Interlaboratory comparison of tooth enamel dosimetry on Semipalatinsk region: Part 2, Effects of spectrum processing

Interlaboratory comparison of electron paramagnetic resonance tooth enamel dosimetry with investigations of the dose responses of the standard samples

A total of seven Japanese laboratories participated in an intercomparison study to estimate the dose given to tooth enamel samples, using the electron spin resonance method. Each of four of the participating laboratories prepared a set of tooth enamel samples, using the electron spin resonance method. Four of the participating laboratories each prepared a set of tooth enamel samples, consisting of seven standard aliquots irradiated from 100 to 2000 mGy and three samples with an 'unknown' dose between 140 and 960 mGy, were intended to eliminate bias from sample preparation. Although not all seven laboratories measured all four sets of samples, the major finding was that systematic biases in estimating doses may be caused by differences in laboratory measurements rather than by the enamel extracting procedures. When doses were averaged by measurements made by multiple laboratories, the averaged values were close to the actual values. Scattering in the intercepts in the standard dose response would be a serious problem in actual dosimetry where no background sample is available.

Electron paramagnetic resonance dose measurements in teeth of tissue donors to the United States Transuranium and Uranium Registries

The United States Transuranium and Uranium Registries (USTUR) is a research program that studies actinide biokinetics in occupationally exposed individuals with known intakes of these elements. Electron paramagnetic resonance (EPR) in tooth enamel was applied to reconstruct external doses of nine USTUR registrants. Only in two cases there is a reasonable agreement between the EPR-measured dose and the worksite external dose record. For two registrants, high EPR doses can be explained by possible cancer radiotherapy. For the remaining five cases, EPR doses significantly exceed official occupational doses with no plausible explanation for the observed discrepancy. More EPR dose measurements need to be done to explain this anomaly.

Self-Organization Effects of Thin ZnO Layers on the Surface of Porous Silicon by Formation of Energetically Stable Nanostructures

The formation of complex surface morphology of a multilayer structure, the processes of which are based on quantum phenomena, is a promising domain of the research. A hierarchy of pore of various sizes was determined in the initial sample of porous silicon by the atomic force microscopy. After film deposition by spray pyrolysis, ZnO nanoclusters regularly distributed over the sample surface were formed. Using the electron paramagnetic resonance (EPR) method it was determined that the localization of paramagnetic centers occurs more efficiently as a result of the ZnO deposition. An increase in the number of deposited layers, leads to a decrease in the paramagnetic center relaxation time, which is probably connected with the formation of ZnO nanocrystals with energetically stable properties. The nucleation and formation of nanocrystals is associated with the interaction of particles with an uncompensated charge. There is no single approach to determine the mechanism of this process. By the EPR method supplemented with the signal cyclic saturation, spectral manifestations from individual centers were effectively separated. Based on electron paramagnetic resonance and photoluminescence studies it was revealed that the main transitions between energy levels are due to oxygen vacancies and excitons.

Tooth enamel ESR dosimetry for Hiroshima 'black rain' zone residents

Electron spin resonance (ESR) dosimetry was applied to human tooth enamel in order to obtain individual absorbed doses for victims of the Hiroshima bomb who lived in the 'black rain' area. The so-called 'black rain' fell in the form of precipitation on the western part of Hiroshima city and the northwestern suburbs within a few hours after the explosion of the atomic bomb on 6 August 1945, and exposed the population in this area. Only three tooth samples were collected from this area. Since the teeth were located at positions 1, 2 and 4, only the lingual portion was used for the analysis. The results showed that the excess dose after subtracting natural radiation for one (position 4; hh1) was background, for the second (position 2; hh2) it was 133 mGy, and for the other (position 1; hh3) it was 243 mGy. Based on these results, we further investigated the radiation dose attributed to dental X-rays and head CT scan. Such dose of the hh3 radiographic examination was estimated to be 57-160 mGy, which implies an additional exposure around 135 mGy after subtraction. On the other hand, the dose data of hh1 after subtracting dental X-rays was negative. This may mean that such additional doses are an overestimation. In addition, the effect of sunlight should be considered, which is the same direction of overestimation. As a result, the residual dose of 140 mGy suggests the inclusion of radiation from the 'black rain.'

RENEB/EURADOS field exercise 2019: robust dose estimation under outdoor conditions based on the dicentric chromosome assay

PURPOSE

Biological and/or physical assays for retrospective dosimetry are valuable tools to recover the exposure situation and to aid medical decision making. To further validate and improve such biological and physical assays, in 2019, EURADOS Working Group 10 and RENEB performed a field exercise in Lund, Sweden, to simulate various real-life exposure scenarios.

MATERIALS AND METHODS

For the dicentric chromosome assay (DCA), blood tubes were located at anthropomorphic phantoms positioned in different geometries and were irradiated with a 1.36 TBq 192Ir-source. For each exposure condition, dose estimates were provided by at least one laboratory and for four conditions by 17 participating RENEB laboratories. Three radio-photoluminescence glass dosimeters were placed at each tube to assess reference doses.

RESULTS

The DCA results were homogeneous between participants and matched well with the reference doses (≥95% of estimates within ±0.5 Gy of the reference). For samples close to the source systematic underestimation could be corrected by accounting for exposure time. Heterogeneity within and between tubes was detected for reference doses as well as for DCA doses estimates.

CONCLUSIONS

The participants were able to successfully estimate the doses and to provide important information on the exposure scenarios under conditions closely resembling a real-life situation.

Eurados review of retrospective dosimetry techniques for internal exposures to ionising radiation and their applications

This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal exposures are characterized by a spatially inhomogeneous irradiation of the body, which is potentially prolonged over large periods and variable over time, is particularly problematic for biological and electron paramagnetic resonance (EPR) dosimetry methods when compared with external exposures. The paper gives initially specific information about internal dosimetry methods, the most common cytogenetic techniques used in biological dosimetry and EPR dosimetry applied to tooth enamel. Based on real-case scenarios, dose estimates obtained from bioassay data as well as with biological and/or EPR dosimetry are compared and critically discussed. In most of the scenarios presented, concomitant external exposures were responsible for the greater portion of the received dose. As no assay is available which can discriminate between radiation of different types and different LETs on the basis of the type of damage induced, it is not possible to infer from these studies specific conclusions valid for incorporated radionuclides alone. The biological dosimetry assays and EPR techniques proved to be most applicable in cases when the radionuclides are almost homogeneously distributed in the body. No compelling evidence was obtained in other cases of extremely inhomogeneous distribution. Retrospective dosimetry needs to be optimized and further developed in order to be able to deal with real exposure cases, where a mixture of both external and internal exposures will be encountered most of the times.

APPLICATION OF EPR TOOTH DOSIMETRY FOR VALIDATION OF THE CALCULATED EXTERNAL DOSES: EXPERIENCE IN DOSIMETRY FOR THE TECHA RIVER COHORT

This study applies EPR tooth dosimetry for validation of external doses calculated with the TRDS-2016. EPR-based external dose in tooth enamel is calculated by subtraction of the contributions of natural and anthropogenic sources from the exposure of interest. These subtracted terms may contribute substantially to the overall uncertainty of the EPR-derived external dose. The validation method strongly depends on the uncertainties. The current study combines the results of a number of previous papers to propagate the uncertainty of EPR-derived external doses. It is concluded that the overall uncertainties of D ≥ 500 mGy are comparable with measurement uncertainties (≤30%); the overall uncertainties of D < 500 mGy become higher as the EPR-dose decreases because they are strongly effected by all other factors of influence. More than 70% of investigated individuals were exposed externally to doses <100 mGy with uncertainties >100%. Therefore, the validation task can be solved only based on statistical approaches. The validation of the TRDS-2016 predictions demonstrates good convergence of group-averages with EPR-based doses. The method for validation of the uncertainty of TRDS-2016 predictions should be also designed based on statistical approaches.

EPR DOSIMETRY STUDY FOR POPULATION RESIDING IN THE VICINITY OF FALLOUT TRACE FOR NUCLEAR TEST ON 7 AUGUST 1962

The method of electron paramagnetic resonance (EPR) dosimetry using extracted teeth has been applied to human tooth enamel to obtain individual absorbed doses of residents of settlements in the vicinity of the central axis of radioactive fallout trace from the contaminating surface nuclear test on 7 August 1962. Most of the settlements (Kurchatov, Akzhar, Begen, Buras, Grachi, Mayskoe, Semenovka) are located from 70 to 120 km to the North-East from the epicenter of the explosion at the Semipalatinsk Nuclear Test Site (SNTS). This region is basically an agricultural region. A total of 57 teeth samples were collected from these sites. Eight teeth from residents of the Kokpekty settlement, which was not subjected to any radioactive contamination and located 400 km to the Southeast from SNTS, were chosen as a control. The principal findings, using this method, were that the average excess dose obtained after subtraction of the natural background radiation was 13 mGy and ranged up to about 100 mGy all for residents in this region.

External dose reconstruction in tooth enamel of Techa riverside residents

This study summarizes the 20-year efforts for dose reconstruction in tooth enamel of the Techa riverside residents exposed to ionizing radiation as a result of radionuclide releases into the river in 1949-1956. It represents the first combined analysis of all the data available on EPR dosimetry with teeth of permanent residents of the Techa riverside territory. Results of electron paramagnetic resonance (EPR) measurements of 302 teeth donated by 173 individuals living permanently in Techa riverside settlements over the period of 1950-1952 were analyzed. These people were residents of villages located at the free-flowing river stream or at the banks of stagnant reservoirs such as ponds or blind river forks. Cumulative absorbed doses measured using EPR are from several sources of exposure, viz., background radiation, internal exposure due to bone-seeking radionuclides (⁸⁹Sr, ⁹⁰Sr/⁹⁰Y), internal exposure due to ¹³⁷Cs/^137mBa incorporated in soft tissues, and anthropogenic external exposure. The purpose of the present study was to evaluate the contribution of different sources of enamel exposure and to deduce external doses to be used for validation of the Techa River Dosimetry System (TRDS). Since various EPR methods were used, harmonization of these methods was critical. Overall, the mean cumulative background dose was found to be 63 ± 47 mGy; cumulative internal doses due to ⁸⁹Sr and ⁹⁰Sr/⁹⁰Y were within the range of 10-110 mGy; cumulative internal doses due to ¹³⁷Cs/^137mBa depend on the distance from the site of releases and varied from 1 mGy up to 90 mGy; mean external doses were maximum for settlements located at the banks of stagnant reservoirs (~500 mGy); in contrast, external doses for settlements located along the free-flowing river stream did not exceed 160 mGy and decreased downstream with increasing distance from the site of release. External enamel doses calculated using the TRDS code and derived from the EPR measurements were found to be in good agreement.

EPR pilot study on the population of Stepnogorsk city living in the vicinity of a uranium processing plant

The aim of this pilot study was to evaluate possible doses in teeth received by workers of a uranium processing plant, in excess to the natural background dose. For this, the electron paramagnetic resonance dosimetry method was applied. Absorbed doses in teeth from the workers were compared with those measured in teeth from the Stepnogorsk city population and a control pool population from Astana city. The measured tooth samples were extracted according to medical indications. In total, 32 tooth enamel samples were analyzed, 5 from Astana city, Kazakhstan (control population), 21 from the residents of Stepnogorsk city (180 km from Astana city), and 6 from the workers of a uranium processing plant. The estimated doses in tooth enamel from the uranium processing plant workers were not significantly different to those measured in enamel from the control population. In teeth from the workers, the maximum dose in excess to background dose was 33 mGy. In two teeth from residents of Stepnogorsk city, however, somewhat larger doses were measured. The results of this pilot study encourage further investigations in an effort to receiving a final conclusion on the exposure situation of the uranium processing plant workers and the residents of Stepnogorsk city.

Q-band electron paramagnetic resonance dosimetry in tooth enamel: biopsy procedure and determination of dose detection limit

High-frequency Q-band (37 GHz) electron paramagnetic resonance (EPR) dosimetry allows to perform fast (i.e., measurement time <15 min) dose measurements using samples obtained from tooth enamel mini-biopsy procedures. We developed and tested a new procedure for taking tooth enamel biopsy for such dose measurements. Recent experience with EPR dose measurements in Q-band using mini-probes of tooth enamel has demonstrated that a small amount of tooth enamel (2-10 mg) can be quickly obtained from victims of a radiation accident. Accurate dose assessments can further be carried out in a very short time to provide important information for medical treatment. Here, the Q-band EPR dose detection limit for 5 and 10 mg samples is estimated to be 367 and 248 mGy, respectively. These values are comparable to the critical parameters determined for conventional X-band EPR in tooth enamel.

Review of reconstruction of radiation incident air kerma by measurement of absorbed dose in tooth enamel with EPR

Electron paramagnetic resonance dosimetry with tooth enamel has been proved to be a reliable method to determine retrospectively exposures from photon fields with minimal detectable doses of 100 mGy or lower, which is lower than achievable with cytogenetic dose reconstruction methods. For risk assessment or validating dosimetry systems for specific radiation incidents, the relevant dose from the incident has to be calculated from the total absorbed dose in enamel by subtracting additional dose contributions from the radionuclide content in teeth, natural external background radiation and medical exposures. For calculating organ doses or evaluating dosimetry systems the absorbed dose in enamel from a radiation incident has to be converted to air kerma using dose conversion factors depending on the photon energy spectrum and geometry of the exposure scenario. This paper outlines the approach to assess individual dose contributions to absorbed dose in enamel and calculate individual air kerma of a radiation incident from the absorbed dose in tooth enamel.

Review of retrospective dosimetry techniques for external ionising radiation exposures

The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements.

Estimation of background radiation doses for the Peninsular Malaysia's population by ESR dosimetry of tooth enamel

Background radiation dose is used in dosimetry for estimating occupational doses of radiation workers or determining radiation dose of an individual following accidental exposure. In the present study, the absorbed dose and the background radiation level are determined using the electron spin resonance (ESR) method on tooth samples. The effect of using different tooth surfaces and teeth exposed with single medical X-rays on the absorbed dose are also evaluated. A total of 48 molars of position 6-8 were collected from 13 district hospitals in Peninsular Malaysia. Thirty-six teeth had not been exposed to any excessive radiation, and 12 teeth had been directly exposed to a single X-ray dose during medical treatment prior to extraction. There was no significant effect of tooth surfaces and exposure with single X-rays on the measured absorbed dose of an individual. The mean measured absorbed dose of the population is 34 ± 6.2 mGy, with an average tooth enamel age of 39 years. From the slope of a regression line, the estimated annual background dose for Peninsular Malaysia is 0.6 ± 0.3 mGy y(-1). This value is slightly lower than the yearly background dose for Malaysia, and the radiation background dose is established by ESR tooth measurements on samples from India and Russia.

EPR dosimetry with tooth enamel: A review

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.

Dental enamel EPR dosimetry: comparative testing of the spectra processing methods for determination of radiation-induced signal amplitude

The aim of this investigation is to find out the optimal algorithm for mathematical processing of the EPR spectra of irradiated tooth enamel for estimating the amplitude of the radiation-induced signal, which is used for determination of the absorbed dose in enamel for retrospective individual dosimetry. A recently developed analytical model, which takes into account the line shape variation of the enamel EPR spectral components registered at different microwave power, was applied to spectra processing in various operation modes to simulate spectra processing techniques differing by the number of fitted parameters. The precision of dose determination at spectra processing was assessed by the root mean square deviation between experimental and nominal doses for sets of spectra of enamel samples irradiated in different doses and measured at different microwave power. It is shown that in the case of pooled enamel samples prepared as a mixture from different teeth, the higher precision of spectra processing is obtained using a model with fixed native background signal line shape (characterized by width and asymmetry parameters). In case of individual samples prepared each from a different tooth, better results are obtained using a model with variable background signal line shape.

ESR dosimetry study on population of settlements nearby Ust-Kamenogorsk city, Kazakhstan

The method of electron spin resonance (ESR) dosimetry has been applied to human tooth enamel, to obtain individual absorbed doses of residents of settlements in vicinity of Ust-Kamenogorsk city, Kazakhstan (located about 400 km to the east from the epicenter of explosion at the Semipalatinsk Nuclear Test Site, SNTS). This region developed as a major mining and metallurgical center during the Soviet period (uranium production). Most of the investigated settlements (Ust-Kamenogorsk city, Glubokoe, Tavriya, Gagarino) are located near the central axis of the radioactive fallout trace that originated from the surface nuclear test on 24 August 1956, while the Kokpekty settlement (located 400 km to the Southeast from SNTS) was chosen as a control because it was not subjected to any radioactive contamination. In total, 44 samples were measured. It was found that the excess doses obtained after subtraction of natural background radiation ranged up to about 114 mGy for residents of Ust-Kamenogorsk city, whose tooth enamel was formed before 1956. For residents of Gagarino, excess doses did not exceed 47 mGy for all ages. For residents of Tavriya, the maximum excess dose was 54 mGy, while for residents of Glubokoe it was about 58 mGy. For the population of the Shemonaikha settlements located at a distance of about 70 km from the central axis of the radioactive fallout trace, highest excess doses were 110 mGy. These high doses may be due to the influence of uranium enterprises located in that region, but probably not due to dental X-ray irradiation. For a final conclusion on the radiological situation in this region, the number of samples was too small and, therefore, more work is required to obtain representative results.

Measurement of absorbed doses from X-ray baggage examinations to tooth enamel by means of ESR and glass dosimetry

The contribution of radiation from X-ray baggage scans at airports on dose formation in tooth samples was investigated by electron spin resonance (ESR) dosimetry and by glass dosimetry. This was considered important, because tooth samples from population around the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan, had been transported in the past to Hiroshima University for retrospective dose assessment of these residents. Enamel samples and glass dosimeters were therefore examined at check-in time at Kansai airport (Osaka, Japan), Dubai airport (Dubai, United Arab Emirates) and Domodedovo airport (Moscow, Russia). These airports are on the route from Kazakhstan to Japan. Three different potential locations of the samples were investigated: in pocket (without X-ray scans), in a small bag (with four X-ray scans) and in large luggage (with two X-ray scans). The doses obtained by glass and ESR dosimetry methods were cross-compared. As expected, doses from X-ray examinations measured by glass dosimetry were in the microGy range, well below the ESR detection limit and also below the doses measured in enamel samples from residents of the SNTS.

Investigation of some parameters influencing the sensitivity of human tooth enamel to gamma radiation using electron paramagnetic resonance

Electron paramagnetic resonance (EPR) has been successfully used as a physical technique for gamma radiation dose reconstruction using calcified tissues. To minimize potential discrepancies between EPR readings in future studies, the effects of cavity response factor, tooth position and donor gender on the estimated gamma radiation dose were studied. It was found that the EPR response per sample mass used for assessment of doses in teeth outside of the 70-100 mg range should be corrected by a factor which is a function of the sample mass. In the EPR measurements, the difference in sensitivity of different tooth positions to gamma-radiation was taken into consideration. It was determined that among all the pre-molars and molars tooth positions, the relative standard deviation of sensitivity was 6.5%, with the wisdom teeth and the first molars having the highest and lowest sensitivity to gamma-radiation, respectively. The current results reveal no effect of the donor gender on the sensitivity to gamma-radiation.