rewrite this title Do CT Scans Cause Cancer? Study Finds Imaging May Fuel 1 in 20 U.S. Cases Each Year

Computed tomography (CT) scans are a pivotal part of U.S. medical care. These sophisticated X-rays give doctors detailed views of what’s happening inside the body, allowing them to make diagnoses, monitor treatment progress, locate injuries or tumors, and more. 

But the technology doesn’t only detect health problems. In some cases, recent research suggests, it may actually cause them. In the future, CT scanning may account for roughly 5% of cancers diagnosed annually in the U.S., according to a study recently published in JAMA Internal Medicine. 

The study is not the first to suggest that CT scans may contribute to cancer risk. The technology exposes people to ionizing radiation, which doctors and researchers have long known can cause DNA damage.

“Some of that damage can be repaired,” explained the new study’s lead author, Rebecca Smith-Bindman, MD, a professor of epidemiology and biostatistics at the University of California, San Francisco School of Medicine and co-founder of a company that aims to improve radiology quality in the U.S. “But some of it persists, and that’s what leads to known cancer.” 

Despite that possibility, “the potential harms of CT scanning are often overlooked,” Smith-Bindman told Health. Her team set out to correct that situation by quantifying the number of cancers that stem from CT imaging.

Past research has also tried to measure just how often CT scans lead to cancer cases, but prior estimates have become outdated as the technology explodes in popularity. CT scans are used about 30% more often today than in 2007, according to the new study, driven by factors like advancing technology, an aging population, and changing healthcare practices.

“It’s often easier for a physician to order a test than it is to spend time with a patient figuring out what’s going on,” Smith-Bindman said, adding that patients sometimes ask for unnecessary tests, too.

To reach a more current estimate, Smith-Bindman’s team focused on the approximately 93 million CT scans performed on 61.5 million Americans in 2023 alone. Using various data sources, they estimated the ages and sexes of those patients, the types of scans they got, and the doses of radiation to which they were likely exposed. Then, they used a risk calculator created by the National Cancer Institute to estimate how many future cancers would likely result from those tests. 

When all was said and done, they concluded that the scans would eventually cause around 103,000 cancers, affecting organs including the lungs, colon, bladder, breast, and more. If current imaging practices and cancer rates hold steady, CT scans could eventually be responsible for about 5% of annual diagnoses, the researchers estimated.

“For something to account for 5% of all cancers is pretty significant,” Smith-Bindman said. Well-known cancer risk factors, like obesity and alcohol consumption, are responsible for roughly as many diagnoses, she noted.

That said, it’s important to remember that the numbers in the study are estimates based on mathematical models, not results from actual patients, Patricia Nguyen, MD, an associate professor of medicine at Stanford University who was not involved in the new study but has previously researched the effects of CT scans, told Health. It’s “a bit of a reach” to conclude that any one risk factor causes a specific percentage of cancers, especially based on a modeling study, Nguyen said. 

She echoed points raised in a statement from the American College of Radiology, which urged Americans not to “forgo necessary, life-saving medical imaging.”

Nonetheless, it’s true that CT scans—like most medical procedures—are not totally risk-free, Nguyen said. Patients and their doctors must work together to decide when the benefits outweigh the drawbacks, and vice versa.

There are many times when CT scanning is clearly worth doing, said Max Wintermark, MD, chair of the neuroradiology department at the University of Texas MD Anderson Cancer Center, who was not involved in the new research. If someone is involved in a traumatic accident, for example, CT scanning can quickly “detect life-threatening injuries that otherwise couldn’t be detected,” allowing them to be properly treated, Wintermark told Health.

The technology can also be crucial for monitoring certain diseases and guiding surgeries, Nguyen added.

But there are instances when patients may be able to skip the test or opt for a method that doesn’t expose them to radiation, such as magnetic resonance imaging (MRI) or ultrasound. 

“The patient needs to be their own advocate,” Nguyen said, recommending that people ask their doctors why a CT is recommended, what they hope to learn from it, and how its results may guide treatment decisions. If the test won’t change treatment, or if there’s a radiation-free alternative available, it may make sense to go without the CT. 

“One way to reduce the risk of cancer is to reduce unnecessary tests,” Smith-Bindman agreed. “The second way is to reduce the radiation doses for each scan.” She recommended that patients who need a CT ask their care team to use the lowest effective dose possible.

It’s especially important for parents to ask those questions on behalf of their children, Smith-Bindman said. Her study estimated that the younger someone is, the higher their cancer risk following a CT scan. Babies scanned before their first birthdays were thought to be 10 times more likely to get cancer than older people in the study—perhaps because their bodies are still developing and they have decades of life ahead, giving cancer more time to develop, Wintermark said. 

Adults, however, undergo far more scans than children and babies do, so they accounted for a much larger portion of the estimated cancer cases—about 93,000 of the 103,000.

While the study’s conclusions may be frightening, patients of all ages should be reassured that “behind each CT scanner, there’s a team of experts,” Wintermark said. Radiologists are physicians, and they are trained to review a patient’s unique characteristics and medical records to make sure risks and benefits are balanced as well as possible, he said.

“We take the results of this study, and all the other studies that have been published around this topic, very, very seriously,” Wintermark said. “We really make every possible effort to minimize the risk and figure out if there’s an alternative test available.”