Canada as well. In 2022, about 6.4 million CT scans were performed in Canada, which would translate to about 7,200 new cancer cases over the lives of those patients.

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One problem with the CT scan, she said, was its ubiquity. She noted a study done by a group called Choosing Wisely , which asked medical organizations to indicate tests that were used more than needed. “One of the tests that was identified by many medical societies that their members overused was CT scans,” she said. One example was routine use before surgery or to look for blood clots when none were suspected. “CT scans are a good way to look for blood clots, but it’s way over-utilized.” She added: “Part of the reason that there’s so much overuse is that the potential harm of medical imaging and of CT scanning in particular is not considered or assessed. There’s an optimistic view of medial imaging, that it provides useful information at no cost or harm to the patient. And that’s not true. Everything we do in health care comes with potential risk. CT scanning, just like everything else, has potential risks and potential benefits.” Smith-Bindman added that alternate imaging techniques can sometimes be used. “We know that ultrasound is a really good test for diagnosing kidney stones or children’s acute appendicitis and yet CT scanning is often used for the test when ultrasound would be just as good or better.” The radiation dose can also be modified so that it does not exceed certain thresholds, and is not higher than needed for a particular scan. Smith-Bindman suggested a organization called Know Your Dose to learn about all types of medical dosages. She was cautious about patients turning away from CT scans in every situation, however. “Sometimes CT scanning is the right test to provide the most accurate or rapid information. And in those settings patients should get the CT. But in many situations there are alternatives, and I encourage patients to have these conversations with their health care providers.” She also had some personal anecdotes on the use of CT. When her son was injured in a skiing accident, the ER doctor gave her the choice of running a CT for possible concussion but added that he didn’t think it was necessary. She declined. “But another setting, same son, fell out of a tree, hit his head, and we took him to the emergency department. They wanted a CT and we said: ‘Great, let’s get a CT.'” That one was clean. But hours later, the doctors suggested another CT “to make sure nothing had developed.” Her husband (also a doctor) suggested they just watch their son instead and make sure he was OK. “And the doctor said: ‘Oh you can do that instead.’ And we said: ‘Well that’s what we’re going to do instead. We don’t want a second CT.'”