CT scans — those marvels of modern imaging that can peer inside our bodies in seconds — may also be contributing to a slow-moving wave of cancer.

A new modeling study estimates that radiation from CT scans performed in the United States in 2023 could eventually cause more than 100,000 cases of cancer. That’s nearly 1 in every 20 new diagnoses — putting it on par with alcohol as a cancer risk factor. The authors say this should be a wake-up call.

“While CT scans are immensely beneficial… they do involve exposure to ionising radiation that has been shown to increase the risk of developing cancer,” said Professor Amy Berrington of the Institute of Cancer Research, London, who co-led the study.

“For the individual patient, this increased risk is small… but when millions of CT scans are being carried out across the population, these small risks do add up.”

The Benefits Are Real — But So Are the Risks

The numbers are staggering. Roughly 93 million CT scans were performed in the U.S. in 2023, across 62 million patients. Some of those patients were scanned multiple times. About 2.5 million of them were children.

By feeding that data into a radiation risk model — one originally developed to estimate cancer risk after exposure to atomic bomb blasts — the researchers projected that these scans could result in about 103,000 future cancers. That includes 9,700 cases in children.

The most common cancers expected from CT scans were those of the lung, colon, bladder, and breast, as well as leukemia. Adults receiving abdomen and chest scans accounted for the majority of projected cases. But the lifetime risk was proportionally higher in children, especially those under one year old. For young girls, brain and thyroid cancers were a particular concern.

Still, doctors stress that CT imaging is indispensable. But with one condition: only if you have a chronic illness such that the benefits outweigh the radiation risks.

“CT scanning is accurate, quick, well-tolerated, and relatively inexpensive,” noted the JAMA editorial accompanying the study. “Its success as an imaging modality is also what makes it so challenging to constrain.”

Dr. Cynthia McCollough, a CT imaging expert and past president of the American Association of Physicists in Medicine, echoed that balance: “Any risk from a CT scan of a sick patient is likely much less than the risk of the underlying disease.”

A Growing Dependence on CT Scans

The widespread use of CT technology is relatively new. In 1980, fewer than 3 million CT scans were performed annually in the United States. By 2007, that number had skyrocketed to 69 million. Today, it’s over 93 million—a more than 30 percent increase since 2009.

“CT is frequently lifesaving, yet its potential harms are often overlooked,” said Dr. Rebecca Smith-Bindman, a radiologist and epidemiologist at the University of California, San Francisco, and lead author of the study. “Even very small cancer risks will lead to a significant number of future cancers given the tremendous volume of CT use in the United States.”

Unlike older studies, which relied on broad assumptions, this analysis used detailed data from 143 hospitals and imaging centers across the country. The UCSF International CT Dose Registry helped researchers estimate actual radiation doses by body part, patient size, and device type — making this one of the most comprehensive models to date.

But it’s still a model, not a direct measurement. Proving a link between low-dose radiation and cancer risk remains difficult. Most evidence comes from high-dose events — atomic bombs or nuclear meltdowns. In Hiroshima, for instance, people who absorbed doses similar to three or more CT scans showed a small but measurable increase in lifetime cancer risk.

That uncertainty matters. “To empirically quantify lifetime risk would require decades-long follow-up studies of very large populations,” the authors admit.

Yet many experts argue that caution is warranted regardless.

“Estimated overall cancer risks from CT radiation doses are similarly high in Australian studies,” said Dr. Pradip Deb, a medical radiation specialist at RMIT University in Australia. “It is important to avoid unnecessary CT scans if radiation-free procedures can do the same job.”

What Can Be Done?

The researchers are not calling for a CT ban. That’s not the point at all. Rather, they’re urging more restraint.

“These future cancer risks can be reduced either by reducing the number of CT scans… or by reducing the doses per exam,” said Dr. Smith-Bindman. She points out that radiation doses vary widely between hospitals — and sometimes even between scans at the same facility.

The key, experts say, is ensuring that every scan is medically necessary, and that radiation doses are tailored to the patient’s size and needs. In the UK, strict regulations require radiologists to review scan requests before they’re approved. As a result, Britain has one of the lowest CT rates in the developed world — under 100 scans per 1,000 people, compared to more than 250 in the U.S.

Some private clinics, however, offer full-body CT scans to healthy people, touting them as peace-of-mind tools. The researchers warn against this practice.

“The risk of cancer outweighs any potential benefit from the whole-body scans offered by private clinics to healthy people,” Berrington said bluntly.

Consumer Reports flagged similar concerns back in 2015, estimating that up to one-third of CT scans may be unnecessary. That’s a lot of radiation with no clinical upside.

CT technology is not going away. Nor should it. But this study is a reminder that even our most powerful medical tools carry risks — especially when used without care.

“While we search for smarter, kinder treatments for cancer patients,” said Professor Kristian Helin, CEO of The Institute of Cancer Research, “we must also seek to understand how to prevent the disease.”

The findings appeared in the journal JAMA Internal Medicine.