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This story has been updated with outside expert commentaries and additional context. 

TOPLINE:

CT examinations performed on 62 million patients in the United States during 2023 are projected to result in approximately 103,000 future cancer cases, according to a recent modeling study. The researchers estimate that CT "could be responsible for approximately 5% of cancers diagnosed each year." 

However, experts commenting on the modelling study in a roundup from the Science Media Centre (SMC) put this additional cancer risk into greater context.

"Importantly, this study models estimated cancer risk from radiation exposure. It does not show a direct causal link between specific CT scans and individual cancer cases," explained Doreen Lau, a lecturer in Inflammation, Ageing, and Cancer Biology at Brunel University of London. "These are projections based on population-level data and assumptions about radiation risk, not observed cancer rates." 

And an alternative way of viewing the projected numbers, according to Giles Roditi, would be that "although the figure of 100,000 cancers is alarming, this is only a small additional risk over and above an individual’s lifetime risk of developing cancer." In other words, this is "a risk rising from about 50% to 52.5%," wrote Roditi, consultant cardiovascular radiologist and honorary clinical associate professor of radiology, University of Glasgow, Scotland.

METHODOLOGY:

• Approximately 93 million CT examinations are performed on 62 million patients annually in the United States. CT exams help diagnose cancer but also expose patients to ionizing radiation that can increase cancer risk.
• An analysis from 2009 analysis estimated that about 29,000 future cancers would result from routine CT use in the US in 2007, but since 2007, the number of CT examinations performed annually has increased by more than 30%.
• To update the projected lifetime cancer incidence associated with CT use, researchers performed a risk model analysis using data from 121,212 CT examinations collected between January 2018 and December 2020 from 143 hospitals and outpatient facilities across 22 healthcare organizations in the US.
• Researchers estimated organ doses for 18 organs through Monte Carlo radiation transport simulations.
• Analysis included projecting future lifetime radiation-induced cancer risk using the National Cancer Institute’s Radiation Risk Assessment Tool version 4.3.1.

TAKEAWAY:

• CT use in the US in 2023 was estimated to result in 102,700 projected lifetime cancers — 93,000 in adults and 9700 in children. The most common cancers projected to occur in adults included lung cancer, colon cancer, leukemia, and bladder cancer, and those in children included thyroid, lung, and breast.
• Abdomen and pelvis CT examinations in adults contributed the largest proportion of projected cancers (37,500 cases), representing 37% of all cases, while head CTs contributed to the largest number of projected cancers in children (53%).
• Cancer risk per CT examination was highest in children aged under 1 year, with girls showing 20 cancers per 1000 examinations compared with 2 per 1000 in girls aged 15-17 years.
• Although children had a higher risk per exam, adults had the highest risk overall, given greater use of CT in older patients. For instance, the modeling projection showed that CT use in adults aged 50 to 59 years was associated with the highest number of projected cancers (10,400 in females and 9300 in males).

IN PRACTICE:

“If current practices persist, CT-associated cancer could eventually account for 5% of all new cancer diagnoses annually," the authors concluded. "This would place CT on par with other significant risk factors, such as alcohol consumption (5.4%) and excess body weight (7.6%)."

While praising the high quality of the study, several outside experts commenting in a SMC roundup put this risk in less alarming terms. 

"This is a well-conducted modelling study using robust data from US hospitals and established methods for estimating cancer risk from radiation exposure," said Lau. "It provides a timely reminder that while CT scans are often life-saving and essential for diagnosis, they do come with a small but real potential risk of contributing to cancer over a lifetime, especially when used repeatedly, in younger patients, or when not clinically necessary." 

But, Lau explained, "the findings don’t mean that people should avoid CT scans when recommended by a doctor. In most cases, the benefit of detecting or ruling out serious illness far outweighs the very small risk of harm." What this research highlights, she continued "is the need to minimize unnecessary imaging and use the lowest dose possible, particularly in settings where CT usage is high."

Stephen Duffy agreed, noting that the authors' estimate that just over 100,000 cancers are predicted to occur as a result of radiation from these CT examinations really "amounts to around a 0.1% increase in cancer risk over the patient's lifetime per CT examination." 

"When we consider that the lifetime risk of cancer in the general population is around 50%, the additional risk is small," said Duffy, Emeritus professor of cancer screening, Centre for Cancer Screening, Prevention and Early Diagnosis, Queen Mary University of London. "It seems to me that the likely benefit in diagnosis and subsequent treatment of disease outweighs the very small increase in cancer risk." 

SOURCE:

The study was led by Rebecca Smith-Bindman, MD, Department of Epidemiology and Biostatistics, University of California, San Francisco. It was published online on April 14 in JAMA Internal Medicine.

LIMITATIONS: 

According to the authors, the risk model parameters are primarily based on Japanese atomic bomb survivor outcomes, raising questions about the transferability of radiation risks from the mid-20th century Japanese population to the current US population. The calculations factored in average life expectancies, potentially overestimating future cancer risk for patients who undergo CT and have shorter life expectancy due to underlying illness. Additionally, while the CT categorization algorithm was 90% accurate compared with expert review, some examinations may have been miscategorized. 

DISCLOSURES:

The research was supported by awards from the National Cancer Institute, the Patient-Centered Outcomes Research Institute, and residual class settlement funds from a legal case. Smith-Bindman disclosed being a co-founder of Alara Imaging, Inc., a company focused on improving clinical and operational aspects of health systems, including radiation dose and image quality reporting for CT as part of payer-led quality programs. Additional disclosures are noted in the original article. Duffy and Lau reported no financial or conflicts of interest related to this study. Roditi is a past president of the British Society of Cardiovascular Imaging/Cardiovascular CT and of the Society of Magnetic Resonance Angiography as well as a member of the SCOT-HEART investigators. 

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.