CT scans, commonly used in medical imaging, may increase the risk of brain tumours, a study has found.
However, they deliver higher radiation doses, and can especially affect children who are more susceptible to radiation-related malignancies than adults, researchers said.
The most common malignancies caused by radioactivity among children and young adults are leukemia and brain tumours.
Researchers from Netherlands Cancer Institute evaluated leukemia and brain tumour risks following exposure to radiation from CT scans in childhood.
For a group of 168,394 Dutch children who received one or more CT scans between 1979 and 2012, researchers obtained cancer incidence and vital status by record linkage.
They surveyed all Dutch hospital-based radiology departments to ascertain eligibility and participation. In the Netherlands, paediatric CT scans are only performed in hospitals.
Overall cancer incidence was 1.5 times higher than expected. For all brain tumours combined, and for malignant and nonmalignant brain tumours separately, dose-response relationships were observed with radiation dose to the brain.
Relative risks increased to between two and four for the highest dose category. The researchers observed no association for leukemia. Radiation doses to the bone marrow, where leukemia originates, were low.
They caution that this pattern of excess cancer risk may be partly due to confounding by indication, because the incidence of brain tumours was higher in the cohort than in the general population.
CT scans are sometimes used to identify conditions associated with an increased tumour risk; the reason these children had CT scans may be associated with their risk of developing cancer.
"Epidemiological studies of cancer risks from low doses of medical radiation are challenging, said the study's principal investigator, Michael Hauptmann, from Netherlands Cancer Institute.
"Our careful evaluation of the data and evidence from other studies indicate that CT-related radiation exposure increases brain tumour risk," said Hauptmann.
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