Considerations Regarding the Implementation of EPR Dosimetry for the Population in the Vicinity of Semipalatinsk Nuclear Test Site Based on Experience from Other Radiation Accidents

Valeriy SKVORTSOV Alexander IVANNIKOV Dimitri TIKUNOV Valeriy STEPANENKO Natalie BORYSHEVA Sergey ORLENKO Mikhail NALAPKO Masaharu HOSHI EPR (ESR) spectroscopy/Tooth enamel/Radiation dose/Chernobyl/Semipalatinsk nuclear test site. General aspects of applying the method of retrospective dose estimation by electron paramagnetic resonance spectroscopy of human tooth enamel (EPR dosimetry) to the population residing in the vicinity of the Semipalatinsk nuclear test site are analyzed and summarized. The analysis is based on the results obtained during 20 years of investigations conducted in the Medical Radiological Research Center regarding the development and practical application of this method for wide-scale dosimetrical investigation of populations exposed to radiation after the Chernobyl accident and other radiation accidents. - Retrospective dose estimation for the population residing in the vicinity of the Semipalatinsk nuclear test site (SNTS) remains an urgent question, because of the need to estimate the risks of radiation effects in the population in order to forecast medical consequences of the radiation exposure. Information about the nuclear tests conducted in SNTS, the radioactive contamination of the adjacent territories, the medical effects, and the results of dose reconstruction have been presented elsewhere.111) Dose reconstruction methods based on radioloecological modeling provide geographical averages or conservative estimates of the doses.11) The retrospective luminescence dosimetry (RLD) method using quartz inclusions in building materials gives estimates of local doses, which are related to the locations of sampling of quartz containing materials.10,12,13,14) However in radioepidemiological studies analysis of dose-effect relationships should be based whenever possible on individual dose estimates, i.e., estimates that take into account the actual exposure circumstances of each study subject.15) There are two physical methods relevant to retrospective estimation of individual doses. The first method, sometimes called dose reconstruction, is based on radioecological modeling with further individualization of dose estimates using data about individual dose-determining factors, such as quantities and sources of food and milk consumed, behavioral factors, conditions of living, relocations, etc.16) This method has typically been used for dose estimation in radioepidemiological case-control and cohort studies, since such studies require the application of a uniform dosimetry method for all investigated cases and controls. The second method is electron paramagnetic resonance (EPR) spectroscopy of human tooth enamel (EPR dosimetry).17) Application of EPR tooth enamel dosimetry is limited to subjects with available teeth samples, which can be extracted only for valid medical indications. Nevertheless this instrumental method is very useful for validation of individual doses estimated by dose reconstruction, when such dose estimates can be compared to EPR dose estimates for the same persons.18,19) To date only a few publications have addressed individual dose estimation by EPR dosimetry for the population of the vicinity of SNTS.19,20,21,22) Further investigation by EPR dosimetry should be continued and expanded in this region. The experience obtained in wide scale application of this method in other regions should be taken into account.23,24,25) The objective of this paper is to summarize the lessons learned from wide-scale application of EPR dosimetry by the Medical Radiological Research Center (MRRC), Russia, in the Chernobyl-affected area and at other radiation accidents and to identify important aspects of using this method at dose reconstruction in the vicinity of SNTS. MAIN FINDINGS AND DISCUSSION Principal findings obtained from the application of the EPR dosimetry in exposed populations Work in the field of EPR dosimetry began about 20 years ago at the MRRC.23) Since then, large-scale investigations by this method have been performed to support estimation of radiation effects following various radiation accidents. In studies of the consequences of Chernobyl, EPR dosimetry was used for dosimetric evaluation of the population of territories contaminated by radioactive fallout from the Chernobyl accident (about 3000 samples from Bryansk region, Russia) and for populations of uncontaminated (control) territories (about 500 samples, Russia), and for dose estimation among radiation emergency workers in Chernobyl NPP (about 120 samples).18,19,24,25) Examples of distributions of estimated doses caused by radiation from the Chernobyl accident, i.e., additional to background doses, are presented in Fig. 1 for several of the investigated groups. EPR dosimetry has also been applied to personnel of former USSR Navy submarines who were irradiated in nuclear reactor accidents25,26) and to the population of the radioactively contaminated region of the Techa River in South Ural, Russia.27) Some joint investigations of dose estimation using teeth samples collected in the vicinity of SNTS were performed by MRRC and Hiroshima University.20) Dosimetrical investigation of a population by EPR dosimetry involves the following stages: sample collection, sample preparation, spectra measurement, spectra processing, EPR signal dose response calibration, dose and dose uncertainty estimation, and interpretation of the results. The main findings obtained by MRRC for improving each of these steps are presented below. Sample collection About 3500 teeth samples from residents of the Chernobyl-affected area and control (radiation-free) territories were collected and investigated by MRRC. Based on this experience,18,19) we proposed that the following information be collected for every sample. This includes information about the subject; (subjects full name or other unique identifier, address of permanent residence, birth date, gender, residences and relocations during the period since the radioactive contamination of the territory); about the tooth (type of tooth according to its position); about other exposures to ionizing radiation (occupational exposure including time of military service; X-ray medical procedures in the area of teeth, etc., including dates or periods of exposure and doses if possible); and about the collection of the tooth (institution and Fig. 1. Examples of statistical distributions of accidental (additional to background) doses (Dadd): for population of control (not contaminated) territories in Russia (a), for territories of Russia, which were contaminated following the Chernobyl accident - Gordeevsky district of Bryansk region (b), Uzlovski district of Tula region (c), for Chernobyl emergency workers (liquidators) (d). person responsible for collection, date of extraction). Also, it is desirable to have additional information about samples, such as description of the extracted tooth (permanent or deciduous, carious cavities, non-carious damage of the (...truncated)