CT scans are significantly linked to an increased risk of blood cancers in young people, a major multinational study has found.

Analysis of data from nearly 1 million people under 22 who underwent at least one CT scan found a strong and clear link between exposure to the scans’ radiation and blood cancers, according to findings published Nov. 9 in the journal Nature Medicine.

Accumulated radiation doses to the bone marrow of 100 milligrays triples the risk of developing a blood cancer, researchers found.

Given that, a single CT scan – with an average dose of 8 milligrays – appears to increase the risk of blood cancer in children by about 16%, the researchers concluded.

“In terms of absolute risk, this means that, for every 10,000 children who have a CT scan, we can expect to see about 1-2 cases of cancer in the 12 years following the examination,” said lead researcher Magda Bosch de Basea, who did the study as a postdoctoral research fellow with the Barcelona Institute for Global Health (ISGlobal) in Spain.

For the study, researchers from nine European countries — Belgium, Denmark, France, Germany, Netherlands, Norway, Spain, Sweden and the U.K. — pooled resources to explore the risk of CT scans on children.

The extensive use of CT scanning in recent decades has led to concerns about the potential cancer risks associated with the radiation exposure involved, particularly in young patients, researchers said in background notes.

In the United States, about 5 to 9 million CT scans are performed annually on children, according to the National Cancer Institute. More than 1 million children in Europe undergo CT scans every year, the researchers said in an ISGlobal news release. 

“Although CT scans comprise up to about 12% of diagnostic radiological procedures in large U.S. hospitals, it is estimated that they account for approximately 49% of the U.S. population's collective radiation dose from all medical X-ray examinations,” the National Cancer Institute says on its website. “CT is the largest contributor to medical radiation exposure among the U.S. population.”

Children are much more sensitive to radiation than adults, are more likely to develop the health effects of radiation damage after receiving a scan at a young age, and might receive a higher radiation dose than necessary if doctors don’t adjust CT settings to account for their smaller size.

“The exposure associated with CT scans is considered low, but it is still higher than for other diagnostic procedures,” said Elisabeth Cardis, head of the Radiation Group at ISGlobal.

“Implementing this large, multinational study was challenging – it involved extracting data from radiology records of 276 hospitals and linking them to population-based registries in nine countries, all while maintaining the confidentiality of the individuals’ data,” Cardis added.

Researchers tracked individuals’ health for nearly eight years, on average, although they were able to monitor cancer incidence in some for more than 20 years after their first CT scan.

Although radiation doses from CT scans have decreased substantially in recent years, researchers said these findings underline the need to be careful with its use in young patients.

“The procedure must be properly justified — taking into account possible alternatives — and optimized to ensure that doses are kept as low as possible while maintaining good image quality for the diagnosis,” Cardis said.