Radiation Risk Assessment of Leukemia in Children of Belarus

s. Results of an analysis of the incidence in the acute childhood leukemia in Belarus in 1980-2004 carried out on the basis of ecological model are discussed in the report. Published data of the Belarusian Republican Registry of Childhood Hemoblastoses and Hemopoiesis Depressions as well as the Belarusian Cancer Registry were used in the analysis. Only mixed childhood subgroup was considered without separating boys and girls. It was found that a shorttime increase in the incidence of leukemia in children of Belarus (0 – 14 years at the time of diagnose) occurred in Belarus soon after the Chernobyl accident. The increase is statistically significant. After 1992 a decline in the childhood leukemia incidence began. As a result, the incidence in the childhood leukemia of Belarus after the period 1986-1992 became less than it was before the Chernobyl accident. 708 cases of acute leukemia were registered in Belarus in the period 1986-1992. The number of expected leukemia in this period was assessed to be approximately 625 cases. These data give the standardized incidence ratio for the period 1986-1992 equal to 1.13 with 95% CI from 1.02 to 1.26. Radiation risks and attributive risk of leukemia incidence were assessed on the basis of an assumption that observed short-time increase in the childhood leukemia in Belarus had radiation origin. They are for the period 1986-1992: ERR = 7.8% per 1 mSv (95% confidential interval is from 1.0 to 15.4% per 1 mSv), EAR = 30.1 cases per 10 PYSv (95% confidential interval is from 3.9 to 59.2 cases per 10 PYSv), AR = 11.7% (95%CI is from 1.5 to 23%). Introduction. It is well known that hematopoietic tissues and organs are very sensitive to carcinogenic impact of ionizing radiation. This was established in epidemiological studies that have shown an increase of leukemia in different irradiated groups. It was found that infants and children have the highest radiation risks of leukemia [1-3]. This makes leukemia in infants and children a qualitative indicator of irradiation. A number of epidemiological studies [4-15] were performed after the accident at the Chernobyl NPP in order to study the possible increase in the leukemia incidence in countries that were affected as a result of this accident. Results of these studies are quite controversial. Petridou et al [4] found an elevated increase in leukemia in infants (from 0 to 11 months after birth) born in Greece in the period from 1 July 1986 to 31 December 1987. The incidence in leukemia in this cohort was by factor 2.6 (95% confidence interval, 1.4 to 5.1: p(2-tailed) ≈ 0.003: 12 cases in the ‘exposed’ and 31 cases in the control group) higher than in infants born in the periods 1/1/1980 to 31/12/1985 and 1/1/1988 to 31/12/1990 (control group). It was also found that the incidence in leukemia in infants born in contaminated areas in the period from 1 July 1986 to 31 December 1987 correlated with a level of a radioactive contamination. These results were established for areas with low contamination (less than 100 Bq/kg of soil), intermediate (999-1000 Bq/kg) and high contamination (> 1000 Bq/kg) with Cs. According to our assessment, such contamination of soil corresponds with levels of the surface