Getting a single CT scan during childhood doesn't appear to increase a child's risk of a future brain tumor, leukemia or lymphoma, new research finds, but getting four or more scans more than doubles the chances.

CT scans use low-dose radiation, which can damage cells. Past evidence about the risks of cancer from these scans in children 18 and younger was conflicting, researchers said.

For this study, data was evaluated on more than 7,800 children in Taiwan who were diagnosed with intracranial tumors, leukemia or lymphoma between 2000 and 2013. These kids were matched with more than 78,000 controls within the Taiwanese national health system.

The researchers then compared tumor rates for those children who had had CT scans versus those who had not.

While the study found no increased risk after one CT scan, children who received two to three scans had an increased risk of intracranial tumors. Those children who received four or more CT scans had a more than twofold risk of intracranial tumors, leukemia and non-Hodgkin lymphoma.

The findings were published April 24 in the Canadian Medical Association Journal.

"Our work reinforces the importance of radiation protection strategies, addressed by the International Atomic Energy Agency," said author Yu-Hsuan Joni Shao, of the College of Medical Science and Technology at Taipei Medical University in Taiwan.

"Unnecessary CT scans should be avoided, and special attention should be paid to patients who require repeated CT scans," Shao said in a journal news release.

The study found that younger children appeared to be more at risk of developing cancer from repeated CT scans.

"Parents and pediatric patients should be well-informed on risks and benefits before radiological procedures and encouraged to participate in decision-making around imaging," the authors said.