At current use and radiation dose levels, computed tomography (CT) scans may eventually account for 5% of all cancers annually, according to a recent modeling study published by Smith-Bindman et al in JAMA Internal Medicine. The danger is greatest for infants, followed by children and adolescents—but adults are also at risk, since they are the most likely to have these scans.
Nearly 103,000 cancers are predicted to result from the 93 million CT scans that were performed in 2023 alone. This is three to four times more than previous assessments, the authors said.
“CT can save lives, but its potential harms are often overlooked,” said first author Rebecca Smith-Bindman, MD, a radiologist at the University of California, San Francisco (UCSF), as well as Professor of Epidemiology and Biostatistics and Obstetrics, Gynecology, and Reproductive Sciences; a member of the Philip R. Lee Institute for Health Policy Studies; and Director of the Radiology Outcomes Research Lab.
“Given the large volume of CT use in the United States, many cancers could occur in the future if current practices don’t change,” she added. “Our estimates put CT [exposure] on par with other significant risk factors, such as alcohol consumption and excess body weight. Reducing the number of scans and reducing doses per scan would save lives.”
Benefits and Potential Dangers of CT
CT imaging is both indispensable and widely used to detect tumors and diagnose many illnesses. Since 2007, the number of annual CT exams has surged by 30% in the United States. However, CT scans expose patients to ionizing radiation, and it’s long been known that the technology carries a higher risk of cancer.
To assess the public health impact of current CT use, investigators estimated the total number of lifetime cancers associated with radiation exposure in relation to the number and type of CT scans performed in 2023. They analyzed 93 million exams from 61.5 million patients in the United States. The number of scans increased with age, peaking in adults between the ages of 60 and 69. Children accounted for 4.2% of the scans. The researchers excluded tests in the patient’s last year of life, because these exposures were unlikely to lead to cancer.
Future Cancers From Radiation Exposure
Approximately 103,000 radiation-induced cancers were projected to result from these scans. Adults aged 50 to 59 had the highest number of projected cancers: 10,400 cases in women and 9,300 in men. The model also found that the CT scans performed in 2.5 million children would result in 9,700 cancers.
The most commonly projected adult cancers were lung, colon, bladder, and breast cancers as well as leukemia; the most frequently projected cancers in children were thyroid, lung, and breast.
The largest number of cancers in adults would come from CTs of the abdomen and pelvis, whereas in children, they would result from CTs of the head, the authors explained. Projected cancer risks were highest among those who underwent CT when they were younger than age 1—these individuals were 10 times more likely to develop cancer than others in the study.
The researchers said some CT scans are unlikely to help patients and are overused, such as those for upper respiratory infections or for headaches without concerning signs or symptoms. They said patients could lower their risk of cancer by having fewer or lower-dose scans.
“There is currently unacceptable variation in the doses used for CT, with some patients receiving excessive doses,” Dr. Smith-Bindman said.
Coauthor Malini Mahendra, MD, Assistant Professor of Pediatric Critical Care at UCSF, said it was important that families understand the risk of developing cancer from pediatric scans. “Few patients and their families are counseled about the risk associated with CT examinations,” she said. “We hope our study’s findings will help clinicians better quantify and communicate these cancer risks, allowing for more informed conversations when weighing the benefits and risks of CT exams.”
Disclosure: The research was supported in part by awards from the National Cancer Institute and the Patient-Centered Outcomes Research Institute. For full disclosures of the study authors, visit jamanetwork.com.
