Iodine-131 Contamination, Thyroid Doses and Thyroid Cancer in theContaminated Areas of Russia
Valery F. STEPANENKO, Evgeny M. PARSHKOV, Viktor A. SOKOLOV, Mark Yu. ORLOV,
Alexander I. IVANNKOV, Valery G. SKVORTSOV, Elena K. IASKOVA,
Timofey V. KOLIZSHENKOV, Irina G. KRYUKOVA, Anatoly F. TSYB
Medical Radiological Research Center, Russian Academy of Medical Sciences, Korolev Str., 4, 249020,
Obninsk, Russia: valeri@obninsk.com

Abstract
About 1,800 PBq of I-131 was deposited in the environment as a result of the Chernobyl
accident. The most contaminated territories in Russia are located in Bryansk, Tula, Orel and Kaluga
regions. About 80% of total I-131 deposition was formed during the first week after the accident.
Direct measurements of deposition densities of I-131 were very limited as far as this radionuclide
decayed very fast (with half time about 8 days). In contrast, Cs-137, which is long-lived radionuclide,
was investigated much more extensive. As a result all available information about the ratio of I-131 to
Cs-137 has been used to estimate deposition densities of I-131 for the purpose of thyroid dose
estimation. The results of direct measurements of radioactive iodine content in human thyroid gland
together with the available data on I-131 and caesium-137 contamination of the soil were used fordevelopment of semi-empirical model for reconstruction of thyroid absorbed doses in cases when themeasurements were not performed in 1986.
According to the estimations, which are based on the results of direct measurements of I-131
activity in thyroid (Kaluga and Bryansk regions), the median of individual thyroid dose values in
Kaluga region (7 districts) varies from 30 mGy for children to 8 mGy for adults. In Bryansk region (5districts) the median dose values for adults are in the range from 140 mGy to 30 mGy. Collective
thyroid doses over the territories where the density of Cs-137 soil contamination exceeded 3.7 kBq/m2(0.1 Ci/km2) in the most contaminated 4 regions were estimated to be 72,600, 16,900, 13,400 and
3,400 person-Gy for Bryansk, Orel, Tula and Kaluga regions, respectively.
The data on annual thyroid cancer morbidity over 1986-2000 years in residents of the mostaffected Bryansk region, aged 0-50 years at the moment of the accident, is also presented. During thefirst five years after the accident (1986-1990) annual thyroid cancer morbidity in different age groups(0-4 years, 5-9, 10-14, etc.) remained at quite stable levels. Since 1991 a stable increase of the numberof thyroid cancer in all age groups of the studied population has started. The semi-empirical model
was applied to reconstruct individual thyroid dose for 26 thyroid cancer cases (0 - 18 years old at the
moment of the accident) in the most contaminated 4 districts of Bryansk region. The tendency of dose
dependence of thyroid cancer incidence was found.

IODINE-131 CONTAMINATION
In total about 1,800 PBq of I-131 was deposited in the environment as a result of the Chernobyl
accident [1]. The most contaminated territories in Russia are located in Bryansk, Tula, Orel and Kaluga
regions [2] (see Table 1).
Data on the radionuclide composition of fallout and atmospheric aerosol samples have been obtainedby the Institute of Experimental Meteorology (SPA “TYPHOON” now, Obninsk, Russia) [2]. The firstsoil samples near the Chernobyl NPP were collected on 30.04.86. The fallout and atmospheric aerosol
samples have been taken beginning on 27.04.86. The principal measurements of the isotopic compositionof environmental samples have been performed after 10.05.86. The basic body of soil samples, for which86Table 1. Population residing in the contaminated regions following the Chernobyl accident(Russia, 1991.01.01).
N

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Regions

Belgorod
Bryansk
Voronezh
KalugaKursk
Orel
St.-Petersburg
Lipetsk
RyasanTambov
Tula
Ul’yanovsk
Penza
Smolensk
Mordoviya
Total

Cs-137 soil
contamination:
37-185 kBq/m2(1-5 Ci/km2)
No ofPopusettlem.
lation
56
1940
829
227220
35
11940
289
78078
230
1341891987
326581
44
19591
149
38882
646
182000223569
1736
768773
9000
51000
10000
20000
1882763

Cs-137 soil
contamination:
185-555 kBq/m2(5-15 Ci/km2)
No ofPopusettlem.
lation288

147361

135

15492

64

17648

311

166776798

347277

Cs-137 soil
contamination:>555 kBq/m2(>15 Ci/km2)
No ofPopusettlem.
lation
275

93100

275

93100

Subtotal
No ofsettlem
56
1392
35
424
230
2051
44
149
646
22
2047

7096

Population
1940
46768111940
93570
13418934422919591
38882
1820003569
935549
9000
51000
10000
20000
2323140

the isotopic composition is known, was collected and measured in the second half of 1986 and during
1987, i.e. when iodine-131 activity was already negligible. As a result, direct measurements ofenvironmental iodine-131 are very scarce now.
To get detailed information on soil and atmospheric contamination by I-131 in the first period after
the Chernobyl accident, all available data were used on the isotopic composition of soil (43 points), fallout(14 points) and atmospheric aerosol samples (7 points) [3]. To verify the validity of estimating the isotopic
composition of soil, fallout and aerosol samples, the 134Cs/137Cs activity ratios were determined
simultaneously with 131I/137Cs activity ratios. The accuracy of the ratios for soil samples was estimated as
15-25%, for the fallout - as 20-30% and for aerosol - 30-50%. The 134Cs/137Cs ratio averaged for thereactor core during the Chernobyl accident is known to be 0.53 with a high accuracy of SD=0.02.
From the very beginning when plotting the fields of soil I-131 contamination, it was attempted toconnect this contamination with the density of soil contamination by Cs-137 (having a relatively long halflife, T1/2 = 30.2 years) for which the measurement data are maximum available. However, such a
description may be accepted only for rough estimates of I-131 activity. In fact, there were notabledifferences in the radionuclide composition of contamination due to the peculiarities of transfer ofradioactivity and to the variations of transfer directions in the atmosphere: the I-131 to Cs-137 activity
ratios did not exceed a value of 15 in Russia (from 4.4 to 15, at 1st of May 1986), whereas in someterritories of Belarussia these ratios were remarkable greater – from 5 to 42 on 1 of May 1986 [1,2].
Therefore, even if Cs-137 contamination levels were equal, the values of iodine radioisotopes intake could
be different for various regions.
To reconstruct the trajectories of radionuclide transfer in the first period after the accident, the data
were collected on wind velocity and direction at various heights above the sea level for the European
territory of the former USSR (ETU) and also precipitation data were collected between 230-380 E and 460560 N from the end of April to late May 1986 [3].
Using the trajectories analyses, the time of particle arrival to a given site, district or region for eachheight level was estimated [2]: the earliest time of arrival and the latest time of leaving of air particles
were determined for a given site or region (Tables 2-4) This time was considered as a probable period
during which a given territory was radioactively contaminated.
87

Table 2. Data on air particles transfer trajectories in Bryansk region (Russia).
Trajectory departure from Chernobyl - 27 - 29 April 1986
2
3
4
5
6
7
1
Bryansk
17/28 19/28
06/27
22.7
2
Dubrovka
21/28 00/29
03/27
no *
3
Dyatkovo
00/29 03/29
06/27
no *
4
Zhukovka
20/28 21/28
06/27
no
5
Kletnya
18/28 19/28
06/27
6
Zhiryatino
17/28 19/28
07/27
7
Karachev
17/28 19/28
09/27
1.3
8
Trubchevsk
23/29 01/30
03/27
4.0
9
Navlya14/28 16/28
09/27
no
20/29 22/29
03/27
no10 Pochep
12/28 14/28
09/27
5.7
11 Fokino
19/28 21/28
07/27
22.7
14/28 0.2 16/29 0.7
08/27
14/28 15/28
08/27
12 Komarichi
04/29 0.7 06/29 0.7
08/28
11/29 0.7 13/29 0.7
03/29
13 Suzemka
05/29 0.7 07/29 0.7
21/28
10/29 11/29
00/29
14 Klintsy
12/28 13/28
09/27
no *
15 Starodub
11/28 13/28
09/27
no16 Krasnaya Gora
14/28 15/28
07/27
no17 Mglin
17/29 21/29
03/27
no *
12/29 0.7 13/29 0.7
10/27
no18 Sevsk
04/29 0.7 05/29 0.7
18/28
no11/29 0.7 16/29 0.2
03/29
0.5
12/29 16/29
00/29
0.5
19 Lokot
14/28 15/28
11/27
20 Surazh
16/29 20/29
03/27
no
14/28 15/28
08/27
no21 Unecha
18/28 21/29
03/28
no22 Vigonichi
16/28 17/28
08/27
Explanation for columns 1-7:
1 - earliest date of the trajectory arrival, hour/day (hh/dd) and trajectory height above the sea level, km;
2 - latest date of the trajectory departure, hour/day (hh/dd) and trajectory height above the sea level, km;
3 - date of the air particles trajectory departure from the Chernobyl reactor, hour/day (hh/dd);
4 - precipitation, mm/day ( no - no precipitation, * - data related to the nearest settlement);
5 - earliest date of the trajectory arrival at the height 0.45 km above the sea level, hour/day (hh/dd) and latest date ofthis trajectory departure, hour/day (hh/dd);
6 - date of the 0.45 km air particles trajectory departure from the Chernobyl reactor, hour/day (hh/dd);
7 - precipitation, mm/day (no - no precipitation, * - data related to the nearest settlement);
N

Settlements

1

Table 3. Data on air particles transfer trajectories in Tula region (Russia).
N

Settlements

Trajectory departure from Chernobyl - 27 - 28 April 1986
2
3
4
5
6
01/29 02/29
19/27
06/29 09/29
08/27
03/29 05/29
09/27
02/29 04/29
10/27
05/29 07/29
06/27
02/29 0.2 11/29 0.7
18/27
no *
02/29 04/29
18/27
17/29 0.2 17/29 0.2
18/28
no *
05/29 0.2 10/29 0.7
12/27
08/29 0.7 10/29 0.7
00/28
01/29 0.2 09/29 0.7
15/27
no01/29 02/29
15/27
08/29 0.2 09/29 0.7
15/28
no22/28 23/28
12/27
01/29 03/29
09/27
07/29 08/29
06/27
03/29 06/29
09/27
23/28 0.2 14/29 0.7
18/27
23/28 01/29
18/27
13/29 0.7 14/29 0.7
18/29
1

1
2
3
4
5
6
7
8
9
10
11
12
13

Efremov
Novomoskovsk
Uzlovaya
Bogoroditsk
Klimovsk
KurkinoKurkinoEpifanEpifanVolovoVolovoChern
Plavsk
Schekino
Kireevsk
Arkhangelskoye
Arkhangelskoye

Explanations for columns 1-7 are shown in Table 2.

88

7
no
1.7 *
1.7
no
1.7 *
no *
no
1.6
0.3
no *
no *
-

Table 4. Data on air particles transfer trajectories in Kaluga region (Russia).
N

Settlements
1

1
2
3
4
5

Lyudinovo
ZhizdraDuminichi
Khvastovichi
Ul’yanovo-

Trajectory departure from Chernobyl - 27- 28 April 1986
2
3
4
5
6
02/29 04/29
06/27
23/28 01/29
06/27
23/28 01/29
06/27
20/28 22/28
06/27
03/29 06/29
06/27

7
no*
no
no*
0.7*
no*

Density of I-131 activity on the soil, kBq/sq.m

Density of I-131 activity on the soil, kBq/sq.m

Explanations for columns 1-7 are shown in Table 2.

Gomel (Belorussia)
3

10

Kiev (Ukraine)2

10

Minsk (Belorussia)

101
Obninsk (Russia)

100

10-1
2

4

6

8

10

12

14

16

18

20

Days after the accident
Fig. 1. Accumulation of I-131 activity in soil.

103

Pinsk (Belorussia)
Baltiysk (Russia)

Klaipeda (Lithuania)

102

Mogilev (Belorussia)
Poltava (Ukraine)

101

Donetsk (Ukraine)

Izmail (Ukraine)

100

10-1
5

10

15

20

Days after the accident
Fig. 2. Accumulation of I-131 activity in soil.

As noted above, the data on the results of direct measurements of radioactive iodine isotopes in theenvironment after the Chernobyl accident are scarce: for example the time dependences of I-131 fallout
are known only for a few location over all territory of FSU [2-5]. The time integration of such kind of
dependencies show that a major part (more than 80-90 %) of I-131 contamination was accumulated instudied territories by the moment D + 5 days (Fig.1,2). These data are confirmed by analyzing the dose
rate dependence on time at some settlements. For example, in Novozybkov (Bryansk region, Russia) as
well as in Chernobyl (Ukraine), Pinsk (Belorussia) and Semenovka (Ukraine), the dose rate trend on timeshows that a dose rate had increased only during the radioactive cloud passage, i.e. prior to D+5[2,4].
After the cloud passage the dose rate had rapidly decreased.
Despite the shortage of the available data with the results of I-131 measurements, this information isvery valuable because the knowledge of I-131/Cs-137 ratios and time parameters of fallout are very
important for thyroid dose estimations.
THYROID DOSES
Intake of radioactive iodine isotopes, mainly I-131 in milk, was the main source of thyroid irradiationof population in contaminated settlements. The results of direct measurements of radioactive iodine
content in human thyroid gland in Byelorussia together with available data on I-131 and Cs-137
contamination of the soil were used for development of semi-empirical model for reconstruction of thyroid
absorbed doses in cases when the measurements were not performed in 1986 [2]. For validation andtuning of this model in Russian territories about 30,000 direct measurements of radioactive iodine content

89

in human thyroid gland in Kaluga and Bryansk regions (Russia) [6] and all available data on I-131 and Cs137 contamination of the soil [4,5] were used.
Dose estimation by semi-empirical model
Mean dose values in exposed population of each contaminated settlement over Russia where thedensity of Cs-137 soil contamination exceeded 3.7 kBq/m2 (0.1 Ci/km2) were evaluated using the model.
Collective doses for contaminated “spots” in 4 most contaminated Russian regions were estimated as thefollowing [2]: 72,600 person-Gy for Bryansk region (in population of 1,137,100 persons), 16,900 personGy for Orel region (in population of 448,000 persons), 13,400 person-Gy for Tula region (in population of
1,310,000 persons) and 3,400 person-Gy in Kaluga region (in population of 213,500 persons) (see Table 5
and Table 6).
Dose estimation based on direct measurement data
According to the estimations (Table 7), which are based on the results of direct measurements of I131 activity in thyroid gland in the inhabitants of the contaminated district in Kaluga and Bryansk regions[6], the median of individual thyroid dose values in Kaluga region (7 districts) varies from 30 mGy forchildren to 8 mGy for adults (geometric standard deviation of about 2.6). As seen in Table 8, in Bryansk
region (5 districts) the median dose values for adults are in the range from 140 mGy to 30 mGy (geometricstandard deviation of about 2.7).
THYROID CANCER
Annual thyroid cancer morbidity over 1986-2000 years in residents of the most affected Bryansk
region, aged 0-50 years at the moment of the accident, is presented in Table 9-11.
All thyroid cancer cases (in total 1201 cases) in patients aged 0–50 years at the period of iodine
radionuclides action (May-June 1986), which were registered in the Bryansk Regional oncological registry,
were taken as the basic material for analysis. Age limit in 50 years is explained mainly by low life span of
Russian population (around 70 years for females and 60 for males). We believe, that the used age period(0–50 years at the moment of the accident and correspondingly 0–65 years at the moment of diagnosis) islarge enough for elucidation of the general features of the post-Chernobyl thyroid cancer situation. Annual
thyroid cancer morbidity was followed up in this cohort of population since 1986 to 2000 and summarized
over 5-year periods (1986-1990, 1991-1995, 1996-2000) in different age groups (0-4 years, 5-0, 10-14,etc.). Such division permitted to form comparable subgroups for both sex ans age over all period ofsurveillance.
Average number of Bryansk region population in the age cohort 0-50 years at the moment of theaccident (and correspondingly in the next 5-year periods) comprised approximately 1 million and in eachage group around 100,000 (Table 9). Only in the age group 40-44 year (period 1986-1990), whichcorresponds to 45-49 year (period 1991-1995) and 50-54 year (period 1996-2000), there is a demographic
fall as a consequence of the World War II. It should be noted that the number of the total examined cohort
as well as the numbers of population in individual subgroups did not markedly change during theanalyzing period. This permitted to carry out a correct analysis of thyroid cancer morbidity in age groups.
Table 10 demonstrates annual distribution of thyroid cancer cases in patients aged 0-50 at the
moment of the accident (Bryansk cohort, 0-64 years old at diagnosis, both sexes). Table 11 presents
thyroid cancer incidence rate in the same cohort averaged over five years periods after the accident.
Table 10 and Table 11 demonstrate that during the first five years after the accident (1986-1990)
annual thyroid cancer morbidity in different age groups (0-4 years, 5-9, 10-14, etc.) remained at quite
stable levels. Since 1991 a stable increase of the number of thyroid cancers in all age groups of the studied
population has started. It’s seems to be that the minimal duration of the latent period of radiogenic thyroid
90

Table 5. Thyroid doses : Bryansk and Tula regions, Russia.
Cs-137 soil
contaminat. density,
kBq/m2BRYANSK
3.7- 37
37 - 185
185 - 555
>555
Total
TULA
3.7- 37
37 - 185
185 - 555
Total

Population,(×103 pers.)

Average Cs-137
soil contaminat.
density, kBq/m2

Average thyroid
dose in population,mGy *Collective dose inpopulation,(×103 person-Gy) *

670
227
147
93.1
1137.1

12.6
86.6
336
918

9.5
58.9
176
289
64

6.39
13.4
25.9
26.9
72.6

370
770
170
1310

24.4
112
281

4.43
11.2
18.3
10.2

1.64
8.64
3.11
13.39

* - Taking into account the real beginning of the pasture period.

Table 6. Thyroid doses: Kaluga and Orel regions, Russia.
Cs-137 soil
contaminat.
density, kBq/m2
KALUGA
3.7- 37
37 - 185
185 - 555
Total
OREL
3.7- 37
37 - 185
185 - 555
Total

Population, (×103
pers.)

Average Cs-137 soil
contaminat. density,
kBq/m2Average thyroid
dose in population,mGy *)

Collective dose inpopulation, (×103
person-Gy) *

120
78
15.5
213.5

20.3
98.4
263

9.50
21.9
35.5
15.9

1.14
1.71
0.55
3.40

100
330
18
448

23.3
90.3
220

17.3
42.0
72.7
37.7

1.73
13.85
1.31
16.9

* - Taking into account the real beginning of the pasture period.

Table 7. Estimated parameters of individual thyroid dose distribution (7 investigated districtsof Kaluga region).
ItemsaN
MID(mGy)
DA (mGy)
SD (mGy)
DM (mGy)
GSD

Groups by age at the time of the accidentb
1-2
2-7
7-12
12-17
989
7491
6440
4997
530
460
320
250
43
23
15
14
52
29
17
17
26
14
10
8.3
2.7
2.6
2.4
2.7

-1
1075
550
52
58
31
2.7

175732
250
13
15
8.1
2.7

a

: N=number of persons with the results of direct measurements in given age range; MID=maximum individual dose;
DA=arithmetic mean dose; SD=standard deviation; DM=median dose; GSD=geometric standard deviation.
b:Include the left end while exclude the right end.

Table 8. Estimated parameters of individual thyroid dose distribution (five investigateddistricts of Bryansk region).
District
Gordeevskiy
Klimovskiy
Klintsovskiy
Krasnogorskiy
Novozybkovskiy

Arithmetic mean dose
(mGy)
120
48
62
223
46

a

Geometric standard deviation is 2.7.

91

Median dose (mGy)a

Number of adults

74
31
41
143
30

75
9
10
93
83

Table 9. Average size of cohort and number of persons in different age groups in 5-year periods.
(Bryansk cohort, 0-50 years old at the moment of the accident, both sexes)
Number of population in different age groups (persons)Totalnumber of
populationin cohort

0–4

5–9

10 – 1415 – 19

20 – 24

25 – 29

30 – 34

35 – 39

40 – 4445 – 49

50-54

55-59

1986-1990

988315.4110431.8

103914.4

100992.8

95863.894283.0114403.4

115018.0

102798.2

64859.2

85750.8++

1991-1995

974626.8-111004.4

104406.898640.4

88211.2

95248.8116310.2

113623.8

100113.4

59952.8

87115.0+

1996-2000

982553.7--

114588.0104153.3

96770.089934.3

102560.0121572.0

111663.796125.051610.3

93577.0

Years

Notes: 1. Sign (-) means the shift-out of cohort after 5-year periods.
2. Sign (+) means that age groups 0-49 analyzed in period 1986-1990 entered in the age groups 5-54 in period 1991-1995 and the age groups 10-59 in period 1996-2000.

Table 11. Thyroid cancer incidence rate at diagnosis in persons aged 0–50 years at the moment of the Chernobyl accident avareged over 5 years periods
after the accident. ( Bryansk cohort, both sexes, per 100 000 of population)
Year ofdiagnosis

Number of thyroid cancer cases in different age groups
0-4

5-9

10-14

15-19

20-24

25-29

30-34

35-39

40-44

45-49

50-54

55-59

60-64

1986-1990

0

0

1.9

2.1

6.4

15.7

26.1

35.0

37.0

29.2

27.3

+

+

1991-1995

-

6.5

14.6

17.5

21.9

27.7

35.4

58.2

70.3

74.1

57.2

49.7

+

1996-2000

-

-

19.2

30.6

28.1

35.6

37.5

70.6

87.8

133.3

116.8

74.7

63.0

Notes:
Sign ( - ) means the absence of patients in the corresponding age groups owing to their natural shift in elder age groups.
Sign ( + ) means the absence of patients in the corresponding age groups owing to restriction of the analyzing cohort by the of age 50 years old at the moment of the accident.

92

Table 10. Annual distribution of thyroid cancer cases in patients aged 0-50 at the moment of accident.
(Bryansk cohort, 0-64 years old at the moment of diagnosis, both sexes)
Number of thyroid cancer cases in different age groups
Year ofdiagnosis

1986
1987
1988
1989
1990
Sub total
1986-1990
1991
1992
1993
1994
1995
Sub total
1991-1995
1996
1997
1998
1999
2000
Sub total
1996-2000
Total
1986-2000

0-4

5-9

10-14

15-19

20-24

0
0
0
0
0

0
0
0
0
0

0
1
0
0
1

0
1
0
0
1

1
1
1
3
0

Sub
total
0-24
1
3
1
3
2

25-29

30-34

35-39

40-44

45-49

4
4
5
3
2

5
5
5
10
5

4
6
10
7
9

1
5
5
6
7

2
7
4
6
6

Sub
total
25-49
16
27
29
32
29

0

0

2

2

6

10

18

30

36

24

25

-

1
3
1
2
-

0
0
0
7
8

2
0
5
7
3

1
4
3
5
7

4
7
9
21
18

8
3
6
4
8

6
8
10
7
10

8
7
15
18
15

7
16
11
7
17

-

7

15

17

20

59

29

41

63

-

-

3
7
7
2
2

3
3
5
10
10

2
6
2
8
8

8
16
14
20
20

5
5
4
9
10

5
8
4
13
11

-

-

21

31

26

78

33

0

7

38

50

52

147

80

50-54

55-59

60-64

Total
0-64

4
2
7
6
7

+
+
+
+
+

+
+
+
+
+

21
32
37
41
38

133

26

+

+

169

5
6
11
16
16

34
40
53
52
66

13
12
8
12
6

+
3
13
10
14

+
+
+
+
+

51
62
83
95
104

58

54

245

51

40

+

395

6
17
17
14
29

14
15
13
22
29

14
18
17
29
26

44
63
55
87
105

7
8
9
28
29

16
10
11
20
8

3
12
8
15
21

78
109
97
170
183

41

83

93

104

354

81

65

59

637

112

182

175

183

732

158

105

59

1201

Notes:
1. In shaded lines and columns the summarized data over time intervals and age groups are presented.
2. Sign ( - ) means the absence of patients in the corresponding age groups owing to their natural shift in elder age groups.
3. Sign (+) means the absence of patients in the corresponding age groups owing to restriction of the analyzing cohort under 50 years old at the moment of the accident.

93

cancer is equal abut 5 years. After that we can see the rise of thyroid cancer morbidity in all age groups
due to possible influence of the Chernobyl accident.
One of the key questions regarding the radiogenic nature of thyroid cancer following the Chernobyl
accident was focused on its dose dependence of the thyroid cancer incidence. There was an attempt toinvestigate this question using the available individual data for 26 thyroid cancer cases in Bryansk region.
The retrospective individual dose estimations were performed for 26 thyroid cancer cases (17 female
and 9 male cases in the age 0-18 years old at the moment of accident) [7] which had been registered before
the end of 1997 in Novozybkovsky, Krasnogorsky, Klintsovsky and Klimovsky districts – the four of themost contaminated territories of Bryansk region. The verification of diagnosis in 18 cases was performed
by a group of experts at an international level: Prof. D. Williams (Cambridge, UK), Prof. E. Lushnikov(Obninsk, Russia ), Prof. G. Frank (Moscow), Dr A. Abrosimov (Obninsk). Other cases were diagnosed
and operated in Children Oncology Research Institute of Oncological Scientific Centre (Moscow).
A special questionnaire was used to gather data for individual thyroid dose reconstruction, including
information about milk consumption, leafy vegetable consumption, and use of thyroid blocking agents.
Individual doses were retrospectively estimated using semi- empirical model [2]. In Table 12 thereconstructed individual thyroid doses are presented for different dose ranges: < 0.25 Gy, 0.25 Gy ≤ 0.5
Gy, 0.5 Gy ≤ 0.75 Gy, 0.75 Gy ≤ 1.0 Gy and ≥ 1.0 Gy.
The results of analysis of available individual dose estimates based on thyroid counting todetermine I-131 content in May-June 1986 were applied in order to estimate the numbers of young
population related to various individual dose ranges [6]. Then, the numbers of thyroid cancer cases
corresponding to the different individual dose ranges were referred to the young population of the same
dose ranges (Table 12).
The “background” level of thyroid cancers for the investigated population during 11.7 years after theaccident was taken into account. For calculation of the background level the statistical data of [8] wereused. The results of dose dependence estimation are presented in Table 12 and in Figure 3.
CONCLUSIONS- The most contaminated territories in Russia following the Chernobyl accident are located in
Bryansk, Tula, Orel and Kaluga regions. According to the trajectory analysis of the radioactive plumes
from Chernobyl, the main part (more than 80-90 %) of I-131 contamination in these regions was formedby the five days after the accident. There were notable differences in the radionuclide composition ofcontamination due to the peculiarities of transfer of radioactivity and to the variations transfer directions inatmosphere: the I-131 to Cs-137 activity ratios did not exceed value of 15 in Russia, whereas in the someterritories of Byelorussia these ratios were remarkable greater than 15.
Table 12. Estimation of thyroid cancer incidence dose dependence for population in fourcontaminated districts of Bryansk region (age group < 18 years old at the moment ofaccident); see Figure 3 as well.
Number of “Background”
thyroidlevel of thyroid
cancer cases cancers for thein the dose
population inrange
the dose range

Standard
Incidence of thyroid
Thyroid dosedeviation ofcancer cases in thein cancer
thyroid dose indose range per 104
cases,
cancer cases,
Gy,( D )persons
Gy

Range ofindividual
thyroiddoses,
Gy

Populationin the dose
range,
persons

<0.25

29316

8

1.53

0.073

0.069

2.21

0.25≤0.5

14439

5

0.752

0.32

0.096

2.94

0.5≤0.75

9294

6

0.484

0.67

0.043

5.93

0.75≤1.0

2654

3

0.138

0.87

0.095

10.1

≥1.0

2960

4

0.154

1.25

0.27

13.0

94

TH YR O ID C AN C SER IN C ID EN C E AB O VE B AC K G R O U N D
PER 1 0 0 0 0 P ER SO N S

I

16
14
12
10
8
6
4
2
0

0 ,0

0 ,2

0 ,4

0 ,6

0 ,8

1 ,0

1 ,2

1 ,4

1 ,6

D

TH YR O ID D O SE, G yFig.
F ig.31. . TH Y R O ID C AN C E R IN C ID E N C E V S IN D IV ID U AL TH Y R O ID D O SE S
fo u r districts o f B ryansk regio n: 2 6 cases fro m 0 4 .1 9 8 6 till 1 2 .1 9 9 7 ).
O nly perso ns o f 1 8 years o ld by 0 4 - 0 5 .1 9 8 6 .
U pper and lo w er cu rves are 9 5 % co nfidence bands.
See Table 3 and relatio nship (1 ), (2 ) as w ell.

- The results of direct measurements of radioactive iodine content in human thyroid gland in
Byelorussia as well as the available data on iodine-131 and Cs-137 contamination of the soil were used fordevelopment of semi-empirical model to reconstruct thyroid absorbed doses. For validation and tuning of
this model in Russian territories about 30,000 direct measurements of radioactive iodine content in human
thyroid gland in Kaluga and Bryansk regions (Russia) and all available data on I-131 and Cs-137
contamination of the soil were used.
- By using semi-empirical model mean thyroid dose values in exposed population of eachcontaminated settlement over Russia where the density of Cs-137 soil contamination exceeded 3.7 kBq/m2(0.1 Ci/km2) were evaluated. Collective doses for contaminated “spots” in the most contaminated 4
regions were estimated as the following: 72,600 person-Gy for Bryansk region (in population of 1,137,100
persons), 16,900 person-Gy for Orel region (in population of 448,000 persons), 13,400 person-Gy for Tularegion (in population of 1,310,000 persons) and 3,400 person-Gy in Kaluga region (in population of
213,500 persons).
- According to the estimations, which are based on the results of direct measurements of I-131
activity in thyroid (Kaluga and Bryansk regions), the median of individual thyroid dose values in Kaluga
region (7 districts) varies from 30 mGy for children to 8 mGy for adults (geometric standard deviation of
about 2.6). In Bryansk region (5 districts) the median dose values for adults are in the range from 140
mGy to 30 mGy (geometric standard deviation of about 2.7).
- The data on annual thyroid cancer morbidity over 1986-2000 years in residents of the most affected
Bryansk region is presented in different age groups. During the first five years after the accident (19861990) annual thyroid cancer morbidity remained at quite stable levels. Since 1991 a stable increase of thenumber of thyroid cancers in all age groups of the studied population has started as a possible result ofradiogenic influence of the accidental release of I-131 from the Chernobyl NPP.
- The semi-empirical model was applied to reconstruct individual thyroid doses for 26 thyroid cancer
cases (0 - 18 years old at the moment of accident) in the most contaminated 4 districts of Bryansk region.
A special questionnaire was used to gather data for individual thyroid dose reconstruction, including
information about milk consumption, leafy vegetable consumption, and use of thyroid blocking agents.
The incidence rate of thyroid cancer cases corresponding to the different individual dose ranges were
calculated by referring the number of thyroid cancer case to the young population of the same dose ranges.
The tendency of dose dependence of thyroid cancer incidence was found.

95

Acknowledgements
This work was supported in part by Russian Ministry of Health and by Russian Academy of Medical
Sciences. This work has been supported in part by Grant N N00014-94-1-0049 issued to Georgetown
University from the Office of Naval Research in support of the International Consortium for Research on
the Health Effects of Radiation. The contents are solely the responsibility of the authors and do notnecessarily reflect the views of the Office of Naval Research or Georgetown University. A part of thiswork was supported by Hiroshima University, Japan (special gratitude to Prof. M. Hoshi). Special
gratitude to the Ministry of Education (Japan) and to Dr. T. Imanaka (Research Reactor Institute of Kyoto
University, Japan) for the possibility to publish this paper. Authors are very grateful to Dr. P. Voilleque,
MJP Risk Assessment, USA, for very useful discussion and comments to the materials and data of thispaper.
References.
1. UNSCEAR 2000 Report to the General Assembly. Annex J: Exposured and Effects of the Chernobyl Accident.
In: International Journal of Radiation Medicine. Special Issue. Vol. 2-4 (6-8). 2000. Kiev. P. 3-109.
2. Stepanenko V.F., Tsyb A.F., Parshkov E.M. et al. Retrospective thyroid absorbed doses estimation in Russia
following the Chernobyl accident: progress and application to dosimetrical ecaluation of childhood thyroid
cancer morbidity. In: “Effects of low-level radiation for residents near Semipalatinsk nuclear test site”. Proc. of
the Second Hiroshima International Symposium, Hiroshima, July 23-25, 1996 (Edited by M. Hoshi, J. Takada, R.
Kim, Y. Nitta). Hiroshima University, 1996, p. 31-84.
3. Environmental Radioactive contamination after Chernobyl NPP Accident. IEM SPA “Typhoon”. Obninsk. p.305,
1986 (in Russian).
4. Orlov M.Yu., Snykov V.P., Khvalensky Yu.A. et. al. Radioactive contamination of Belorussia and Russia
territories after the Chernobyl accident. Atomnaya Energiya. 72:4. p. 371-376, 1992 (in Russian).
5. Makhonko K.P., Kozlova E.G., Volokitin A.A. Radioiodine accumulation on soil and reconstruction of doses
from iodine exposure on the territory contaminated after the Chernobyl accident. In: Radiation and risk, Bulletinof the National Radiation and Epidemiological Registry. English translation of Russian issue N7. Cambridge,
MA; 1997. p. 90-142.
6. Stepanenko V.F., Gavrilin Yu.I., Khrouch V.T. et al. Re-evaluation of thyroid doses in Russia after the Chernobyl
Accident. In: International Congress Series. Elsevier Science. 642 ,2001 (in press).
7. Stepanenko V., Tsyb A., Skvortsov V. et al. New results of thyroid retrospective dosimetry in Russia following
the Chernobyl accident. In: “Radiation and thyroid cancer”. (Eds.: G. Thomas, A. Karaoglou, E.D. Williams).
World Scientific Publishing Co.Pte. Ltd. Singapore-New Jersey-London-Hong-Kong. 1999, p. 333-338.
8. Dvorin VV, Axel EA, Trapesnikov NN. The statistics of malignant neoplasams in Russia and CIS. Moscow,
1995 (in Russian).

96