Computed tomography (CT) scans may be one of the greatest innovations in modern medicine — fast, detailed and essential for diagnosing everything from traumatic injuries to cancer. But a new study published in JAMA Internal Medicine has reignited a complex and sometimes controversial debate on CT cancer risk: Is widespread use of CT quietly fueling a future wave of cancers?

The study, led by researchers at the University of California, San Francisco, projects that the 93 million CT scans performed in the U.S. in 2023 may eventually lead to 103,000 additional cancer cases. If true, that would make CT imaging responsible for roughly 5% of all new cancers diagnosed annually — on par with alcohol and just behind obesity and ultra processed food​.

According to the study, the risks don’t come from a single scan, but from cumulative exposure to ionizing radiation — a known carcinogen. This is of particular concern in individuals who receive many CTs. For example, in patients with Crohn’s disease or with kidney stones where the frequent scans can be pivotal in appropriately treating acute flares of these conditions. Additionally, the sheer volume of imaging exposure amplifies the potential population-level harm.

But not everyone agrees with the alarm bells.

Radiologists Pushback Arguing The Study Is Flawed Because CT Cancer Risk Is Theoretical

The American College of Radiology (ACR) issued a pointed critique of the study. They called its conclusions “theoretical” emphasizing that there is no direct, real-world evidence linking CT scans in adults — even multiple scans — to cancer in humans.

Patients "…should not forgo necessary, life-saving medical imaging,” the ACR urged, also emphasizing that newer CT technologies and protocols have significantly reduced radiation doses per scan​. Today’s scans often use 30–50% less radiation than a decade ago.

The ACR is correct. CT imaging has contributed to major public health gains, including lower cancer mortality, fewer exploratory surgeries, and shorter hospital stays. CTs are also deeply embedded in clinical workflows. Physicians rely on their speed and accuracy. Patients expect them.

A central, yet overlooked piece in the “CTs cause cancer” narrative comes from a large 2009 study published in the Journal of the American College of Radiology. The counter narrative is that fewer imaging tests – including CTs – may increase in-hospital mortality. This argues for a more liberal approach to imaging, on average.

The researchers analyzed over 1.1 million inpatient admissions across 102 U.S. hospitals to explore whether hospitals that used more imaging had better outcomes. Hospitals where patients were more likely to receive imaging—including CT, MRI, ultrasound, or X-rays—had significantly lower in-hospital mortality, even after adjusting for patient and hospital characteristics​. The association was strongest for ultrasound and CT.

Interestingly, the number of scans per patient wasn’t as strongly correlated with improved outcomes as simply whether imaging was used at all. This suggests that the first scan may be the most valuable, in particular the one that is often done in busy emergency departments. Additional imaging after that may yield diminishing returns.

The CT Cancer Risk Concerns Should Focus On Its Overuse

Yet at the same time, ionizing radiation – core to CT technology – is still a carcinogen, which is of concern. Therefore, the aggregate cancer risk from all this radiation may be a significant issue multiplied across so many tens of millions of scans.

The JAMA study focused on specific types of tests as the theoretical cancer culprits. In particular, CT imaging of the abdomen and pelvis was their single largest contributor to projected cancer cases, followed by chest and spine scans. This is because those scans use more radiation than CTs of, for example, the brain. Additionally, these scans irradiate the lungs, breasts, thyroid, and digestive system which are more sensitive to the effects of ionizing radiation.

Of particular concern are the risks of CT in children, particularly those under age 1, who have the highest theoretical per-scan risk due to more vulnerable tissues and longer post-exposure lifespans​. Additionally, despite the lack of direct causal evidence in adults, studies in pediatric populations have shown increased rates of leukemia and brain tumors following CT exposure.

How Physicians and Healthsystems Can Address CT Cancer Risk

Given the life-saving nature of CTs and their central role in healthcare delivery, disrupting their use dramatically would certainly lead to poorer outcomes. However, there are several options to reduce their potential harm without compromising care:

  • Promote the adoption clinical decision support tools that flag low-value imaging at the point of care. For example, there are validated decision rules that can safely guide the reduction of brain CT imaging in both adults and children with minor head injury.
  • Reduce use of multiphase CT scans, which involve multiple exposures per session, as these additional images often provide little added value in improving diagnosis.
  • Encourage alternative imaging, such as the use of ultrasound or magnetic resonance imaging (MRI) which do not involve ionizing radiation, especially in younger patients and in patients who require follow-up imaging.
  • Standardize radiation protocols to reduce unnecessary variation in dose between hospitals and imaging centers. This can help avoid the exposure to unnecessarily high doses of ionizing radiation.
  • Educate clinicians and patients alike about the risks of cumulative exposure — and the importance of judicious imaging.

Studies have also shown that physicians’ imaging behaviors are malleable. Cultural change is possible — particularly if paired with tools, training, and transparency.

A Call For Balancing CTs Benefits V. Potential CT Cancer Risk

Ultimately, CT scans are an indispensable tool. But that doesn’t mean every scan is necessary — or harmless. This latest research, along with the ACR’s response, signals a need for honest reflection, not alarmism.

It is important to resist the binary framing of "CT is good" vs. "CT is dangerous" in the CT cancer risk v. benefit discussion. The truth is more complex — and more actionable. As to whether the CTs are really a leading cause of cancer – the jury is still out on that given the theoretical but potentially concerning risks of ionizing radiation. The challenge ahead is to preserve the life-saving power of imaging while minimizing the silent harms that may emerge years later.