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PubMed2006

Report from the techa river dosimetry review workshop held on 8-10 December 2003 at The State Research Centre Institute of Biophysics, Moscow, Russia.

Large releases of fission products into the Techa River, in the Southern Urals, occurred in 1950 and 1951, during the early years of operation of the Mayak Production Association (Mayak PA), which produced plutonium for nuclear weapons. Increases of leukemia and of solid cancers with radiation dose have been noted in the population of about 30,000 people who lived in the settlements downstream of the site of the radioactive releases; that population has been studied for several decades by Russian scientists, notably in the framework of cooperation with American and European scientists. The radiation doses are currently estimated by means of the Techa River Dosimetry System-2000 (TRDS-2000). Recently, a scientist from Mayak PA has suggested in several publications that the doses calculated using TRDS-2000 might be underestimated substantially. A special international Workshop, held in Moscow on 8-10 December 2003, aimed to resolve some of the pressing issues related to the determination of the external and internal doses received by the Techa River population and to give recommendations on the further development of methodologies used for dose reconstruction. The authors of this article were selected by the organizers of the Workshop to draw the conclusions of the meeting. They express the view that, while the dose reconstruction system TRDS-2000 is basically sound, additional work is needed and the results of any epidemiological studies making use of TRDS-2000 should be qualified as preliminary, pending resolution of several issues. The most important of these issues is the re-evaluation of the activities released, using additional information that could be obtained with the help of Mayak experts. Other specific suggestions aiming to improve the dose reconstruction methodology for the Techa River cohort, i.e., continued measurements of accumulated dose in environmental samples and human tissues, validation of external dose estimates with thermoluminescence measurements of bricks and with electron paramagnetic resonance measurements of teeth, estimation of individual doses instead of group doses, detailed account of the contributions to dose of medical examinations and of other releases from the Mayak complex, and careful assessment of the uncertainties, were made by the meeting participants.

Dose-Response Relationship, Radiation↗

PubMed2003

Quantification of low dose signal in EPR tooth dosimetry--a novel approach.

For radiation exposures below 100 mGy, the dosimetric signal in tooth enamel is too small to be measured by using the traditional dose reconstruction procedure. This is because low amplitude zero-added-dose signal can not be identified in an EPR spectrometer. A technique is presented wherein, zero-added-dose signal. when amplified by a proper known dose, can be measured in the EPR spectrometer. Mathematically, the accidental dose x is modified by a known amount of exposure, y (large enough so that the signal is now visible), and total exposure becomes x' = x + y, which is the modified-zero-added dose. The exposure x' is then quantified using the conventional backward extrapolation method and the accidental dose can be measured. In a laboratory controlled experiment, the feasibility of dose reconstruction in the 100 mGy range has been demonstrated. This may enable measurements of dose even due to suspected low exposure in tooth enamel.

Dental Enamel↗

PubMed2004

Spectrum reconstruction from dose measurements as a linear inverse problem.

There are three ways to determine the spectrum of a clinical photon beam: direct measurement, modelling the source and reconstruction from ion-chamber measurements. We focus on reconstruction because the necessary equipment is readily available and it provides independent confirmation of source models for a given machine. Reconstruction methods involve measuring the dose in an ion chamber after the beam passes through an attenuator. We gain information about the spectrum from measurements using attenuators of differing compositions and thicknesses since materials have energy dependent attenuation. Unlike the procedures used in other papers, we do not discretize or parametrize the spectrum. With either of these two approximations, reconstruction is a least squares problem. The forward problem of going from a spectrum to a series of dose measurements is a linear operator, with the composition and thickness of the attenuators as parameters. Hence the singular value decomposition (SVD) characterizes this operator. The right singular vectors form a basis for the spectrum, and, at first approximation, only those corresponding to singular values above a threshold are measurable. A more rigorous error analysis shows with what confidence different components of the spectrum can be measured. We illustrate this theory with simulations and an example utilizing six sets of dose measurements with water and lead as attenuators.

Computer Simulation↗

PubMed2005

Model testing using data on 131I released from Hanford.

The Hanford test scenario described an accidental release of 131I to the environment from the Hanford Purex Chemical Separations Plant in September 1963. Based on monitoring data collected after the release, this scenario was used by the Dose Reconstruction Working Group of BIOMASS to test models typically used in dose reconstructions. The primary exposure pathway in terms of contribution to human doses was ingestion of contaminated milk and vegetables. Predicted mean doses to the thyroid of reference individuals from ingestion of 131I ranged from 0.0001 to 0.8 mSv. For one location, predicted doses to the thyroids of two children with high milk consumption ranged from 0.006 to 2 mSv. The predicted deposition at any given location varied among participants by a factor of 5-80. The exercise provided an opportunity for comparison of assessment methods and conceptual approaches, testing model predictions against measurements, and identifying the most important contributors to uncertainty in the assessment result. Key factors affecting predictions included the approach to handling incomplete data, interpretation of input information, selection of parameter values, adjustment of models for site-specific conditions, and treatment of uncertainties.

Iodine Radioisotopes↗

PubMed1996

Uncertainty of historical measurements of 131I in Hanford-area vegetation.

The Hanford Environmental Dose Reconstruction (HEDR) Project was conducted to estimate the radiation dose that individuals could have received as a result of emissions to the air and water from Hanford Site operations since 1944. The largest doses were to the human thyroid gland from 131I released into the atmosphere from Hanford facilities in the 1945-1947 time period. In support of the dose reconstruction effort, a database of historical environmental radioactivity measurements was constructed. This database includes measurements of total radioactivity for vegetation samples collected from 1945-1948 and counted using a Geiger-Mueller (GM) detector system. Because the factors used at that time to convert the GM counts to 131I activity did not take all parameters into account, and because some parameter values were inaccurate, more accurate conversion factors were developed as part of the HEDR Project. These factors can be used to estimate the actual historical activity levels. This paper summarizes the Monte Carlo uncertainty and sensitivity analysis methods used to assess the uncertainty of the newly reconstructed historical vegetation 131I activities and to identify the parameters that contributed the most uncertainty to these reconstructed activities. Based on the study of two vegetation (sagebrush) samples collected in the mid-1940's, it appears that the true 131I activity of the historical vegetation samples should be within a factor of three of the reconstructed activity. Also, the uncertainty in the parameter Icf (the fraction of the background-corrected GM measurement of a vegetation sample that resulted from 131I) was found to contribute the most uncertainty to the reconstructed 131I activities when the uncertainty in Icf was large.

Air Pollutants, Radioactive↗

PubMedDate not supplied

Biophysical dose measurement using electron paramagnetic resonance in rodent teeth.

Electron paramagnetic resonance (EPR) dosimetry of human tooth enamel has been widely used in measuring radiation doses in various scenarios. However, there are situations that do not involve a human victim (e.g. tests for suspected environmental overexposures, measurements of doses to experimental animals in radiation biology research, or chronology of archaeological deposits). For such cases we have developed an EPR dosimetry technique making use of enamel of teeth extracted from mice. Tooth enamel from both previously irradiated and unirradiated mice was extracted and cleaned by processing in supersaturated KOH aqueous solution. Teeth from mice with no previous irradiation history exhibited a linear EPR response to the dose in the range from 0.8 to 5.5 Gy. The EPR dose reconstruction for a preliminarily irradiated batch resulted in the radiation dose of (1.4+/-0.2) Gy, which was in a good agreement with the estimated exposure of the teeth. The sensitivity of the EPR response of mouse enamel to gamma radiation was found to be half of that of human tooth enamel. The dosimetric EPR signal of mouse enamel is stable up at least to 42 days after exposure to radiation. Dose reconstruction was only possible with the enamel extracted from molars and premolars and could not be performed with incisors. Electron micrographs showed structural variations in the incisor enamel, possibly explaining the large interfering signal in the non-molar teeth.

Animals↗

PubMed2000

Preliminary report on the development of a virtually nondestructive additive dose technique for EPR dosimetry.

We propose a new approach to the additive dose method in EPR dosimetry studies for tooth enamel specimens. We outline a specialized routine whereby the sample may be left for the most part unirradiated, while only a small aliquot of the sample will be additively irradiated to relatively large doses. The routine is done in such a way so as not to significantly compromise either precision or accuracy of the dose reconstruction. It is also demonstrated that the overall throughput of the dose reconstruction is not appreciably compromised. With this potential ability, the utility of an international dose/sensitivity standard for EPR dosimetry of teeth is considered.

Dental Enamel↗

PubMed2003

Human health risk and exposure assessment of chromium (VI) in tap water.

Hexavalent chromium [Cr(VI)] has been detected in groundwater across the United States due to industrial and military operations, including plating, painting, cooling-tower water, and chromate production. Because inhalation of Cr(VI) can cause lung cancer in some persons exposed to a sufficient airborne concentration, questions have been raised about the possible hazards associated with exposure to Cr(VI) in tap water via ingestion, inhalation, and dermal contact. Although ingested Cr(VI) is generally known to be converted to Cr(III) in the stomach following ingestion, prior to the mid-1980s a quantitative analysis of the reduction capacity of the human stomach had not been conducted. Thus, risk assessments of the human health hazard posed by contaminated drinking water contained some degree of uncertainty. This article presents the results of nine studies, including seven dose reconstruction or simulation studies involving human volunteers, that quantitatively characterize the absorbed dose of Cr(VI) following contact with tap water via all routes of exposure. The methodology used here illustrates an approach that permits one to understand, within a very narrow range, the possible intake of Cr(VI) and the associated health risks for situations where little is known about historical concentrations of Cr(VI). Using red blood cell uptake and sequestration of chromium as an in vivo metric of Cr(VI) absorption, the primary conclusions of these studies were that: (1) oral exposure to concentrations of Cr(VI) in water up to 10 mg/L (ppm) does not overwhelm the reductive capacity of the stomach and blood, (2) the inhaled dose of Cr(VI) associated with showering at concentrations up to 10 mg/L is so small as to pose a de minimis cancer hazard, and (3) dermal exposures to Cr(VI) in water at concentrations as high as 22 mg/L do not overwhelm the reductive capacity of the skin or blood. Because Cr(VI) in water appears yellow at approximately 1-2 mg/L, the studies represent conditions beyond the worst-case scenario for voluntary human exposure. Based on a physiologically based pharmacokinetic model for chromium derived from published studies, coupled with the dose reconstruction studies presented in this article, the available information clearly indicates that (1) Cr(VI) ingested in tap water at concentrations below 2 mg/L is rapidly reduced to Cr(III), and (2) even trace amounts of Cr(VI) are not systemically circulated. This assessment indicates that exposure to Cr(VI) in tap water via all plausible routes of exposure, at concentrations well in excess of the current U.S. Environmental Protection Agency (EPA) maximum contaminant level of 100 microg/L (ppb), and perhaps those as high as several parts per million, should not pose an acute or chronic health hazard to humans. These conclusions are consistent with those recently reached by a panel of experts convened by the State of California.

Air Pollution, Indoor↗

PubMed2001

External doses to 350 m zone residents due to anisotropic radiation from the JCO criticality accident in Tokai-mura.

The validity of a method for individual dose reconstruction based on the anisotropic radiation distribution was confirmed by a comparison with the dose from Na-24 whole-body counting for seven persons at a neighboring company located on the western side of the JCO campus. The successful coincidence between Di (Na-24) and Di (present) also supports the validity of the second version of D(r) reported by the Head Office of Countermeasure. The present dose reconstruction for the 350 m zone at the western side showed an average value of 0.7 mSv and a maximal value of 3.1 mSv, as indoor-dose under the assumption of an effective transmittance of 0.4 for all of the houses. If all of the residents in 350 m zone were indoors during the accident, 83% of them might have received external doses of less than 1 mSv. The radiation exposure to the nearest residential area in the southern-west direction was significantly reduced with phi(theta(i)) between 0.4 and 0.2 by several buildings on the JCO campus. The present study on the public dose confirms that the official report on the public dose (the maximal value of 21 mSv for individual doses) from Head Office of Countermeasure is significantly overestimated due to their isotropic treatment of radiation from the source.

Anisotropy↗

PubMed2004

Effect of americium-241 alpha-particles on the dose-response of chromosome aberrations in human lymphocytes analysed by fluorescence in situ hybridization.

PURPOSE: To evaluate by the fluorescent in-situ hybridization (FISH) technique the dose-response and intercellular distribution of alpha-particle-induced chromosome aberrations. In particular, the validity of using the yield of characteristic types of chromosome abnormalities in stable cells as quantitative indicators for retrospective dose reconstruction has been evaluated. MATERIAL AND METHODS: Monolayers of human peripheral lymphocytes were exposed at doses from 0.02 to 1 Gy to alpha-particles emitted from a source of americium-241. The most probable energy of the alpha-particles entering the cells was 2.7 MeV. FISH painting was performed using DNA probes for chromosomes 2, 4 and 8 in combination with a pan-centromeric probe. In complete first-division cells, identified by harlequin staining, aberrations involving painted target chromosomal material were recorded as well as aberrations involving only unpainted chromosomal material. RESULTS: In total, the percentage of complex aberrations was about 35% and no dose dependence was observed. When complex-type exchanges were reduced to simple base types, the different cell distributions were clearly over-dispersed, and the linear coefficients of the dose-effect curves for translocations were significantly higher than for dicentrics. For past dose reconstruction, only a few complex aberrations were in stable cells. The linear coefficient obtained for transmissible aberrations in stable cells was more than seven times lower than that obtained in all analysed cells, i.e. including unstable cells. CONCLUSION: FISH-based analysis of complex rearrangements allows discrimination between partial-body exposures to low-linear energy transfer radiation and high-linear energy transfer exposures. In assessing past or chronic exposure to alpha-particles, the use of a dose-effect curve obtained by FISH-based translocation data, which had not excluded data determined in unstable cells, would underestimate the dose. Insertions are ineffective biomarkers because their frequency is too low.

Adult↗

PubMed2006

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis.

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

Electron Spin Resonance Spectroscopy↗

PubMed1998

Calibration of a portal imaging device for high-precision dosimetry: a Monte Carlo study.

Today electronic portal imaging devices (EPID's) are used primarily to verify patient positioning. They have, however, also the potential as 2D-dosimeters and could be used as such for transit dosimetry or dose reconstruction. It has been proven that such devices, especially liquid filled ionization chambers, have a stable dose response relationship which can be described in terms of the physical properties of the EPID and the pulsed linac radiation. For absolute dosimetry however, an accurate method of calibration to an absolute dose is needed. In this work, we concentrate on calibration against dose in a homogeneous water phantom. Using a Monte Carlo model of the detector we calculated dose spread kernels in units of absolute dose per incident energy fluence and compared them to calculated dose spread kernels in water at different depths. The energy of the incident pencil beams varied between 0.5 and 18 MeV. At the depth of dose maximum in water for a 6 MV beam (1.5 cm) and for a 18 MV beam (3.0 cm) we observed large absolute differences between water and detector dose above an incident energy of 4 MeV but only small relative differences in the most frequent energy range of the beam energy spectra. It is shown that for a 6 MV beam the absolute reference dose measured at 1.5 cm water depth differs from the absolute detector dose by 3.8%. At depth 1.2 cm in water, however, the relative dose differences are almost constant between 2 and 6 MeV. The effects of changes in the energy spectrum of the beam on the dose responses in water and in the detector are also investigated. We show that differences larger than 2% can occur for different beam qualities of the incident photon beam behind water slabs of different thicknesses. It is therefore concluded that for high-precision dosimetry such effects have to be taken into account. Nevertheless, the precise information about the dose response of the detector provided in this Monte Carlo study forms the basis of extracting directly the basic radiometric quantities photon fluence and photon energy fluence from the detector's signal using a deconvolution algorithm. The results are therefore promising for future application in absolute transit dosimetry and absolute dose reconstruction.

Biophysical Phenomena↗

PubMed2000

New computer procedure for routine EPR-dosimetry on tooth enamel: description and verification.

A software code was developed for fitting the EPR tooth enamel spectrum using linear combinations of Gaussian functions. The software is fastening EPR dose reconstruction for routine applications. The verification of the software was done comparing with the selective saturation method as an independent procedure of signal evaluation. Both methods were applied for the dose reconstruction of 13 teeth mostly from the Techa riverside. The evaluated doses by the two methods demonstrate an excellent agreement.

Dental Enamel↗

PubMed1996

Stability of the translocation frequency following whole-body irradiation measured in rhesus monkeys.

Chromosome translocations are persistent indicators of prior exposure to ionizing radiation and the development of 'chromosome painting' to efficiently detect translocations has resulted in a powerful biological dosimetry tool for radiation dose reconstruction. However, the actual stability of the translocation frequency with time after exposure must be measured before it can be used reliably to obtain doses for individuals exposed years or decades previously. Human chromosome painting probes were used here to measure reciprocal translocation frequencies in cells from two tissues of 8 rhesus monkeys (Macaca mulatta) irradiated almost three decades previously. Six of the monkeys were exposed in 1965 to whole-body (fully penetrating) radiation and two were unexposed controls. The primates were irradiated as juveniles to single doses of 0.56, 1.13, 2.00, or 2.25 Gy. Blood lymphocytes (and skin fibroblasts from one individual) were obtained for cytogenetic analysis in 1993, near the end of the animals' lifespans. Results show identical dose-response relationships 28 y after exposure in vivo and immediately after exposure in vitro. Because chromosome aberrations are induced with identical frequencies in vivo and in vitro, these results demonstrate that the translocation frequencies induced in 1965 have not changed significantly during the almost three decades since exposure. Finally, our emerging biodosimetry data for individual radiation workers are now confirming the utility of reciprocal translocations measured by FISH in radiation dose reconstruction.

Animals↗

PubMed2006

Around Semipalatinsk nuclear test site: progress of dose estimations relevant to the consequences of nuclear tests (a summary of 3rd Dosimetry Workshop on the Semipalatinsk nuclear test site area, RIRBM, Hiroshima University, Hiroshima, 9-11 of March, 2005).

The paper is an analytical overview of the main results presented at the 3rd Dosimetry Workshop in Hiroshima(9-11 of March 2005), where different aspects of the dose reconstruction around the Semipalatinsk nuclear test site(SNTS) were discussed and summarized. The results of the international intercomparison of the retrospective luminescence dosimetry(RLD) method for Dolon' village(Kazakhstan) were presented at the Workshop and good concurrence between dose estimations by different laboratories from 6 countries (Japan, Russia, USA, Germany, Finland and UK) was pointed out. The accumulated dose values in brick for a common depth of 10mm depth obtained independently by all participating laboratories were in good agreement for all four brick samples from Dolon' village, Kazakhstan, with the average value of the local gamma dose due to fallout (near the sampling locations) being about 220 mGy(background dose has been subtracted).Furthermore, using a conversion factor of about 2 to obtain the free-in-air dose, a value of local dose approximately 440 mGy is obtained, which supports the results of external dose calculations for Dolon': recently published soil contamination data, archive information and new models were used for refining dose calculations and the external dose in air for Dolon village was estimated to be about 500 mGy. The results of electron spin resonance(ESR) dosimetry with tooth enamel have demonstrated the notable progress in application of ESR dosimetry to the problems of dose reconstruction around the Semipalatinsk nuclear test site. At the present moment, dose estimates by the ESR method have become more consistent with calculated values and with retrospective luminescence dosimetry data, but differences between ESR dose estimates and RLD/calculation data were noted. For example mean ESR dose for eligible tooth samples from Dolon' village was estimated to be about 140 mGy(above background dose), which is less than dose values obtained by RLD and calculations. A possible explanation of the differences between ESR and RLD/calculations doses is the following: for interpretation of ESR data the "shielding and behaviour" factors for investigated persons should be taken into account. The "upper level" of the combination of "shielding and behaviour" factors of dose reduction for inhabitants of Dolon' village of about 0.28 was obtained by comparing the individual ESR tooth enamel dose estimates with the calculated mean dose for this settlement. The biological dosimetry data related to the settlements near SNTS were presented at the Workshop. A higher incidence of unstable chromosome aberrations, micronucleus in lymphocytes, nuclear abnormalities of thyroid follicular cells, T-cell receptor mutations in peripheral blood were found for exposed areas (Dolon', Sarjal) in comparison with unexposed ones(Kokpekty). The significant greater frequency of stable translocations (results of analyses of chromosome aberrations in lymphocytes by the FISH technique) was demonstrated for Dolon' village in comparison with Chekoman(unexposed village). The elevated level of stable translocations in Dolon' corresponds to a dose of about 180 mSv, which is close to the results of ESR dosimetry for this village. The importance of investigating specific morphological types of thyroid nodules for thyroid dosimetry studies was pointed out. In general the 3rd Dosimetry Workshop has demonstrated remarkable progress in developing an international level of common approaches for retrospective dose estimations around the SNTS and in understanding the tasks for the future joint work in this direction. In the framework of a special session the problems of developing a database and registry in order to support epidemiological studies around SNTS were discussed. The results of investigation of psychological consequences of nuclear tests, which are expressed in the form of verbal behaviour, were presented at this session as well.

Body Burden↗

PubMed2005

Intraoperative fluoroscopic dose assessment in prostate brachytherapy patients.

PURPOSE: To evaluate a fluoroscopy-based intraoperative dosimetry system to guide placement of additional sources to underdosed areas, and perform computed tomography (CT) verification. METHODS AND MATERIALS: Twenty-six patients with prostate carcinoma treated with either I-125 or Pd-103 brachytherapy at the Puget Sound VA using intraoperative postimplant dosimetry were analyzed. Implants were performed by standard techniques. After completion of the initial planned brachytherapy procedure, the initial fluoroscopic intraoperative dose reconstruction analysis (I-FL) was performed with three fluoroscopic images acquired at 0 (AP), +15, and -15 degrees. Automatic seed identification was performed and the three-dimensional (3D) seed coordinates were computed and imported into VariSeed for dose visualization. Based on a 3D assessment of the isodose patterns additional seeds were implanted, and the final fluoroscopic intraoperative dose reconstruction was performed (FL). A postimplant computed tomography (CT) scan was obtained after the procedure and dosimetric parameters and isodose patterns were analyzed and compared. RESULTS: An average of 4.7 additional seeds were implanted after intraoperative analysis of the dose coverage (I-FL), and a median of 5 seeds. After implantation of additional seeds the mean V100 increased from 89% (I-FL) to 92% (FL) (p < 0.001). In I-125 patients an improvement from 91% to 94% (p = 0.01), and 87% to 93% (p = 0.001) was seen for Pd-103. The D90 increased from 105% (I-FL) to 122% (FL) (p < 0.001) for I-125, and 92% (I-FL) to 102% (FL) (p = 0.008) for Pd-103. A minimal change occurred in the R100 from a mean of 0.32 mL (I-FL) to 0.6 mL (FL) (p = 0.19). No statistical difference was noted in the R100 (rectal volume receiving 100% of the prescribed dose) between the two techniques. The rate of adverse isodose patterns decreased between I-FL and FL from 42% to 8%, respectively. The I-125 patients demonstrated a complete resolution of adverse isodose patterns after the initial isodose reconstruction (I-FL). The Pd-103 patients demonstrated a final rate of 8% gaps, 0% islands, and 0% holes on corrected isodose reconstruction. CONCLUSION: The use of intraoperative fluoroscopy-based dose assessment can accurately guide in the implantation of additional sources to supplement inadequately dosed areas within the prostate gland. Additionally, guided implantation of additional source, can significantly improve V100s and D90s, without significantly increasing rectal doses.

Brachytherapy↗

PubMedDate not supplied

[The theory and practice of constructing calibration curves in biodozimetry].

The methodical peculiarities of experimental construction of regression "dose-effect" relationships used for the dose reconstruction are discussed. The method of computer simulations is applied to study the efficiency of different statistical procedures for plotting regression curves as well as the dependence of errors in dose prediction on the volume of examined material and on the choice of doses for a calibration curve. The causes of essential variability of calibrations obtained by different teams of researchers are discussed. A number of methodical recommendations is given for statistical processing of cytogenetic data. The procedure of constructing calibration dose dependence of the frequency of dicentrics on the basis experiments with in vitro gamma-irradiation of lymphocytes from blood samples of 5 donors is considered in detail. The expressions for statistical errors occurring in the dose reconstruction made on the base of the frequency of aberrations were derived and checked by the computer experiment.

Calibration↗

PubMed1998

Radiation exposure modeling for apartment living spaces with multiple radioactive sources.

Since late 1992, over 100 building complexes in Taiwan, including both public and private schools, and 1,000 apartments have been identified as emitting elevated levels of gamma-radiation. These high levels of gamma-radiation have been traced to construction steel contaminated with 60Co. Accurate reconstruction of the radiation exposure dosage among residents is complicated by the discovery of multiple radioactive sources within the living spaces and by the lack of comprehensive information about resident life-style and occupancy patterns within these contaminated spaces. The objective of this study was to evaluate the sensitivity of current dose reconstruction approach employed in an epidemiological study for the health effects of these occupants. We apply a statistical method of local smoothing in dose rate estimation and examine factors that are closely associated with radiation exposure from multiple radioactive sources in the apartment. Two examples are used, a simulated measurement in a hypothetical room with three radioactive sources and a real apartment in Ming-Shan Villa, one of the contaminated buildings. The simulated and estimated means are compared along 5-10 selected points of measurement: by local smoothing approach, with the furniture-adjusted space, and with the occupancy time-weighted mean. We found that the local smoothing approach came much closer to theoretical values. The local smoothing approach may serve as a refined method of radiation dose distribution modeling in exposure estimation. Before environmental exposure assessment, "highly occupied zones" (HOZs) in the contaminated spaces must be identified. Estimates of the time spent in these HOZs are essential to obtain accurate dosage values. These results will facilitate a more accurate dose reconstruction in the assessment of residential exposure in apartments with elevated levels of radioactivity.

Air Pollution, Radioactive↗