A large-scale, multi-national study involving nearly one million participants has found “a consistent and robust” increased risk of haematological malignancies in children exposed to radiation through CT scans.

Data from the EPI-CT study, published in Nature Medicine (link here), show a clear link between cumulative doses of radiation to the bone marrow from CT scans and the risk of developing both myeloid and lymphoid malignancies, according to researchers who led the trial.

The findings signal the need to raise awareness among clinicians of this risk further “and continued strict application of radiological protection measures in medical settings through justification and optimisation of radiological procedures, particularly in paediatric populations,” the study authors stressed.

The risk to children and adolescents from low-dose exposure (<100 mGy), as normally emitted via diagnostic CT procedures, has not been determined.

While previous research indicated that repeated CT scans raise the risk of leukaemia, “studies were critiqued due to low statistical power, inadequate individual dosimetry and potential bias from confounding by indication”, according to the paper.

The EPI-CT study was designed to address the limitations of previous national studies to increase the accuracy of CT cancer risk estimates. It included 948,174 individuals who underwent CT examinations before the age of 22 in nine European countries, including the UK.

Analysis of the data showed a relationship between cumulative dose of radiation from CT scans and risk of all haematological malignancies, with an excess relative risk of 1.96 (95% confidence interval 1.10 to 3.12) per 100 mGy (790 cases), with similar findings for lymphoid and myeloid malignancies.

“With an average ABM dose of 8 mGy for a typical examination today (the average dose in the cohort in 2012–2014), this translates to about a 16% increased risk (95% CI 8% to 24%) of these rare malignancies per examination,” the investigators said.

In terms of absolute risk, the results indicate that for every 10,000 children examined at the current mean CT dose of 8 mGy, one to two persons would be expected to develop a haematological malignancy attributable to radiation exposure in the following 12 years, they added.

To mitigate this risk where possible, clinicians should ensure that CT scans are justified, that radiation doses are kept to a minimum while maintaining necessary image quality, and that delivered doses are monitored, the authors stressed.