Computed tomography (CT) scans may account for 5% of all cancers annually, according to a new study out of UC San Francisco that cautions against overusing and overdosing CTs. For children, the greatest risk comes from scans of the head.
The danger is greatest for infants, followed by children and adolescents. But adults are also at risk, since they are the most likely to get scans. In the U.S., nearly 103 000 cancers are predicted to result from the 93 million CT scans that were performed in 2023 alone. This is 3 to 4 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 UCSF radiologist and professor of epidemiology and biostatistics and obstetrics, gynaecology and reproductive sciences.
“Given the large volume of CT use in the United States, many cancers could occur in the future if current practices don’t change,” said Smith-Bindman.
“Our estimates put CT on par with other significant risk factors, such as alcohol consumption and excess body weight,” she said. “Reducing the number of scans and reducing doses per scan would save lives.”
Benefits and potential dangers
CT is both indispensable and widely used to detect tumours and diagnose many illnesses. Since 2007, the number of annual CT exams has surged by 30% in the U.S. But the ionising radiation dose from CT is a known cancer risk.
To assess the public health impact of current CT use, the study estimates the total number of lifetime cancers associated with radiation exposure in relation to the number and type of CT scans performed in 2023.
“Our approach used more accurate and individualised CT dose and utilisation data than prior studies, allowing us to produce more precise estimates of the number of radiation-induced cancers,” said co-author Diana Miglioretti, PhD, a breast cancer researcher and division chief of biostatistics at UC Davis. “These updated estimates suggest the excess risks – particularly among the youngest children – are higher than previously recognised.”
Researchers analysed 93 million exams from 61.5 million patients in the U.S. The number of scans increased with age, peaking in adults between 60 to 69 years old. Children accounted for 4.2% of the scans. The researchers excluded testing in the last year of a patient’s life because it was unlikely to lead to cancer.
Future cancers from radiation exposure
Adults 50 to 59 had the highest number of projected cancers: 10 400 cases for women, 9300 for men. The most common adult cancers were lung, colon, leukaemia, bladder and breast. 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, while in children they came from CTs of the head. Projected cancer risks were highest among those who underwent CT when they were under 1 year old. They were 10 times more likely to get cancer compared to 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 by getting fewer of these scans or by getting lower dose scans.
“There is currently unacceptable variation in the doses used for CT, with some patients receiving excessive doses,” Smith-Bindman said.
Co-author Malini Mahendra, MD, a UCSF assistant professor of Pediatric Critical Care, said it was important that families understand the risk of developing cancer from paediatric scans.
“Few patients and their families are counselled 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.”
