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).

This work focuses on the direct epidemiological assessment of the risks of radiation-induced leukaemia and thyroid cancer in emergency workers (EW) after the Chernobyl accident. The Russian National Medical Dosimetric Registry (RNMDR) contains data for 168,000 EW as of January 1, 1996. The analysis relates to 48 leukaemias and 47 thyroid cancers, diagnosed and verified. Radiation risks are estimated by comparing the EW data with national data for a male population of the same age distribution. For leukaemia, an excess relative risk per Gy (ERR/Gy) of 4.30 (95% CI: 0.83, 7.75) is obtained, while the excess absolute risk per 10(4) person-years (PY) Gy (EAR/10(4)PY Gy) is found to be 1.31 (95% CI: 0.23, 2.39); for thyroid cancer an ERR/Gy of 5.31 (95% CI: 0.04, 10.58) is obtained, and an EAR/10(4)PY Gy of 1.15 (95% CI: 0.08, 2.22).

This paper presents an analysis of data of the Russian National Medical and Dosimetric Registry on the incidence of leukaemia among 155 680 male Chernobyl accident emergency workers (EWs) who were resident in the Russian Federation (RF) for the period from 1986 to the end of 1993. The system of collection and verification of data on leukaemia is described. 48 cases of leukaemia among EWs were identified in 1986 - 1993. The principal analysis includes 34 leukaemia cases occurring more than two years after first exposure. The analysis was carried out for all leukaemia and leukaemia excluding chronic lymphocytic leukaemia (CLL), separately. Distributions of leukaemia cases by age, time of diagnosis since entry into the Chernobyl zone, radiation dose, date of entry into the Chernobyl zone, duration of stay in the region of Chernobyl were calculated. To evaluate leukaemia risks associated with various factors the case - control methodology was used. Radiation dose, date of entry into the zone, duration of stay in the zone were used as risk factors. No significant associations between leukaemia risks and the investigated factors were found. Calculation of the standardised registration ratios (SRR) revealed a significant increase in the registration of leukaemia among all EWs (SRR = 205, 95% confidence interval (CI) 136 - 297) and the EWs arriving in the zone during 1986 - 1987 (SRR = 200, 95% CI: 127 - 300) compared with the general male population of the RF in 1991 - 1993. However, raised SRRs may be accounted for by the differences in medical screening in the compared populations, particularly the efforts made to identify leukaemia cases among the EWs. The absence of a dose-related trend for leukaemia indicates that this explanation is likely to be correct.

In 1986, immediately after the Chernobyl accident, the Ministry of Public Health of the USSR adopted a large-scale programme to establish in the country the All-Union Distribution Registry of persons affected by radiation. Towards 1992 (by the time of the disintegration of the USSR) the data base of the Registry included medical and dosimetric information for 659,292 men and that for 284,919 emergency workers (liquidators). All republics of the former Soviet Union as well as a wide range of scientific and practical institutions were involved in establishment of the registry. At present there is medical and dosimetric information for 370,120 men, including that for 159,027 liquidators of the accident, in the National Chernobyl Registry of Russia. Medical information (added annually) and dosimetric data allow radiation-epidemiological studies to be carried out on determination of possible dose dependence of morbidity, invalidism and mortality indices for persons affected by radiation and to compare actual data with prognostication estimates. In particular, epidemiological studies conducted in accordance with the case control technology of thyroid cancer diseases in children of the Bryansk region made it possible to determine a value of relative risk at the dose of 1 Gy which is equal to 7.15 (1.52; 33.8).

This paper presents an analysis of data of the Russian National Medical and Dosimetric Registry (RNMDR) on the incidence of leukemia among Chernobyl accident emergency workers (EWs) who are resident in the Russian Federation (RF) for the period from 1986 through the end of 1993. It describes the system of a collection and a verification of data on leukemia. The analysis deals with 48 cases of leukemia diagnosed and verified among EWs. Distributions of leukemia cases by date of diagnosis, age, radiation dose, date of entry into the Chernobyl zone, date of exit from the zone, duration of stay in the region of Chernobyl were calculated. To evaluate leukemia risks associated with various factors the case-control methodology was used. Radiation dose, date of entry into and date of exit from the zone, duration of stay in the zone were used as risk factors. No significant associations between leukemia risks and the investigated factors were found. Calculations of standardised incidence ratios (SIR) revealed a significant increase in the incidence of leukemia among EWs of all dates of entry into the zone (SIR: 205, 99% confidence interval (CI): 105-305) and EWs entered the zone in 1986-1987 (SIR: 200, 95% CI: 118-282) compared to the general male population of the RF in 1991-1993.

The work focuses on direct epidemiological assessment of radiation risks in induction of leukemia and thyroid cancer in emergency workers after the Chernobyl accident. The Russian National Medical Dosimetric Registry compiles data for 168 thousand emergency workers as of 01.01.1996. Analysis is performed of 48 leukemias and 47 thyroid cancers diagnosed and verified in emergency workers. The estimated radiation risks are: for leukemia excess relative risk per Gy (ERR/Gy) is 4,30 (95% CI = 0,83; 7,75), excess absolute risk per 104 PY Gy (EAR/104 PY Gy) is 1,31 (95% CI = 0,23; 2,39); and for thyroid cancer ERR/Gy is 5,31 (95% CI = 0,04; 10,58), EAR/104 PY Gy is 1,15 (95% CI = 0,08; 2,22).