Radiation Risk Assessment of Leukemia in Children of Belarus
M. V. Malko
Joint Institute of Power and Nuclear Research-Sosny,
National Academy of Sciences, Minsk, Belarus

Abstracts. 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. Publisheddata 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 ofdiagnose) occurred in Belarus soon after the Chernobyl accident. The increase is statisticallysignificant. After 1992 a decline in the childhood leukemia incidence began. As a result, theincidence 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 wereassessed 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 104
PYSv (95% confidential interval is from 3.9 to 59.2 cases per 104 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 ofionizing radiation. This was established in epidemiological studies that have shown an increase ofleukemia 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 aresult 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 inthis 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 witha 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
137
Cs. According to our assessment, such contamination of soil corresponds with levels of the surface- 151 -

contamination in this isotop less than 5 kBq/m2, 5 to 50 kBq/m2 and higher than 50 kBq/m2. Petridou et al[4] explained their findings as a result of an in utero irradiation.
The authors [4] established also some small and statistically insignificant increase in theleukemia incidence in children at the age 12-47 months at the time of diagnoses exposed in utero to
Chernobyl radiation. The ratio of the incidence in leukemia of such children to the incidence of children
born in the period 1/1/1980-31/12/1985 and 1/1/1980-31/12/1990 was equal to 1.1 (95% confidence
interval, 0.8 to 1.5: p(2-tailed) ≈ 0.56: 43 cases in the ‘exposed’ and 266 cases in the control group).
Studies of the infant leukemia were performed also in Germany and Belarus [5-7] by using
similar temporal cohorts as in the report [4]. Michaelis et al [5,6] compared incidence rates of infants bornin the former FRG in areas with the ground contamination with the 137Cs < 6 kBq/m2, 6 –10 kBq/m2, > 10
kBq/m2 with the incidence of “unnexposed in utero” infants. They have found also an increase in theincidence in infant leukemia in West Germany, although smaller than in Greece (rate ratio: 1.48 with 95%
CI: 1.02 to 2.15; 35 cases in the ‘exposed’ and 143 in the control group). However, no correlation between
rate ratios and level of contamination was found in the German studies. Therefore authors [5,6] concluded
that excess in the leukemia incidence occurred in infants in West Germany after the Chernobyl accident
was not related to radiation.
An increase in the infant leukemia was observed after the accident in Belarus [7]. The rate ratio
for entire Belarus including Gomel and Mogilev regions was found equal to 1.26 (95% CI: 0.76 to 2.10:
17 cases in the ‘exposed’ and 89 in the control group). In case of Gomel and Mogilev regions combined
together the rate ratio was equal to 1.51 (95% CI: 0.63 to 3.61: 6 cases in the ‘exposed’ and 27 in thecontrol group). These findings indicate the existence of qualitative correlation between the level ofincrease and level of contamination of Belarus. In this respect the Belarusian data agree well with data
established by Petridou et al [4]. However, excess in the infant leukemia observed in ‘exposed’ cohorts ofGomel and Mogilev regions was lesser than in Greece despite the fact that average contamination of theseregions is higher than the maximal contamination in Greece. This and the absence of statisticalsignificance of rate ratios in case of the Gomel and Mogilev as well as entire Belarus was considered byauthors [7] as an evidence that increase in the infant leukemia in Belarus had no link to in utero irradiation
caused by the Chernobyl accident.
Controversial results were established also in epidemiological studies of the incidence in leukemia
in children. Auvinen et al [8] compared incidence rates in leukemia in children in Finland observed in
1986-1988 and 1989-1992 with incidence rate registered in 1976-1985. According them a relative risk
assessed for the period 1986-1988 was equal to 0.95 (95%CI from 0.80 to 1.35) and for 1989-1992 – 1.01
(95%CI from 0.87 to 1.17). An excess relative risk equal to approximately 7% per mSv (95%CI from –27% to 41%) have been estimated in this study for the period 1989-1992.
An analysis of childhood leukemia observed in 1986-1992 in areas with different surface
contamination was undertaken in Sweden [9]. For all cases diagnosed after May 1986 in highly
contaminated areas (> 10 kBq/m2) compared with areas of low contamination (< 10 kBq/m2) authors
estimated the odds ratio equal to 0.9 (95%CI from 0.7 to 1.3). For acute lymphoblastic leukemia inchildren aged under 5 years at diagnoses the odds ratio in highly contaminated areas compared with areasof low contamination was 1.2 (95%CI from 0.8 to 1.9). Dose-response analysis undertaken by authors [9]showed no correlation between the degree of contamination and the incidence of childhood leukemia.
A slight increase in the incidence in childhood leukemia in Belarus was observed soon after theaccident at the Chernobyl NPP in Belarus [10,11]. 655 cases of leukemia in children aged from 0 to 15
years were observed in Belarus in 1979-1985 and 708 in 1986-1992. The rate ratio assessed for these
periods is 1.034 (90% CI from 0.946 to 1.131). The statistical power of the rate ratio was very low- 152 -

(χ2=0.383, p = 0.268). The observed increase in the childhood leukemia in Belarus after the Chernobyl
accident, as can be seen from these data, was statistically not significant. No statistical significant change
in the incidence in leukemia in the Belarusian children was found also in the report [12].
The importance of the incidence in the childhood leukemia that is a qualitative indicator ofirradiation requires a careful analysis of different aspects of the childhood leukemia in Belarus before andafter the accident. And this is the main aim of the present report.
Materials and Methods.
Data of the Belarusian Republican Registry of Childhood Hemoblastoses and Hemopoiesis Depressions(number of registered cases of leukemia) that were published previously [10-12, 15-17] were used in thereport. The work on creation of the Registry has been begun in 1988. In course of it specialists of theInstitute of Hematology and Transfusion of the Ministry of Health Care of the Republic of Belarus
assessed under the scientific supervision of Prof. E.P.Ivanov all information on childhood hemoblastoses
and hemopoieses. This information came to the Institute of Hematology and Transfusion from oncologicaldispensaries, clinics and polyclinics as well as from hematological consultative establishments. It includes
the following data: the name and address of the patient, age, date, place of diagnosis, ICD number ofdiagnosis, and the diagnostic method (e.g. biopsy, autopsy, myelogram, immunohistochemical method
used, etc.) [10-12]. These data are available for each oblast (region) of Belarus, the city Minsk (capital ofBelarus) and for the entire country. There are 6 oblasts in Belarus: Brest, Gomel, Grodno, Minsk, Mogilev
and Vitebsk.
Data of the Belarusian Cancer Registry for the period 2001-2004 [18-20] were also used in thepresent report. Numbers of children used in the analysis were determined on the basis of population
census of the Republic of Belarus [21] and statistical handbooks [22-24]. The analysis was carried out for
combined children’s population without separate consideration of boys and girls. Using data on theleukemia incidence as well as other data time-averaged radiation risks of the incidence in childhood
leukemia in Belarus were assessed.
The excess absolute risk was assessed on the basis of the following simplified expression:
Oj − Ej.
EAR j =(1)j
N PYSv
Here EAR j - excessive absolute risk in jth period of time, O j and E j - numbers of observed andj- number of person-years-sievert in the jth period.
expected leukemias in this period respectively, N PYSvj
is determined by the expression:
The value of N PYSvn

N PYSv = ∑ H i , j .
j

Coll

(2)

i =1

Here

H i , j collective equivalent dose of the whole body irradiation accumulated from theCollbeginning of irradiation to the end of the ith year in the jth period.
The excess relative risk was assessed by using the formula:(O j / E j ) − 1 ,ERR j = jj
N PYSv / N PY

- 153 -

(3)j
- number of person-years in the jth period of time.
where N PY

The attributive risk , AR j , was assessed on the basis of the expression:
AR j = 100% ⋅Oj − Ej
Oj(4)

Results and discussion.

Doses of irradiation
Table 1 presents cumulative doses of the whole body irradiation of the total Belarusian childhood
population as a result of the Chernobyl accident. Data given in this table were taken from Table 3 of thereport [25].
As can be seen from this table, collective and mean individual doses of the whole body irradiation
to children of Belarus increased rapidly up to 1989 and then decreased slowly after achieving somemaximal values. This temporal pattern of irradiation doses appears in case of children because thechildhood subpopulation is an open system. Its composition is determined through two continuous flows.
One flow is directed from outside to inside. This is the flow a newborn children. It adds irradiation doses
to already accumulated doses. The second flow is directed from inside to outside. This is a flow of persons
that achieved the age of 15 years. They leave the subpopulation of children carrying a fraction of
accumulated irradiation doss to the subgroup of adolescents and adults.
Table 1. Cumulative collective and mean individual doses of the whole body irradiation of thechildhood population of Belarus as a result of the Chernobyl accident.
Collective
IndividualCollective
Individual
Year
Year
104 PSv
mSv
104 PSv
mSv
1986
0.25691
1.122041996
0.25159
1.17229
1987
0.3722
1.61069
1997
0.21916
1.05311988
0.42971
1.84569
1998
0.184280.919721989
0.45005
1.922961999
0.14706
0.76311990
0.43956
1.877172000
0.10972
0.58983
1991
0.42278
1.81315
2001
0.077120.43181
1992
0.38629
1.669622002
0.05883
0.34451993
0.34885
1.525412003
0.04834
0.296061994
0.31089
1.38177
2004
0.03834
0.24613
1995
0.282071.28037

It was demonstrated in the report [25] that the main contribution to irradiation doses in Belarus
gave irradiation in 1986-1989. After 1989 a significant decrease in irradiation doses occurred in Belarus.
All those persons that were members of the children’s subpopulation in 1986-1989 left this subgroup in
2004 because achieving of the age 15 years. And this caused significant decrease of irradiation doses of
the children’s subgroup.

Incidence in acute leukemia in children of Belarus
Figure 1 and Table 2 present time-averaged incidences in the acute childhood leukemia in different
regions of Belarus. Three time periods are shown here. They are 1980-1985, 1986-1992 and 1993-2000.
The time after the Chernobyl accident was divided in two periods: 1986-1992 and 1993-2000.
- 154 -

As can be seen from Fig.1 and Table 2, a short-time increase in the childhood leukemia occurred
immediately after the Chernobyl accident in all regions of Belarus except the Mogilev oblast. In case of
the Mogilev region a permanent decrease in the incidence in the childhood leukemia was observed in the
period 1980-2000. The most plausible reason of this temporal pattern of the incidence in the childhood
leukemia in case of the Mogilev region could be an incorrectness of the empirical data established for thisregion before the Chernobyl accident.
Data presented in Fig.1 and Table 2 demonstrate that time-averaged incidence rates in practically all
regions of Belarus as well as in the entire Belarus in 1993-2000 were lower than in 1980-1985. This is an
4.6

Brest region

Gomel region

4.0

4.4

Cases in 100,000

Cases in 100,000

4.2

3.8

3.6

3.4

4.0
3.8
3.6
3.4

3.2
3.2

3.0

3.0

1980-1985

1986-1992

1993-2000

1980-1985

Time periods

5.0

Grodno region

4.2

1986-1992

1993-2000

Time periods

city Minsk

4.8
4.6

Cases in 100,000

Cases in 100,000

4.0
3.8
3.6
3.4

4.4
4.2
4.0
3.8
3.6
3.4

3.2
3.2
3.0

3.0
1980-1985

1986-1992

1980-1985

1993-2000

1986-1992

1993-2000

Time periods

Time periods
4.4
Minsk region

4.8
4.6

4.0

Cases in 100,000

Cases in 100,000

Mogilev region

5.0

4.2

3.8
3.6
3.4

4.4
4.2
4.0
3.8
3.6
3.4

3.2

3.2
3.0

3.0
1980-1985

1986-1992

1980-1985

1993-2000

Vitebsk region

5.0

1986-1992

1993-2000

Time periods

Time periods

4.6

4.8

Belarus in total

4.4

4.6

Cases in 100,000

Cases in 100,000

4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0

4.2
4.0
3.8
3.6
3.4
3.2

2.8
3.0

2.6
1980-1985

1986-1992

1993-2000

1980-1985

1986-1992

1993-2000

Time periods

Time periods

Fig. 1. Time-averaged incidences in the acute childhood leukemia in different regions of Belarus.

- 155 -

Table 2. Incidence in the acute childhood leukemia in regions of Belarus in 1980-1985,
1986-1992 and 1993-2000.
Region
Cases
Person·years IR·105, a
SE·105, a
1980-1985
Brest
80
2,268,213
3.527
0.394
Gomel
80
2,385,799
3.353
0.375
Grodno59
1,588,899
3.713
0.483
City Minsk
90
2,002,278
4.495
0.474
Region Minsk
75
2,226,026
3.369
0.381
Mogilev
84
1,756,243
4.783
0.522
Vitebsk
70
1,843,033
3.798
0.454
Belarus538
13,349,317
4.030
0.174
1986-1992
Brest
108
2,793,433
3.866
0.372
Gomel
117
2,724,858
4.294
0.397
Grodno71
1,808,251
3.926
0.466
City Minsk
122
2,623,805
4.650
0.421
Region Minsk
103
2,518,720
4.089
0.403
Mogilev
86
2,024,855
4.247
0.458
Vitebsk
101
2,103,497
4.802
0.478
Belarus708
16,256,056
4.355
0.164
1993-2000
Brest
92
2,718,244
3.385
0.353
Gomel
104
2,642,182
3.936
0.386
Grodno77
1,932,447
3.985
0.454
City Minsk
113
2,647,839
4.268
0.401
Region Minsk
96
2,544,115
3.773
0.385
Mogilev
74
2,003,962
3.693
0.429
Vitebsk
64
2,145,307
2.983
0.373
Belarus620
16,758,117
3.700
0.149

indication of a decreasing trend of spontaneous incidence in the childhood leukemia in Belarus
The slight decline in the leukemia incidence in Belarus began already before the accident at the
Chernobyl NPP. This can be seen in Fig.2 that shows annual incidence rates in Belarus in the period 19801985 (left panel). The right panel of the Fig.2 displays annual incidence rates in the periods 1980-1985
and 1993-2004 combined together.
In case of data presented in the left panel of Fig. 2 only data of the Belarusian Republican Registry
4.7

Y =219.21089-0.10854 X
2
R = 0.61903, n = 6, P(2-tailed) = 0.06334

4.6

4.5

Cases in 100,000 children

Cases in 100,000 children

4.6

4.4
4.3
4.2
4.1
4.0
3.9
3.8

Y =47.99013-0.02218 X
2

R = 0.39071, n = 18, P(2-tailed) = 0.00554

4.4
4.2
4.0
3.8
3.6
3.4

3.7
1980

1981

1982

1983

1984

1985

1980

Years

1985

1990

1995

2000

2005

Years

Fig.2. Incidence in the childhood leukemia in Belarus in 1980-1985 (left panel) and in 1980-1985,
1993 –1994 (right panel).

- 156 -

of Childhood Hemoblastoses and Hemopoiesis Depressions were used. The data presented in the rightpanel of this figure were constructed by using data of the Belarusian Republican Registry of Childhood
Hemoblastoses and Hemopoiesis Depressions for the periods 1980-1985, 1993-2000 and data of theBelarusian Cancer Registry for the period 2001-2004 [18-20].
The decreasing trend in the childhood leukemia observed in Belarus before the Chernobyl accident
indicates the necessity to analyze the increase of the childhood leukemia in Belarus after the Chernobyl
accident on the basis of comparison of observed and expected incidences in this period of time. Threedifferent simplified methods can be used for assessment of expected incidence rates in the period 19861992. At first, expected incidence rates in the period 1986-1992 can be determined as arithmetic means ofempirical incidence rates estimated in periods 1980-1985 and 1993-2000. This method gives for the entire
Belarus the value 3.865·10-5 a-1 as the expected incidence rate for the period 1986-1992.
The second method of assessment is based on combining numbers of leukemia cases and personyears established in different periods of time. Assessment on the basis of Table 2 determines the total
number of leukemias in registered in children of Belarus in periods 1980-1985 and 1993-2000 equal to1,158 cases. The combined number of person-years in these periods is 30,107,434 person-years. Dividingof the first number by the second gives the value 3.846·10-5 a-1. It differs only by 0.5% from the value
assessed with the first method.
The third method in case of the entire Belarus is based on using the fitting expression shown in theright panel of Fig.2. It gives the value 3.877·10-5 a-1 that is practically the same as values assessed by using
two first methods. This means that any described methods can be used for estimation of expected timeaveraged incidence rates of the childhood leukemia in the entire Belarus.
The analogous methods can be used also by estimation of expected incidence rates in the period
1986-1992 for separate regions of Belarus.
Table 3 presents standardized incidence ratios (SIRs) of the childhood leukemia in the period 19861992 estimated as ratios of observed incidence rates in the childhood leukemia in the period 1986-1992 toexpected incidence rates in the same period 1986-1992 for separate regions of Belarus and for the entire
country. The second method for estimation of the expected incidences was used by assessment of SIRs
shown in this table.
As can be seen from Table 3, analysis on the basis of standardized incidence ratios demonstrates
an increase in the incidence in the childhood leukemia in the period 1986-1992 in all regions of Belarus
including the Mogilev region. The highest increase occurred in the Vitebsk region. It was statisticallysignificant only in this region. The lowest increase occurred in the Mogilev and Grodno regions.
The use of standardized incidence ratios instead of rate rates demonstrates the existence ofstatistical significance of the increase in the incidence of the childhood leukemia in the entire Belarus.

Table 3. Standardized incidence ratios of the childhood leukemia in Belarus in 1986-1992.
P(1-tailed)RegionSIR
95%CI of SIR
χ2 (1df)
Brest
1.121
0.881 - 1.426
0.864
0.184
Gomel
1.173
0.931 - 1.479
1.831
0.091
Grodno1.017
0.763 - 1.355
0.013
0.456
0.303
0.299
City Minsk
1.065
0.851 - 1.333
Region Minsk
1.141
0.893 - 1.457
1.116
0.146
Mogilev
1.011
0.777 - 1.314
0.00640.464
7.420
0.00326
Vitebsk
1.429
1.104 - 1.850
Belarus1.133
1.017 - 1.261
5.168
0.0123- 157 -

Radiation risks
It is clear, that any increase of the incidence in some cancer in population with the stabile age distribution(for example, in population of children) could be caused by two different reasons. At first, it can be a
result of an improved screening of this cancer. At second, it can arise due to appearance of new
carcinogen/carcinogens in the environment as well as a result of an increase in amounts ofcarcinogen/carcinogens that was/were in the environment before the increase in the incidence in thiscancer. In the first case the incidence rate has to reach some increased value that remains constant later. In
the second case, a decrease of the incidence will occur after some short-time increase in the incidence incancer. Data given in the present report show a short-time increase in the incidence in the childhood
leukemia in all regions of Belarus after the Chernobyl accident and the following decline. Such temporal
pattern excludes the screening improvement as a main reason of observed increase in the incidence in thechildhood leukemia in Belarus after the accident at the Chernobyl NPP. It is clear that appearance of new
carcinogen/carcinogens or increasing of their amount is responsible for observed change in the leukemia
incidence in Belarus after the Chernobyl accident.
It is remarkable that the observed short-time increase in the childhood leukemia manifested at thesame time when a constant decrease in the chemical pollution occurred in Belarus [26,27]. It began in
Belarus in seventies of the last century as a result of a transfer from the use of hard fuel to natural gas forelectricity and heat production. This caused a significant improvement in the environment of Belarus.
Starvation of industry and agriculture at the beginning of eighties contributed also very significantly to theimprovement of the environment in Belarus [26,27]. As a result of these processes the discharge ofdifferent pollutants into the environment of Belarus decreased by factors 2-3 in the period 1985-2004[26,27].
The decrease of antropogenic pollution caused by industry, agriculture etc occurred in Belarus
simultaneously with an increase of irradiation as a result of the Chernobyl accident. All these facts
indicate that radiation is the most probable factor that caused observed changes in the childhood leukemia
in Belarus after the Chernobyl accident because this change can not result from the decrease in the amountof chemical pollutants.
There is only one finding that contradicts with the assumption that the increase in the childhood
leukemia in Belarus after the accident at the Chernobyl NPP was caused by the impact of ionizing
radiation. As can be seen from Table 3 standardized incidence ratio of the childhood leukemia in the
Vitebsk region is the highest in Belarus. However this region was practically not affected by the
Chernobyl accident [28]. Amount of radioactive substances deposited in this region is lower than in theGomel region approximately by three orders in magnitude [29]. A question arises. If radiation were theorigin of the observed increase in the childhood leukemia in Belarus after the Chernobyl accident why thestandardized incidence ratio of the childhood leukemia in the clean Vitebsk region is than in the highcontaminated Gomel region?
There is a plausible answer on this important question. Probable the high value of the standardized
incidence ratio of the incidence in the childhood leukemia in the clean Vitebsk region could be a result of
the migration of inhabitants of high-contaminated territories of the Gomel and Mogilev regions to thisregion.
The migration began soon after the accident at the Chernobyl accident. In first 10 years after the
Chernobyl accident 842.6 thousand of the Belarusian citizens or 8.4% of the total population changed theplaces of their living in borders of Belarus [30]. The internal migration (moving in borders of Belarus) was
especially high in contaminated territories. According to information [31], approximately one sixth of
inhabitants of the high-contaminated Slavhorod district (Mogilev oblast) left their contaminated- 158 -

settlements during three first years after the Chernobyl accident. The similar situation arose in othercontaminated districts of this region. The process of migration was even more pronounced incontaminated areas of the Gomel oblast [30].
The total number of people that changed their place of residence in borders of Belarus in 1986-2000
is 1,500,000 or 15% of the averaged population that was approximately 10 Million persons in this period[30].
The internal migration in Belarus from contaminated regions of Belarus was occurring partly as aresult of an implementation of the State Program of minimization of the Chernobyl consequences. On thisway about 135,000 persons were resettled from contaminated to clean territories [32]. Approximately
200,000 persons migrated from contaminated areas of Belarus without any assistance of the state [33].
Simultaneously with internal migration an intensive external migration began in Belarus after theaccident at the Chernobyl NPP. As a result of it only in 1990-2000 the country was left for other states of
the world 675.1 thousand of the Belarusian citizens [30]. This is 6.75% of the total population of Belarus.
Significant fraction of people that emigrated from Belarus after the accident at the Chernobyl NPP
lived on the territories affected by this accident. For example, approximately 130 thousand of persons of
the Jewish nationality immigrated to Israel from contaminated areas of Belarus and the Ukraine [34].
About 50% persons from this number lived before the emigration in high-contaminated territories ofBelarus.
It is evident that external and internal migration influences significantly the possible correlation
between incidence rates in different disease and levels of a radioactive contamination caused by the
Chernobyl accident. This influence had to be very significant in case of rare diseases such as the childhood
leukemia. This indicates that more correct analysis of radiation risks of the childhood leukemia caused in
Belarus as a result of the Chernobyl accident can be established only on the basis of data established forthe total country.
Radiation risks of the childhood leukemia assessed on the basis of an assumption that increase in
the incidence in the childhood leukemia observed in Belarus after the Chernobyl accident were assessed in
the present report. Results of this assessment are presented in Table 4. They were estimated for two
periods: 1986-1992 and 1986-2004. Data estimated by Auvinen et al [8] are shown also in Table 4 (fourthcolumn).
Table 4. Radiation risk of the incidence in the childhood leukemia.
This report
Auvinen et al [8]Parameters
1986-1992
1986-2004
1989-1992
Person-years
16,256,056
39,698,347
Observed cases
708
1,567
Expected cases
625
1,484
Observed-expected
83
83
SIR
1.133
1.056
95% of SIR
0.984 ∼ 1.134
1.017 ∼ 1.261
NPYSv/104 PYSv
2.758
4.833
EAR·104 PYSv
30.1
17.2
95% CI of EAR
3.9 ∼ 59.2
-5.0 ∼ 41.0h, mSv
1.694
1.151
0.47
ERR, %/mSv
7.8
4.9
7
95% CI of ERR in %/1mSv
1.0 ∼ 15.4
-1.4 ∼ 11.6
-27 ∼ 41
AR,%
11.7
5.3
95% CI of AR
1.5 ∼ 23.0
-1.6 ∼ 12.7

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For the assessment of data presented in Table 4, incidence rates in the childhood leukemia in theentire Belarus given in Table 2 were used. The expected incidence rate in the period 1986-1992 was thenassessed by combining noncorrected numbers of leukemia cases established for periods 1980-1985 and1993-2000 and respective person-years also presented in Table 2. Collective and mean individual doses of
the whole body irradiation presented in Table 1 were used for assessment of radiation risks given in thesecond and third columns of Table 4.
As can be seen from Table 4 the relative excess risk of 7.8% per mSv (95%CI from 1.0% to 15.4%
per mSv) was estimated for the period 1986-1992 for the entire Belarus on the basis of observed data. Thisvalue agrees very well with estimation of Auvinen et al [8] that found relative risk for Finnish children forthe period 1989-1992 equal to 7% per mSv (95%CI from –27% to 41%).

Comparison with other studies
The very good agreement in radiation risks established in the present report and study [8] gives anadditional evidence of a radiation origin of the short-time increase in the childhood leukemia manifested
after the accident at the Chernobyl NPP in Belarus and Finland.
It is clear that a very good agreement in radiation risks found in this report and by Auvinen et al [8]could not be achieved simply by chance. Two sets of data are used for estimation of radiation risks. One
set consists of data of medical statistical account. The second set consists of physical data such as
contamination and irradiation levels. All these sets of data are quite different in case of children of Finlandand children of Belarus. Therefore the existing agreement in radiation risks established in the present
report and by Auvinen et al [8] gives an evidence that increase in the childhood leukemia manifested in
Belarus and Finland is a result of irradiation caused by the Chernobyl NPP. The same conclusion can be
drawn in respect of findings [4-5,9].
It is known that the rejection of link between radiation and an increase in the leukemia by infants[4-5,6] and children [9] observed after the Chernobyl accident is mostly based on results of analysis of theleukemia in infants and children of Belarus [7,10-12]. No statistical significance of the increase inleukemia incidence as well as no correlation between the incidence and correlation between contaminationlevel was established in the reports [7,10-12]. However the reports [7,10-12] had significant methodical
shortages. In case of reports [10,11] incidences in leukemia registered before the accident at the Chernobyl
NPP were compared with data established in 1986-1992. The authors [10,12] could not find the statisticalsignificance in the increase in leukemia in 1986-1992. However, data registered in Belarus after the period
1986-1992 demonstrate a decreasing trend of spontaneous childhood leukemia to the incidence before theChernobyl accident.
An inappropriate method of analysis was used also in the report [12]. In this case the childhood
leukemia in children of Belarus was analyzed by comparing annual incidences. Moreover boys and girls
were analyzed separately. Such analysis was performed separately for different regions of Belarus. As aresult, the children’s population of Belarus was divided in the big number of subgroups. This splitting
excluded any possibility to find the increase in the childhood leukemia in Belarus.
The indicated shortages and the influence of demographic factors are reasons for decreasing
findings made in reports [7,10-12]. However, specialists in radiation protection concluded on the basis ofthese findings that there was no increase in infants and childhood leukemia in Belarus after the Chernobyl
accident at whole [13,14]. As a result, they concluded the increase in infants and children leukemia
observed in reports [4-6,9] had no any link to radiation.
Data established in the present report demonstrate that all these conclusions made in reports [13,14]
are incorrect. The statistical significant short-time increase in the leukemia incidence occurred after the- 160 -

Chernobyl accident in Belarus. The most probable reason of this increase is irradiation of Belarus as aresult of the Chernobyl accident. The same conclusion can be made in respect of the increase in theleukemia incidence observed in some countries of Europe [4-6,9].
It is to notice here that ecological method was used in the present report as well as in reports [4-1012,15-17] for analysis of the incidence in infants and children’s leukemia. This method has significant
limitations in interpreting of established results because both exposure and outcome are determined at thelevel group level. Therefore, ecological studies do not allow an assurance that the individuals who areexposed are actually those who develop the disease [35]. As a result of these limitations, ecological studies
have significant problems by answering a very important question about possible threshold in inducing of
the disease. For example, according to the assessment carried out in the report [36] doses of the wholebody irradiation of the Belarusian population caused by the Chernobyl accident are in the range from somefractions of millisievert up to some hundreds of millisievert. It is impossible to determine on the basis ofdata estimated for the Belarusian children in the presented report if there is a threshold in case of thechildhood leukemia.
Qualitative answer on the last question can give in case of the childhood leukemia ecologicalstudies carried out in range of lower doses.
The highest dose of the whole body irradiation accumulated by of Finland in the first 2 years after
the Chernobyl accident was 0.97 mSv [8]. It is known that irradiation dose of some small number of
persons (critical group) in any irradiated group is by 3-5 times higher than the arithmetic mean dose.
Assumption that radiation-induced leukemia in case of children of Finland developed in the critical groupindicates, that ionizing radiation can induce radiation-induced leukemia at least at doses of the whole body
irradiation in the range 3-5 mSv. This means that if the threshold exists in reality it can not be higher than
3-5 mSv in case of the childhood leukemia.
It was demonstrated in the previous section that radiation risk of the childhood leukemia in Belarus
agrees very well with radiation risk established for children of Finland [8]. It is also quite close toradiation risk found for inhabitants of Hiroshima and Nagasaki irradiated at the age 0-9 years [37].
According the authors [37] excessive relative risk of leukemia incidence in persons irradiated at the age 09 years and followed up to the age 20 years is 44/Sv. This corresponds to a relative risk of 4.4% per mSv.
This is a fully unexpected result. According the paradigm of radiation protection [38] radiation risk
depends on doses and dose rates of irradiation. It is well known that doses and doses rates of theBelarusian population differ very significantly from doses and dose rates of survived inhabitants ofHiroshima and Nagasaki. The main contribution to the whole body doses of the Belarusian population, as
can be seen from Table 1, gave irradiation in 1986-1989. In case of atomic bomb survivors the main
fraction of dose was delivered within 1 minute [39]. Individual dose of the whole body irradiation of theBelarusian children was by 2 orders in magnitude lower than population dose of the atomic bomb
survivors. The higher radiation risk of the incidence in leukemia in children of Belarus than in atomic
bomb survivors despite of such immense difference in irradiation doses gives the clear evidence that usingof the DRREF factor in case of chronic or protracted irradiation is not relevant at least in case of thechildhood leukemia.
Conclusions
The analysis of the childhood leukemia in Belarus carried out for the period 1980-2004 indicates that theaccident at the Chernobyl NPP caused manifestation of additional leikemias in the Belarusian children.
Their number is about 83 cases in the period 1986-1992. The excessive relative risk of leukemia assessed- 161 -

for this period is 7,8% per 1 mSv. This value agrees very well with radiation risk found after the
Chernobyl accident in Finland. Quite good agreement exists also of radiation risks estimated in this reportwith radiation risks established for atomic bomb survivors irradiated at the age 0-19 years. This is an
unexpected result because of very significant difference in temporal patterns of irradiation of theBelarusian children and atomic bomb survivors. The dose rates of irradiation of the whole body in case ofchildren of Belarus were approximately 1014 times lower than dose rates of atomic bomb survivors
irradiation. The population doses of the whole body irradiation of the Belarusian children were lower by
two orders in magnitude lower than in case of atomic bomb survivors. Despite these differences in doses
and dose rates radiation risks of the leukemia incidence in children of Belarus are by some factors higher
than in atomic bomb survivors. This indicates that the hypothesis about decrease of radiation risk withdecrease of doses and dose rates is not relevant at least in case of the childhood leukemia.
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