Leukaemia incidence in the Techa River Cohort: 1953-2007.

Previous studies suggest that both acute and protracted radiation exposures are associated with an increased risk of leukaemia (Curtis et al, 1994; Preston et al, 1994; Gilbert, 2009; Daniels and Schubauer-Berigan, 2011). An estimate of the proportion of leukaemia cases associated with natural background exposures has been made using published risk models (Kendall et al, 2011) and variation in the risk of childhood leukaemia associated with variation in natural background radiation levels observed (Kendall et al, 2013). The challenge remains to quantify and describe the dose–response relationship from low dose (<100 mGy) and low-dose-rate exposures (<5 mGy h−1) (Wakeford and Tawn, 2010). The current analyses focus on characterising the radiation effects on the risk of leukaemia and other haematopoietic malignancies over more than 50 years in a population that received low-dose-rate radiation exposures as a consequence of environmental contamination arising from the production of plutonium for nuclear weapons in the Russian Southern Urals. The nature (i.e. protracted exposure to multiple radionuclides, including caesium and strontium) of the exposures is similar to those experienced as a consequence of nuclear accidents such as those in Chernobyl and Fukushima. The Techa River Cohort (TRC), as described previously (Kossenko et al, 2005; Krestinina et al, 2005, 2007, 2010), is a unique resource for estimating cancer risks following chronic exposure to environmental radiation in a general population. It is one of few human populations protracted strontium exposure, a radionuclide which concentrates in the bone and is thus of great relevance for leukaemia studies. The TRC members were exposed to external γ-radiation exposure from contaminated river sediments and flood plain soil and internal exposure from radionuclides including strontium89, strontium90, and caesium137 from the consumption of contaminated water, milk, and food products following the release of radioactive waste into the River by the Mayak Radiochemical Plant between 1949 and 1956 (Akleyev et al, 1995; Degteva et al, 2006; Tolstykh et al, 2011). We previously reported a statistically significant, dose–response relationship between the red bone marrow (RBM) dose and risk of leukaemia using an earlier dosimetry system (Techa River Dosimetry System (TRDS-2000)) (Krestinina et al, 2005; Ostroumova et al, 2006; Krestinina et al, 2010). The development of a better understanding of the nature of the releases, improved radiation transport and bio-kinetic models, and efforts to further individualise dose estimates led to the development of an updated dosimetry system (TRDS-2009) (Degtevea et al, 2012; Napier et al, 2013). Improvements to the strontium biokinetic model (Shagina et al, 2003) and the incorporation of previously unavailable information about the composition and timing of radionuclide releases into the river are of particular relevance to RBM dose estimates. Although the TRDS-2009 doses have been used for analyses of solid cancer mortality risks (Schonfeld et al, 2013), the work reported here is the first to make use of the improved doses in risk estimation for haematological malignancies. The primary focus in this work concerns estimating radiation risk for non-chronic lymphocytic leukaemia (non-CLL); however, we also describe the results for all leukaemias as a group, CLL, and other haematological malignances.