Re-evaluation of thyroid doses in Russia after the Chernobyl accident

International Congress Series 1234 (2002) 321 – 328

Re-evaluation of thyroid doses in Russia after the Chernobyl accident Valery F. Stepanenko a,*, Yuri I. Gavrilin b, Valery T. Khrouch b, Sergey M. Shinkarev b, Masaharu Hoshi c, Elena K. Iaskova a, Alexey E. Kondrashov a, Dmitry V. Petin a, Lev I. Moskovko a, Jun Takada c, Valery G. Skvortsov a, Mark Yu. Orlov a, Alexander I. Ivannikov a, Nataly M. Ermakova a, Anatoly F. Tsyb a, Anatoly D. Proshin d, Nikolay B. Rivkind d a

Medical Radiological Research Center, Russian Academy of Medical Sciences, 4 Korolev str., Obninsk 249020, Russia b State Research Center of Russia, Institute of Biophysics, Ministry of Public Health, Moscow, Russia c Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan d Bryansk Regional Diagnostic Center, Ministry of Public Health, Bryansk, Russia

Abstract Immediately after the Chernobyl accident, the team of Medical Radiological Research Center (MRRC) specialists carried out wide-scale measurements of iodine-131 content in the thyroid gland of 27 887 inhabitants of the Kaluga region. This initial information was presented only as official reports to governmental structures. Similar work was done by local specialists for 1441 inhabitants of the Bryansk region. The data of direct measurements provided us the basis for further individual thyroid dose estimations, where we exploited the developed model and personal interviews. This paper presents the results of updated dose evaluations, including the additional factors, such as dynamics of fallout and data on the pasture period. According to new estimations, the median of individual dose values in the Kaluga database (seven districts) vary from 30 mGy for children to 8 mGy for adults (geometric standard deviation of about 2.6). In the database of Bryansk (five raions), the median dose values are ranging from 140 mGy for children to 30 mGy for adults (geometric standard deviation of about 2.7). The obtained data were used for the validation of the semi-empirical model for thyroid dose reconstruction. This allowed the reconstruction of the mean doses for the settlements where I-131 measurements were not performed. The collective thyroid doses for the

*

Corresponding author. Fax: +7-8439-53390. E-mail address: [email protected] (V.F. Stepanenko).

0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 6 2 1 - 5

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Bryansk and Kaluga regions were estimated as 72 600 and 3400 persons-Gy (for population of 1137 100 and 213 500 inhabitants). D 2002 Elsevier Science B.V. All rights reserved. Keywords: Chernobyl accident; I-131; Thyroid dose; Individual dosimetry

1. Introduction Iodine-131 is the main factor of internal irradiation of the thyroid gland in the population that inhabited the contaminated Russian territories on April – May 1986 [1]. The thyroid dose estimations in contaminated settlements of the Kaluga and Bryansk regions started in May 1986, in order to provide information for the evaluation of the possible consequences of the Chernobyl accident [2]. The team of Medical Radiological Research Center, Russian Academy of Medical Sciences (MRRC RAMS) specialists carried out wide-scale measurements of iodine-131 content in the thyroid gland of 27 887 inhabitants of the Kaluga region [3]. Initial data were reported only to governmental structures as official report. Similar work was done for 1441 inhabitants of the Bryansk region by local specialists. Now, these data became very important for medical care and epidemiological studies of the thyroid cancer cases following the Chernobyl accident. Thyroid dose calculations in 1986 were based on the results of direct measurements of I-131 content in the thyroid and on the data of personal interviews, excluding data on prolonged fallout and the dates of the pasture period. Our further thyroid dose re-evaluations were performed in 1996, taking into account the recently published data concerning the time dependence of fallout and the dates of the pasture period. The results of this re-evaluation were reported only to the Ministry of Public Health of Russia [4]. The paper presents the main results of the updated thyroid dose evaluations.

2. Material and methods The measurements of iodine-131 content in the thyroid gland of 27 887 inhabitants of the contaminated Kaluga region were performed by specialists of MRRC RAMS during the period from 18 to 30 May 1986 in seven raions [3]: Khvastovichskiy (102 kBq/m2 of caesium-137 ground deposition density), Zhsizdrinskiy (129 kBq/m2), Ulianovskiy (191 kBq/m2), Lyudinovskiy (102 kBq/m2), Kuibishevskiy (39 kBq/m2), Duminicheskiy (75 kBq/m2), and Kozelskiy (41 kBq/m2). Because of the lack of special equipment, all thyroid measurements were done by means of very simple instruments with analogue output in exposure rates: SRP-68-01 with NaI(Tl) scintillation detectors without collimator. As a rule, two measurements for each person were performed: first, close to the thyroid gland, and second, close to the abdomen area (near the liver). The second measurement was selected in order to evaluate the caesium-137 input readings from the thyroid. The calibration of the instruments was verified before, during, and after the entire measurement campaign. The minimum I-131 activity in the thyroid that could be detected by this device

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is in the range of 1– 2 kBq (dependent on the age of the subject). Detailed description of the measurements is presented in Refs. [3 –5]. The measurements of iodine-131 content in the thyroid gland of 1441 inhabitants of the contaminated Bryansk region were performed by specialists of the Bryansk regional Oncological Hospital during May and June 1986. The results of the measurements, which are available in our database, are related to the following five districts and for Bryansk city [4]: Gordeevskiy (510 kBq/m2 of Cs-137 ground deposition density), Krasnogorskiy (535 kBq/m2), Novozybkovskiy (736 kBq/m2), Klintsovskiy (343 kBq/m2), and Klimovskiy (200 kBq/m2). The measurements were done by ‘‘GAMMA’’ equipment (Hungary) with scintillation NaI(Tl) probe supplied by lead collimator. All measurements were performed in integral mode with discrimination of the low gamma energy component. Therefore, two measurements had been done: first, over the thyroid gland, and second, over the hip area. The second measurement was selected in order to evaluate the caesium-137 input readings from the thyroid. The calibration of the equipment was done everyday using adult neck phantom and 20-ml solution with standard iodine-131 activity. Detailed description of the measurements is presented in Refs. [4,5]. The results of the direct measurements of I-131 thyroid content were used as the basis for individual thyroid dose estimations. The obtained thyroid measurements gave information related to the thyroid dose rate at the time of the measurement. In order to estimate the individual thyroid dose, it is necessary to have information on the dynamics of I-131 intake before and after the measurement. Only relative information is needed because the thyroid measurement provides a point of reference upon which the activity in the thyroid can be ‘‘tuned’’. For such kind of individual dose calculation, the model of dynamics of I-131 intake was used. This model provided dose calculations, taking into account the age, the moment of beginning and ceasing of the person’s stay in the contaminated territories, food consumption peculiarities (milk and leafy vegetables, including the date of the consumption stop), respiratory uptake, dynamics of prolonged I-131 fallout, and dates of the beginning of the local pasture period. The description of this model is presented in Refs. [3– 5]. The dates of the beginning of the local pasture period were provided in 1996 by the specialists of the Institute of Agriculture Radiology [4,5]. The dynamics of the prolonged I-131 fallout was adopted according to the recently published data [6]: as in Obninsk town (Kaluga region) for Kaluga’s districts and as in Gomel city for the southwestern districts in the Bryansk region. For the individual thyroid dose estimation, the results of questioning during the course of the measurements were used as well. The interviews included the questions concerning: age at the moment of accident, address, locations from the moment of accident till the moment of the measurement, consumption and origin of the milk and leafy vegetables including stopping of this consumption, stable iodine prophylaxis.

3. Results The individual thyroid doses were estimated for 26 724 persons from seven districts of the Kaluga region (Kaluga’s database) and for 891 persons from five districts of the Bryansk region (Bryansk’s database). Dose estimations were performed only for persons

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Table 1 Estimated parameters of individual thyroid dose distribution in the Khvastovichskiy district of the Kaluga region (102 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

150 300 56 59 36 2.5

159 340 42 44 28 2.5

906 310 28 29 19 2.3

996 230 18 18 13 2.3

1006 120 15 14 11 2.3

3183 250 16 17 10 2.6

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

Table 2 Estimated parameters of individual thyroid dose distribution in the Zhizdrinskiy district of the Kaluga region (129 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

153 550 110 81 85 2.0

117 350 78 62 57 2.2

646 430 48 43 34 2.2

549 200 29 25 20 2.4

620 180 24 24 15 2.6

609 110 15 15 9.6 2.6

a

N = number of records; 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 3 Estimated parameters of individual thyroid dose distribution in the Ulianovskiy district of the Kaluga region (191 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

144 520 80 66 60 2.1

157 530 88 83 62 2.3

780 460 56 50 42 2.2

802 320 29 28 22 2.2

705 250 26 27 18 2.4

265 140 21 21 15 2.3

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

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Table 4 Estimated parameters of individual thyroid dose distribution in the Lyudinovskiy district of the Kaluga region (102 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

283 200 38 31 30 2.0

233 100 25 18 20 1.9

2631 130 14 11 12 1.8

1331 100 12 8.4 11 1.7

587 120 9.3 8.1 7.5 1.9

559 54 8.7 6.6 7.0 1.9

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

Table 5 Estimated parameters of individual thyroid dose distribution in the Kuibishevskiy district of the Kaluga region (39 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

104 140 23 23 13 3.0

65 78 24 17 20 1.8

658 76 15 11 12 1.9

694 50 11 7.1 9.1 1.8

558 48 8.8 6.6 7.2 1.9

179 36 7.2 5.9 5.4 2.1

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

Table 6 Estimated parameters of individual thyroid dose distribution in the Duminicheskiy district of the Kaluga region (75 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

173 170 31 28 23 2.2

154 130 25 18 20 2.0

926 170 17 15 14 2.0

1097 110 12 11 9.4 2.0

720 54 9.8 8.3 7.5 2.1

451 85 8.9 9.0 6.3 2.3

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

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Table 7 Estimated parameters of individual thyroid dose distribution in the Kozelskiy district of the Kaluga region (41 kBq/m2 of Cs-137 ground deposition density) Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

68 80 12 14 6.3 3.0

104 82 12 11 8.1 2.4

944 89 6.4 6.5 4.6 2.3

971 56 4.3 4.0 3.6 1.8

801 45 3.0 3.3 2.5 1.9

486 27 2.4 2.6 1.9 2.0

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

Table 8 Estimated parameters of individual thyroid dose distribution in all the seven investigated districts of the Kaluga region Itemsa

N MID (mGy) DA (mGy) SD (mGy) DM (mGy) GSD

Groups by age at the time of the accidentb Below 1

1–2

2–7

7 – 12

12 – 17

17 above

1075 550 52 58 31 2.7

989 530 43 52 26 2.7

7491 460 23 29 14 2.6

6440 320 15 17 10 2.4

4997 250 14 17 8.3 2.7

5732 250 13 15 8.1 2.7

a N = number of records; MID = maximum individual dose; DA = arithmetic mean dose; SD = standard deviation; DM = median dose; GSD = geometric standard deviation. b Including the left end while excluding the right end.

Table 9 Estimated parameters of individual thyroid dose distribution in the five investigated districts of the Bryansk region District

Arithmetic mean dose (mGy)

Median dose (mGy)a

Number of adults

Gordeevskiy Klimovskiy Klintsovskiy Krasnogorskiy Novozybkovskiy

120 48 62 223 46

74 31 41 143 30

75 9 10 93 83

a

Geometric standard deviation is 2.7.

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with available personal information (at least age, address, and location). It should be noted that there were no countermeasures for the Kaluga region and for the Klimovskiy district of the Bryansk region [4]. For the Gordeevskiy, Klintsovskiy, and Krasnogorskiy districts, the date of introducing countermeasures is 10 May 1986 (the date for Novozybkovskiy district is 05 May 1986) [4]. It was found that individual thyroid dose distributions are very similar to the log normal type of statistical distribution [3– 5]. Tables 1 –8 provide the main experimental parameters of such kind of distributions for seven districts in Kaluga’s database, where a lot of measurements were performed: number of records, maximum individual dose (MID), mean arithmetical dose (DA) and standard deviation (SD), median dose (DM) and geometric standard deviation (GSD) for different age groups. Table 9 presents the mean and median thyroid doses for adult persons in five districts of the Bryansk region. All doses are presented in mGy. The obtained data were used for the validation of the semi-empirical model for thyroid dose reconstruction [4]. This allowed the reconstruction of the mean doses for Russian settlements in the contaminated territories of the Bryansk, Kaluga, Tula, and Orel regions, where I-131 measurements were not performed [5]. The dynamics of I-131 fallout and the dates of the beginning of the local pasture period were taken into account. The values of the collective thyroid doses for the Bryansk and Kaluga regions were estimated as 72 600 and 3400 persons-Gy (for population of 1137 100 and 213 500 inhabitants). The corresponding values for the Tula and Orel regions are 13 400 and 16 900 persons-Gy (for population of 1 310 100 and 448 000 inhabitants).

4. Discussion Re-evaluation of the thyroid doses for the Russian contaminated territories were based on the available data, including dynamics of I-131 fallout and of the beginning of the pasture period. Efforts are now underway to refine the performed dose estimates in a second run and to assess the appropriate dose uncertainties. The following activities are in progress now: development of a method of thyroid dose reconstruction based on measurements of the deposition density of I-129 (for the territories where I-131 measurements were not performed—see paper by Hoshi et al. in this issue); more correct dose estimation, including the wet or dry types of fallout (for the territories where this information is not available—see Ref. [7] concerning ‘‘birch tree effect’’ as an indicator of fallout type).

5. Conclusions Re-estimations of individual thyroid doses for Kaluga’s and Bryansk’s databases (27 615 total personal values) were based on recently published data concerning dynamics of fallout and the dates of the pasture period. According to new estimations, the median of individual dose values in the Kaluga database (seven raions) varies from 30 mGy for children to 8 mGy for adults (GSD about 2.6). In the database of Bryansk (five raions), the median dose values are ranging from 140 mGy for children to 30 mGy for adults (GSD about 2.7). The obtained

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data were used for the validation of the semi-empirical model for thyroid dose reconstruction. This allowed the reconstruction of the mean doses for the settlements, where I-131 measurements were not performed. The new estimations of collective doses differ from those which were published before [2,8]. The collective thyroid doses for the Bryansk and Kaluga regions were estimated as 72 600 and 3400 person-Gy (for population of 1137 100 and 213 500 inhabitants). The corresponding values for the Tula and Orel regions are 13 400 and 16 900 person-Gy (for population of 1 310 100 and 448 000 inhabitants).

Acknowledgements This work was supported by The Ministry of Public Health of the Russian Federation. The part of this work was supported by Hiroshima University, Japan.

References [1] A.F. Tsyb, E.M. Parshkov, V.V. Shakhtarin, V.F. Stepanenko, V.G. Skvortsov, I.V. Chebotareva, Thyroid cancer in children and adolescents of Bryansk and Kaluga regions, in: A. Karaoglou, G. Desmet, G.N. Kelly, H.G. Menzel (Eds.), The Radiological Consequences of the Chernobyl Accident, Proceedings of the First International Conference (Minsk, Belarus, 18 – 22 March 1996), European Commission and the Belarus, Russian and Ukrainian Ministries on Chernobyl Affairs, Emergency Situation and Health, Luxembourg, 1996, pp. 691 – 698, EUR 16544 EN. [2] L.A. Ilyin, M.I. Balonov, L.A. Buldakov, V.N. Buriak, K.I. Gordeev, S.I. Dementev, I.G. Zhsakov, G.A. Zubovsky, A.I. Kondrusev, Yu. Konstantinov, I.I. Linge, I.A. Likhtarev, A.M. Liaginskaya, V.A. Matyukhin, O.A. Pavlovsky, A.I. Potapov, A.E. Prisiazsnyuk, P.V. Ramsaev, A.E. Romanenko, M.N. Savkin, N.T. Starkova, N.D. Tronko, A.F. Tsyb, V.F. Stepanenko, V.K. Ivanov, Ecological peculiarities, medical and biological consequences of the Chernobyl accident, Med. Radiol. 34 (11) (1989) 59 – 81 (in Russian). [3] A.F. Tsyb, E.G. Matveenko, V.F. Stepanenko, V.A. Pitkevich, et al., Results of dosimetrical and medical investigation of the population in the Kaluga region after the Chernobyl accident. Report to the Ministry of Public Health. Part 1 and Part 2. Obninsk: MRRC RAMS, 1986 (in Russian). [4] V.T. Khrousch, Yu.I. Gavrilin, S.M. Shinkarev, A.B. Smirnov, A.B. Rusanova, O.E. Ivanova, V.F. Stepanenko, A.E. Kondrashov, E.K. Yaskova, D.V. Petin, K.P. Makhonko, M.Yu. Orlov, E.V. Spirin, N.N. Isamov, M.I. Balonov, I.A. Zvonova, A.A. Bratilova. Systematisation of thyroid doses in residents of Russian territories contaminated as a result of the Chernobyl accident. Report 6.5.1.6.2-96 to the Ministry of Public Health of Russia (with Supplements). Moscow: IBPh, 1996 (in Russian). [5] V.F. Stepanenko, A.F. Tsyb, E.M. Parshkov, V.V. Shakhtarin, A.E. Kondrashov, V.G. Skvortsov, E.K. Iaskova, A.I. Ivannikov, N.V. Belorukova, L.I. Moskovko, et al., Retrospective thyroid absorbed doses estimation in Russia following the Chernobyl accident: progress and application to dosimetrical evaluation of childhood thyroid cancer morbidity, in: M. Hoshi, J. Takada, R. Kim, Y. Nitta (Eds.), Effects of Low-level Radiation for Residents Near Semipalatinsk Nuclear Test Site, Proceedings of the Second Hiroshima International Symposium, Hiroshima University, Hiroshima, 1996, pp. 31 – 84. [6] K.P. Makhonko, E.G. Kozlova, A.A. Volokitin, Radioiodine accumulation on soil and reconstruction of doses from iodine exposure on the territory contaminated after the Chernobyl accident, Radiation and Risk, Bulletin of the National Radiation and Epidemiological Registry, English Translation of Russian issue N7, 1997, pp. 90 – 142, Cambridge, MA. [7] V.F. Stepanenko, Yu.I. Gavrilin, V.P. Snykov, V.E. Shevchuk, H.Y. Go¨ksu, P.G. Voilleque´, M.Yu. Orlov, Elevated exposure rates under inclined birch trees indicate the occurrence of rainfall during radioactive fallout from Chernobyl, Health Phys. 2001 (in press). [8] I.A. Zvonova, M.I. Balonov, Radioiodine dosimetry and prediction of consequences of thyroid exposure of Russian population following the Chernobyl accident, The Chernobyl Papers, 1993, pp. 71 – 126, Richland, WA.