CT Scan During Childhood Raises Risk for Brain Cancer After 5 Years

A significant dose-response relationship has been observed between computed tomography (CT)–related radiation exposure and brain cancer among children and young adults, according to the findings of a cohort study published in The Lancet Oncology.

Researchers sought to quantify the risk for brain cancer associated with CT scans in children and young adults. Data from 9 European countries (ie, Belgium, Denmark, France, Germany, the Netherlands, Norway, Spain, Sweden, and the United Kingdom) were pooled for the cohort study. All of the eligible participants had undergone ≥1 CT examination before age 22 years that had been documented between 1977 and 2014, had no prior diagnosis of cancer or a benign brain tumor, and were alive and free of cancer for ≥5 years following their initial CT scan. Participants were identified through the Radiology Information System in 276 different hospitals and were then linked with national or regional cancer registries.

The eligible cases comprised patients with brain cancer according to the World Health Organization International Classification of Diseases for Oncology. Analysis of gliomas was performed separately from that of all other brain cancers.

The outcome of the study was the first reported diagnosis of brain cancer and gliomas separately following an exclusion period of 5 years after the initial electronically recorded CT examination. The 5-year exclusion period was selected to prevent reverse causality (ie, CT scans that were administered because of present, but undiagnosed, malignancies at baseline).

A total of 948,174 individuals with ≥1 CT scan who were alive and cancer-free for
≥1 year following their initial CT examination were identified. Among these individuals, 69% (658,752 of 948,174) of them were eligible for the study. Among these participants, 56% were male and 44% were female. Over a median follow-up of
5.6 years (range, 2.4 to 10.1 years), 165 brain cancers were reported, of which 121 were gliomas.

The researchers found that the mean cumulative brain dose, which lagged by
5 years, was 47.4±60.9 milligray (mGy) among all individuals and 76.0±100.1 mGy among those with brain cancer. A significant linear dose-response relationship was reported for all brain cancers (excess relative risk [ERR] per 100 mGy, 1.27; 95% CI, 0.51-2.69), as well as for gliomas separately (ERR per 100 mGy, 1.11; 95% CI, 0.36-2.59). The study results were robust when the initiation of follow-up was delayed beyond 5 years, as well as when the participants with possible previously unreported cancers were excluded from the study.

A possible limitation of the study is reverse causation. All of the study participants had either suspected or real medical problems for which a CT examination had been indicated. These issues could, in theory, be considered early symptoms of a brain cancer that was subsequently diagnosed. An additional potential limitation is confounding by indication (ie, the CT scan is associated with an underlying condition that is related to an increased risk for brain cancer).

The researchers concluded, “The observed significant dose-response relationship between CT-related radiation exposure and brain cancer … with individual dose evaluation emphasises careful justification of pediatric CTs and use of doses as low as reasonably possible.”

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.