The risk of developing leukemia is significantly increased for the 110,654 workers who helped clean up after the 1986 Chernobyl nuclear power plant accident. The results of this 20-year study may help scientists to better define the cancer risk associated with low doses of radiation from medical diagnostic radiation procedures such as computed tomography scans.

This study is the largest and longest to date involving Chernobyl cleanup workers who worked at or near the nuclear complex in the aftermath of the accident. The study describes the increased risks of leukemia among these works between 1986 and 2006, including greater than expected numbers of cases of chronic lymphocytic leukemia (CLL). In the past, many experts did not consider CLL to be associated with radiation exposure.

Overall, 137 cases of leukemia occurred among the workers over the 20-year span of the study, with 16% of those cancers being attributable to the Chernobyl radiation exposure. The findings shed light on the thorny issue of estimating cancer risk from low doses of radiation. This issue is of importance to miners, nuclear workers, and anyone who is chronically exposed to low levels of radiation at work, along with patients who receive sizeable radiation doses when undergoing medical diagnostic tests.

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“Low doses of radiation are important,” said the lead researcher Lydia Zablotska, MD, PhD, an associate professor of epidemiology and biostatistics at UCSF. “We want to raise awareness of that.”

For many years, the best estimates of how much leukemia is associated with moderate or low doses of radiation came from long-term studies of the survivors of the 1945 atomic bomb detonations over Hiroshima and Nagasaki, Japan, during World War II. Since these atomic bomb survivors were bathed in gamma or neutron rays, extrapolating data from them is problematic. Someone who undergoes a CT scan in the United States is exposed to x-rays, which are a different type of radiation. The new work on Chernobyl cleanup workers helps to bridge the gap, because the doses received by the cleanup workers fall somewhere between the high level received by the Japanese atomic bomb victims and the lower levels received by people who undergo extensive medical scans.

This study challenges the idea that CLL is not linked to radiation exposure, which seemed to be supported by earlier studies of atomic bomb survivors. Zablotska explained that the genetic makeup of the Japanese population may have hidden the risk of CLL, because they are much less likely to develop CLL anyway. While CLL accounts for only 3% of all cases of leukemia in Japan, it accounts for about one-third of all leukemia cases in the United States and 40% of all cases of leukemia in Ukraine.

This study was published in Environmental Health Perspectives (2012; doi:10.1289/ehp.1204996).