A case-control analysis of leukemia in accident emergency workers of Chernobyl.

We estimated the radiation-induced risk of leukemia in 162,684 Chernobyl accident emergency workers (EWs) using the data of the Russian National Medical and Dosimetric Registry (RNMDR). A system was established for the collection and verification of data in 55 cases of leukemia from 1986 to 1995. The principal analysis included 41 leukemia cases that occurred more than 2 years after the first exposure to radiation. The case-control methodology was used to evaluate the risk of leukemia associated with various factors. Radiation dose, effective exposure dose rate, date of entry into the Chernobyl zone (ChZ), and the duration of stay in the zone were used as risk factors. The relationship between the date of entry and the duration of stay in the zone was investigated. All cases of leukemia, excluding chronic lymphocytic leukemia (CLL), were analyzed. An analysis was also performed on all EWs and on the EWs who worked in the zone from 1986 to 1987 (EWs of 1986 to 1987). No significant association was found between the risk of leukemia and the factors we investigated. Nevertheless, the relative risk estimates for leukemia, excluding CLL, were greater than the value for all leukemia and were greater than one. The estimated excess relative risk (ERR) per Gy was greater for all EWs [ERR = 1.33, 95% confidence interval (CI): -6.25, 8.90 for all leukemia, and ERR = 15.59, 95% CI: -24.92, 56.11 for leukemia, excluding CLL] compared with EWs of 1986 to 1987 (ERR = 0.28, 95% CI: -5.84, 7.41 for all leukemia, and ERR = 9.43, 95% CI: -20.0, 38.86 for leukemia, excluding CLL).