A new study authored by U. California-Berkeley researchers suggests that diagnostic X-rays used for a variety of medical purposes may increase the risk of developing leukemia for children.

The report, published in the October issue of International Journal of Epidemiology, indicated a correlation between children who had been diagnosed with acute lymphoid leukemia – a type of cancer that causes the overproduction of white blood cells in bone marrow – and those who had been previously exposed to X-rays. The study found that children diagnosed with ALL were almost twice as likely to have been exposed to three or more X-rays.

“Initially, we were under the impression that the doses of radiation (in X-rays) would be too low to cause harm, so this came as a surprise,” said Karen Bartley, UC Berkeley doctoral student in epidemiology and lead author of the study.

The aggregated data show that while the risk of certain similar variations such as acute myeloid leukemia or T-cell leukemia did not increase with exposure to X-rays, the risk of ALL did. Moreover, the risk of a specific type of ALL known as B-cell leukemia significantly increased for children after just one X-ray.

Researchers asked mothers of 827 children diagnosed with leukemia to provide details about their child’s radiological history. Information was then collected from the parents’ reports of how many times their child, at least 12 months prior to being diagnosed, had been exposed to X-rays, including possible instances of exposure during pregnancy.

The data, collected from 35 counties in Northern California between 1995 and 2008, comes from the Northern California Childhood Leukemia Study – a case-control study that investigates local factors that cause leukemia in children.

Leukemia, the most common form of cancer in children, accounts for about one-third of all childhood cancer cases. Patricia Buffler, a professor of epidemiology at UC Berkeley and the study’s principal investigator, said the NCCLS was formed in part because, at the time it was founded, approximately 95 percent of childhood leukemia cases could not be linked to direct causes. The study, unlike the other epidemiological studies during the mid-1990s, focused on collecting biological materials like blood, urine and bone marrow in order to learn more about the disease.

“The major point that we want to get across is the potential concern that needs to be followed up on with closer attention and additional research,” Bartley said. “Ultimately, the clinicians decide.”