Low-dose rate radiation exposure and leukemia risks in the Mayak Worker and Techa River cohorts

Alexander V. Aklyeev, Urals Research Center for Radiation Mediciine 
Faith G. Davis, University of Edmonton 
Wan-Ling Hsu, Radiation Effects Research Foundation 
Nina Koshurnikova, Southern Urals Biophysics Institute 
Lyudmila Yu. Krestinina, Urals Research Center for Radiation Mediciine 
*Dale L Preston, Hirosoft International 
Sara Schonfeld, International Agency for Research on Cancer 
Mikhail E. Sokolnikov, Southern Urals Biophysics Institute 

Keywords: leukemia, low dose rate, radiation helath effects, dose reponse

Elevated leukemia risks were apparent among atomic bomb survivors 2 to 5 years after exposure and radiation effects on leukemia risks have been carefully studied in the atomic bomb survivors and many other radiation exposed populations. The atomic bomb survivor studies provide strong evidence for a radiation effect with large time- and age-at-exposure-dependent excess risks and an upward curving dose response following acute exposures to doses ranging up to about 2 Gy. Studies of populations of people exposed as a consequence of plutonium production that began in 1948 at the Mayak Production Association in the Russian Southern Urals provide unique opportunities to investigate the magnitude and nature of protracted low dose rate exposures. The Mayak worker cohort includes about 26,000 men and women who worked in one of the main plants (reactors, radiochemical, and plutonium production) or selected auxiliary plants at Mayak. During the early years of Mayak operations significant amounts of radioactive material was released into the Techa River resulting in the contamination of river water and flood plain soils in about 40 villages along the river. The Techa River cohort includes about 30,000 people of all ages who were born before 1950 and lived in one or more Techa riverside villages between 1950 and 1960. Analyses of the leukemia risk carried out over the last 18 years in these two cohorts have clearly demonstrated radiation-dose-associated rate increases for these low-dose rate exposures. Recent years have seen extended follow-up and significant improvements in the dosimetry for both the Mayak worker and Techa River cohorts. In this presentation we describe the nature of these cohorts, and present risk estimates based on the individual doses computed using the latest dosimetry systems for the two cohorts. Low-dose rate radiation exposures are significantly associated with increased leukemia risks in both cohorts with no evidence against linearity. The results for Mayak workers and, to a lesser extent, Techa River residents, suggest that the largest relative risks were associated with exposures received shortly before diagnosis with or death from leukemia but that the elevated risks appear to continue throughout life. In addition to discussion of the latest result in these cohorts, we will contrast the findings in these studies to leukemia risk estimates obtained in recently updated analyses of the atomic bomb survivor cohort.