Higher risk of brain cancer after childhood CT exam

According to a cohort study of more than 650,000 children and young adults, there has been an increased risk of brain cancer associated with increased radiation dose to the brain from CT examinations.

The researchers observed a significant dose-response relationship such that for every 10,000 people who received a single head scan, approximately one patient developed brain cancer attributable to radiation exposure within 5 to 15 years of the scan, reported Michael Hauptmann, PhD, biostatistician at Brandenburg Medical School in Neuruppin, Germany, and his colleagues from the EPI-CT study.

“To put this finding into context, the number of pediatric CT scans per year over the past decade likely exceeds 1 million in the [European Union] and 5 million in the United States,” they reported in The Lancet Oncology.

“Only a small fraction of attributable brain cancers might be preventable (i.e., those with unnecessarily high doses on CT examinations or the presumably larger group with clinically unwarranted CT examinations),” Hauptmann and these partner’work. “Nevertheless, these figures underline the need to adhere to the basic principles of radiation protection in medicine, namely justification (procedures are appropriate and in accordance with recommendations) and optimization (doses are as low as reasonably achievable).

Indeed, the use of CT scans has already declined in recent years amid efforts to both substantiate and optimize such scans, according to Nobuyuki Hamada, PhD, a radiobiologist at Japan’s Central Industrial Research Institute. electric power in Tokyo, and Lydia Zablotska, MD, PhD, radiobiologist epidemiologist from the University of California, San Francisco.

“Such continued efforts, along with extensive epidemiological investigations, would be needed to minimize the risk of brain cancer after pediatric CT examination,” they wrote in an editorial accompanying the study.

In the EPI-CT study, Hauptmann and colleagues identified 978,174 people from nine European countries who had at least one CT scan before the age of 22 documented between 1977 and 2014.

For the purposes of this analysis, the researchers included 658,752 people who were alive and cancer-free (including free of known brain tumors of benign or unknown behavior) 5 years after their first CT exam and followed them for an additional median of 5.6 year.

Of the patients analyzed, 82% were under 30 at the end of follow-up, 56% were men and 73% had received at least one head or neck scan.

During follow-up, 165 cases of brain cancer were reported, of which 73% were gliomas.

With a 5-year lag, the mean cumulative brain dose was 47.4 mGy in all individuals and 76.0 mGy in people with brain cancer.

Hauptmann and colleagues estimated that each 100 mGy dose to the brain results in a 127% increased risk of brain cancer (95% CI 51-269), a 111% increased risk of glioma (95% CI 36-259) and a 213% increase in the risk of brain cancer. cancer risk excluding gliomas (95% CI 25-136).

The average brain dose by CT head or neck in 2012-2014, 38 mGy, was associated with an excess risk of brain cancer compared to a brain dose of 0 mGy (RR 1.5, 95% CI 1.2 -2.0).

The authors acknowledged several limitations to the observational study, including the possibility of reverse causation.

Although an exclusion period of 5 years after the first recorded CT examination was chosen to minimize the possibility that a person had pre-existing brain cancer, the authors acknowledged that the participants had actual or suspected medical problems for which a CT scan was indicated. So, they suggested, “these problems could, in theory, be the first symptoms of brain cancer subsequently diagnosed.”

They also said there may be some uncertainty regarding the dose estimates, as they were obtained retrospectively from a number of data sources. “Detailed technical information for dose estimation was particularly scarce during the years before 1990,” they noted.

Hamada and Zablotska added that longer follow-up would be needed to understand age trends, as the average age at the end of the present study was only 22 and it is only at 30. years on average that glioma population rates begin. increasing.