The experience of individual dose reconstruction after uncontrolled large-scale irradiation of population

There are three main methods available to obtain retrospective assessments of radiation dose: a) computational modeling (CM), which use archive monitoring data of radioactive contamination of soils, biota and human body are applied to develop radioecological models for estimation of mean doses. Individualization of mean calculated doses is performed using results of individual questioning of the inhabitants of the contaminated territories. The evaluation of the uncertainty of doses is provided by Monte Carlo method with a variation of parameters of the models; b) the retrospective luminescence dosimetry (RLD) and c) ESR dosimetry, determine the cumulative absorbed dose in the bricks of buildings and in human tooth enamel, respectively. RLD and ESR dosimetry methods allow the estimation of accumulated dose with accuracy of 20-30 mGy Estimates of dose obtained by applying CM, RLD and ESR methods downwind the Chernobyl NPP and to Semipalatinsk nuclear test site (SNTS) are overviewed in the paper. The comparisons of dose estimates by different methods are pesented. Key technologies, methods and equipment, application areas, technology target, methods developed, categories of investigated subjects are the following: Key approaches and technologies. Radioecological models and individual dosimetrical questionnaires for individual dose estimations by modeling calculations (MC), Retrospective Luminescence Dosimetry (RLD) with quartz inclusions, Electron Spin Resonance (ESR) dosimetry with human tooth enamel; Methods and equipment. RISOE luminescence reader, Brucker ESR spectrometer, know-how spectra processing software, know-how sampling and sample preparation methodology. Application areas: -Individual retrospective dosimetry in support to radiation epidemiological studies; -Retrospective dosimetry in support to making decision regarding mitigation of the health consequences of large scale radiation accidents; -Retrospective dosimetry in a case of local radiation accidents with radioactive sources; -Retrospective instrumental estimation of radiation doses in a cases of uncontrolled (accidental) irradiation of personnel or patients in a course or radiation therapy. Target: to develop and to harmonize the system of methods of retrospective dosimetry for national and worldwide distribution. Methods developed: radioecological models and individual dosimetrical questionnaires for individual dose estimations by modeling calculations; retrospective luminescence dosimetry with quartz inclusions in the bricks of the buildings; retrospective ESR dosimetry with human tooth enamel. Categories of investigated subjects: Population of territories contaminated following the Chernobyl accident (Russian Federation) – Fig. 1.; Population of territories around Semipalatinsk nuclear test site (Russian Federation and Republic of Kazakhstan)Fig. 2. Fig.1. Example [1,2]. Map with indication of raions of Bryansk oblast (Russian Federation), which were contaminated resulting the Chernobyl accident. 221 km of distance from Chernobyl NPP to the most contaminated settlement Zaborie village (soil contamination density by 137 Cs 4300 kBq/m 2 ). Fig.2. Example [3]. The 1st A-bomb test in former USSR (29.08.1949) – the radioactive trace in Kazakhstan and Russia with indication of investigated settlements. NTS – Semipalatinsk nuclear test site. Monitoring of 131 I activity in thyroid gland and development of thyroid dose reconstruction approach among inhabitants of territories contaminated by radionuclides as a result of the Chernobyl accident (Russian Federation). During May of 1986 the massive monitoring of 131 I activity in thyroid gland among inhabitants of Russian territories contaminated by radionuclides as a result of Chernobyl accident was performed [4,5]. During 3 weeks on May of 1986 26 724 inhabitants of 115 contaminated settlements of 7 subregions (raions) were monitored in Kaluga region (RF) [6]. The detailed description of developed technology of dose monitoring and of methods of thyroid dose estimations are presented in [4,5,7]. Individual thyroid doses were estimated for each monitored person with accounting for real dose forming factors on May of 1986 year [6]. As to Kaluga region, the maximal thyroid doses were estimated in 3 contaminated subregions – Ul’ianovoskiy, Zhsizdrinskiy, Khvastovochskiy (see Table 1 as well for 7 investigated subregions in total [5]). It was found on the early stage of investigation (1986 year) that statistical distribution of individual thyroid doses is characterized by “long tail” in the individual dose range, which is much higher than mean and median doses for different age groups [4]. Table 1. Example [5]. Thyroid absorbed doses in different age groups of investigated inhabitants of 7 subregions of Kaluga region. *) N-number of investigated persons; MID-maximal individual dose; DA-average dose for given age group; DM-median dose for given age group; GSDgeometric standard deviation. The results of massive monitoring of thyroid doses among inhabitants of contaminated territories of Kaluga region were combined with the similar data related to contaminated territories of Bryansk region (Russia) and Republic of Belarus. As a result the individual thyroid dose reconstruction approach was developed for persons who were not monitored just after the accident (on May, 1986): it is radioecological semiempirical model and individual dosimetrical questionnaires for individual dose estimations by modeling calculations [4,5,7-10]. The developed approach of individual thyroid dose reconstruction is still actual for implementation in a cases of possible large scale radiations accidents. Figure 3 shows an example of comparison of individual thyroid doses: calculated individual thyroid doses VS dose estimations based on the results of 131 I measurements in thyroid gland among inhabitants of contaminated territories of Bryansk region are presented [7]. Fig. 3. An example [7] of comparison of individual thyroid doses: calculated individual doses (D 2, mGy) VS dose estimations based on the results of 131 I measurements in thyroid gland ( D 1, mGy) among inhabitants of contaminated territories of Bryansk region. Monitoring of 137 Cs activity in whole body and development of whole body internal dose reconstruction approach among inhabitants of territories contaminated by radionuclides as a result of the Chernobyl accident (Russian Federation). Starting from the fall of 1986 year till 2001 year the massive monitoring of 137 Cs activity in whole body among inhabitants of Russian territories contaminated by radionuclides as a result of Chernobyl accident was performed [11]. The detailed description of methodology developed and equipment used are presented in [12]. The results of massive monitoring of 137 Cs activity in whole body were applied for developing of approach Values*) Thyroid absorbed doses for different age groups, mGy. (age groups, years, are related to the moment of the accident) 1-2 >2-7 >7-12 >12-17 >17 N 1075 989 7491 6440 4997 5732 MID, mGy 550 530 460 320 250 250 DA, mGy 52 43 23 15 14 13 DM, mGy 31 26 14 10 8.3 8.1 GSD 2,7 2,7 2,6 2,4 2,7 2,7 of individual whole body dose reconstruction for persons who were not monitored: it is radioecological model and individual dosimetrical questionnaires for individual dose estimations by modeling calculations [13]. The developed approach of individual whole body internal dose reconstruction is still actual for implementation in a cases of possible large scale radiations accidents. As in a case of thyroid gland irradiation, it was found that statistical distribution of individual whole body doses of internal irradiation is characterized by “long tail” in the individual dose range, which is much higher than mean and median doses [12]. Figure 4 shows an example of statistical distribution of individual whole body doses of internal irradiation among inhabitants of contaminated territories of Bryansk region. Figure 4. Statistical distribution of individual whole body doses of internal irradiation (Bryansk region). On the horizontal axis ( Di , mSv): Results of estimation of individual whole body doses of internal irradiation on the base of 137 Cs activity measurements in whole body of inhabitants of contaminated territories of Bryansk region whole body doses accumulated during 15 years after the Chernobyl accident (total number of monitored persons 34 834); Results of estimation of individual whole body doses of internal irradiation on the base of developed approach of dose reconstruction (radioecological model and individual dosimetrical questionnaires) whole body doses accumulated during 15 years after the Chernobyl accident (total number of questioned persons – 1 456); On the vertical axis n,%: Percentage from total number of persons with available results of 137 Cs measurements (total number of these persons – 34 834) Percentage from total number of persons with available individual questionnaires (total number of these persons – 1 456) Figures 5 and 6 shows an examples of comparison of individual whole body doses of internal irradiation: calculated individual doses VS dose estimations based on the results of 137 Cs measurements in whole body among inhabitants of contaminated territories of Bryansk region are presented. Comparisons were performed for the same persons, which have data of 137 Cs measurements and data of individual questioning as well. Figure 5 – 1 st year after the accident (D2 = (1.24±0.25)×D1 + 1.7±2.1; R=0.98, р<0.01). Figure 6 – 15th year after the accident (D2= (1.02±0.15)×D1 + 0.12±0.41; R=0.94, р<0.01). 0 50 100 150 200 250 0 50 100 150 200 D1 D2