Increased cumulative exposure to radiation from computed tomography (CT) exams led to elevated risks for developing gliomas and other forms of brain cancer in children and young adults, according to the findings of a large multinational study of data from over 650,000 patients.
In the study, recently published in the Lancet Oncology, researchers reviewed pooled data from nine European countries and a total of 658,752 patients. All study participants had at least one CT exam prior to the age of 22 with no prior cancer or benign brain tumor, according to the study. Examining follow-up data at a median of 5.6 years, the study authors noted 165 brain cancers (including 121 gliomas). They also found that the overall mean cumulative brain radiation dose, lagged by five years, was 47.4 mGy for the study cohort in comparison to a mean cumulative brain radiation dose of 76.0 mGy for those with brain cancer.
“First results of (the study) after a median follow-up of 5.6 years show a strong dose-response relationship between the brain radiation dose and the relative risk of all brain cancers combined and glioma separately; a finding that remains consistent for doses substantially lower than 100 mGy,” wrote lead study author Michael Hauptmann, Ph.D., a professor of Biometry and Registry Research at the Brandenburg Medical School Theodor-Fontane in Neuruppin, Germany, and colleagues.
For head and neck CT exams, the researchers noted a “significant positive association” between the cumulative number of these procedures and elevated brain cancer risk. Employing linear dose-response modelling, the researchers found a 1.27 excess relative risk (ERR) per 100 mGy of brain radiation dosing for all brain cancers, a 1.1 ERR for gliomas and a 2.13 ERR for brain cancers excluding gliomas, according to the study.
Hauptmann and colleagues acknowledged that the risk estimates in the study translate to one out of 10,000 children experiencing a radiation-induced brain cancer five to 15 years after a head CT exam. However, the researchers also emphasized appropriate caution, pointing out annual estimates of pediatric head CT exams surpassing one million in the European Union and five million in the United States.
“These figures emphasize the need to adhere to the basic radiological protection principles in medicine, namely justification (procedures are appropriate and comply with guidelines) and optimization (doses are as low as reasonably achievable),” added Hauptmann and colleagues.
Study limitations included the potential for confounding indications with the study authors noting the inclusion of studies with some patients having congenital syndromes that may be predisposing factors for brain tumor development. However, Hauptmann and colleagues noted that exclusion of those patients and adjustments for those conditions saw no significant effect on the assessment of ERR.
The study authors also noted a lack of information on other imaging, such as nuclear medicine studies and X-rays, that may have been performed in the study population. However, they suggested the contribution of radiation dosing from these exams “is probably minor” in comparison to higher frequencies and dosing seen with pediatric head CT exams.