Internal Dose Estimates Research Articles

<sup>210</sup>Po and <sup>210</sup>Pb content in the certain types of foodstuffs. Optimization of the analytical method

An article contents the review of the data on the content of polonium and lead content: 210Po, 210Pb in natural entities, obtained from literary sources. The review is given of the existing methods for 210Po and 210Pb content investigation in different entities as well as the analysis of the expedience of the applying of the given polonium and lead content investigation in the foodstuffs technique for the use in a method under development of the radiochemical laboratory of the Institute. More perfect and simple for realization than existing method is given for 210Po and 210Pb content investigation in the foodstuffs from a sample with not more than 1.0 kg weight with minimal detectable activity not more than 0.01 Bq. The results are given of the investigation of 210Po and 210Pb content in the certain types of the foodstuffs sampled in the kitchen gardens located in Leningrad region and bought in the trade network of Saint-Petersburg. Estimation of potential average annual population internal exposure dose (Eint) is carried out due to 210Po and 210Pb content in the investigated foodstuffs which are consumed by the local population. For the estimation of the internal exposure doses we used the data on the food rations of adult population of the settlement of the city type according to the data of Rosstat and Internet-resources. It is demonstrated that population internal exposure dose even from several natural radionuclides taking into account consumption of a limited set of foodstuffs could exceed the exposure dose from artificial radionuclide in tens times even for the territories radioactively contaminated after the Chernobyl NPP accident.

The transfer of 239+240Pu, 241Am, 137Cs and 90Sr to the tissues of horses

Horses are important food sources in several countries however, data on their radionuclide uptake is less available than for many other farm animals. Information on the transfer of artificial radioisotopes from the environment to the food supply is necessary for internal dose assessment and assuring the safety of the population relying on this food source. This study provides data for a less studied farm animal and, in the case of 241Am and 239+240Pu, relatively poorly studied radionuclides with respect to transfer to animal products. The transfer parameters for 239+240Pu, 241Am, 137Cs and 90Sr to the organs of 1-year old fillies, 10-year old mares and through the placental barrier into foetuses were quantified after 60-days feeding with contaminated soil or diet contaminated by a leachate solution. The transfer of radionuclides from ingested soil to tissues was generally lower, by up to three orders of magnitude, than from a diet contaminated by a leachate solution. The ingestion of soil is a particularly important source of radionuclide intake to grazing animals in the Semipalatinsk Test Site. For 241Am there is a lack of available data, the two singular entries for mutton and beef in the IAEA handbook are higher than all values observed in the current study. The maximum observed transfer factor for 241Am was 72 ± 22*10−5 d kg−1 FW in the liver of the mare fed with leachate contaminated feed. For 239+240Pu the maximum transfer factor was 31.8 ± 8*10−5 d kg−1 FW observed also in the liver of the mare fed with leachate contaminated feed. The filly fed with leachate contaminated feed had the highest transfer parameter value for 137Cs, 35.3*10−3 d kg−1 FW. The highest 90Sr transfer factor was found in the ribs of the filly fed leachate contaminated feed, 720 ± 144 *10−3 d kg−1 FW. The results presented in this paper can be used to improve the current internal dose estimates from the ingestion of horse meat produced in the area, however they are based on a low sample size; future studies need to use a larger number of animals.

Estimation of internal dose from tap water after the Fukushima Daiichi Nuclear Power Station accident using newly obtained data.

Massive release of radioactive materials into the atmosphere occurred due to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in March 2011. The World Health Organization (WHO) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported the results of dose estimation to assess the health effect of the accident and both reports state that their assessments of internal and external exposure doses contain certain uncertainties due to uncertainties inherent to the basic data. Therefore, estimation of the internal dose from tap water was conducted in this study by utilizing a database of deposition calculated by an atmospheric transfer, dispersion and deposition model (ATDM) in conjunction with the newly obtained data on the volume of daily water intake obtained by a web-based survey. The median mean and 95-percentile of thyroid equivalent doses were estimated for 1-year and 10-year children and adults in 12 municipalities in the evacuation area in Fukushima prefecture. The present mean thyroid dose estimations for 1-year children (0.4–16.2 mSv) are smaller than the corresponding values in the UNSCEAR 2013 report (1.9–49 mGy). Dose-modifying factors in the Japanese or local community are discussed.

Cancer risk estimation of glycidol based on rodent carcinogenicity studies, a multiplicative risk model and in vivo dosimetry

Here we evaluate a multiplicative (relative) risk model for improved cancer risk estimation of genotoxic compounds. According to this model, cancer risk is proportional to the background tumor incidence and to the internal dose of the genotoxic compound. Furthermore, the relative risk coefficient per internal dose is considered to be approximately the same across tumor sites, sex, and species.In the present study, we demonstrate that the relative risk model is valid for cancer risk estimation of glycidol, a common food contaminant. Published tumor data from glycidol carcinogenicity studies in mice and rats were evaluated in combination with internal dose estimates from hemoglobin adduct measurements in blood from mice and rats treated with glycidol in short-term studies. A good agreement between predicted and observed tumor incidence in responding sites was demonstrated in the animals, supporting a relative risk coefficient that is independent of tumor site, sex, and species. There was no significant difference between the risk coefficients for mice (5.1% per mMh) and rats (5.4% per mMh) when considering internal doses of glycidol. Altogether, this mechanism-based risk model gives a reliable risk coefficient, which then was extrapolated to humans considering internal dose, and background cancer incidence.

Verification of Harmonization of Dose Assessment Results According to Internal Exposure Scenarios

Background: The determination of the amount of radionuclides and internal dose for the worker who may have intake of radionuclides results in a variation due to uncertainty of measurement data and ingestion information. As a result of this, it is possible that for the same internal exposure scenario assessors could make considerably different estimation of internal dose. In order to reduce this difference, internal exposure scenarios for nuclear facilities were developed, and intercomparison were made to determine the harmonization of dose assessment results among the assessors. Materials and Methods: Seven cases on internal exposures incidents that have occurred or may occur were prepared by referring to the intercomparison excercise scenario that NRC and IAEA have carried out. Based on this, 16 nuclear facilities concerned with internal exposure in Korea were asked to evaluate the scenarios. Each result was statistically determined according to the harmonization discrimination criteria developed by IDEAS/IAEA. Results and Discussion: The results were evaluated as having no outliers in all 7 cases. However, the distribution of the results was spread by various causes. They can be divided into two wide categories. The first one is the distribution of the results according to the assumption of the intake factors and the evaluation factors. The second one is distribution due to misapplication of calculation method and factors related to internal exposure. Conclusion: In order to satisfy the harmonization criteria and accuracy of the internal exposure dose evaluation, it is necessary that exact guidelines should be set on low dose, and various intercomparison cases also be needed including high dose exposure as well as the specialized education. The aim of the blind test is to make harmonization evaluation, but it will also contribute to securing the expertise and high quality of dose evaluation data through the discussion among the participants.

Development of Prototype Iranian male pelvic phantom for internal dosimetry

Introduction: Existing phantoms have been constructed based on Caucasian, non-Caucasian and race-specific datasets. According to previous studies made efforts to present Korean- specific phantoms and Chinese female phantom based on CVH dataset due to compare the resulting internal dosimetry with the Caucasian based data showed possible racial difference in human anatomy between Caucasian and non- Caucasian populations. These phantoms have been used for internal radionuclide dosimetry and other nuclear-medicine applications. Specific absorbed fractions (SAF) are tools for internal dose estimation of radionuclide intake. The differences were due to the racial and anatomical differences in organ mass and inter-organ distance. Many studies have been tried to provide an accurate and reliable data for internal radiation dose calculations. Therefor we construct an Iranian computational phantom to evaluate radiation dose organs within male pelvic region based on Iranian datasets. Internal dosimetry on organ is getting more important from the viewpoint of radiation protection of organ at risk. Materials and Methods: The first version of computational Iranian male pelvis phantom(PIPM) is provided by 5 MRI datasets of Iranian male for precise organ dose calculation, at first organs within pelvic region are segmented by enhancing their margins in each slice, determination of organs volume then, prototype Iranian male pelvis phantom was developed by modifying the equation of internal organs of the ORNL adult phantom finally, this phantom was imported to general purpose Monte Carlo code to simulate photon transport from internal radiation source. Results: The results showed that the individual comparable phantom can be calculated with acceptable accuracy using geometric registration. Comparison of dose calculation for Iranian male pelvic, MIRD and RADAR phantoms showed that differences of self-SAF were affected by organ volume differences. The average of the percent SAF deviation was calculated in testes organ -7.73%, -5.53% for PIMP phantom into MIRD and RADAR phantoms respectively. The largest deviation was observed in urinary bladder organ follow as 37.3%, 52.3% into MIRD and RADAR phantoms and it is shown -23.5% variations in self-SAF prostate organ into MIRD phantom. This phantom could be used for absorbed dose calculation of Iranian male pelvic region with acceptable accuracy in nuclear medicine. Conclusion: A prototype computational Iranian adult male pelvis phantom was represented from 5 Iranian adult males; the results showed that comparable phantom can be calculated internal absorbed dose with significant differences. Accurate voxel phantom is needed for dosimetric simulation in nuclear medicine for malignant tumors in male pelvic region. However, most of the existing voxel phantoms are constructed on the basis of Caucasian or non-Chinese population. It might be provided first Iranian male reference volume organ dataset for future researches.

Development of a stochastic biokinetic method and its application to internal dose estimation for insoluble cesium-bearing particles

ABSTRACT Spherical cesium-bearing particles were found around the Fukushima Daiichi Nuclear Power Plant after its accident. These particles are insoluble with high specific activities. If such a particle is incorporated into the body, it is expected that the radioactive cesium contained in the particle will move as a single particulate material without being distributed throughout the body. Consequently, internal doses vary depending on the pathway of the particle in the body. Therefore, general deterministic methods for dose estimation are not applicable to the intake of small number of cesium-bearing particles. In this study, a Monte Carlo method was developed to evaluate a probability density function of internal doses for inhalation of a particulate material. In addition, a biokinetic model was constructed to consider the insolubility of the particles. Probability density functions of committed equivalent and effective doses were estimated using the constructed biokinetic model with the developed computation method. As a result, the uncertainty of the doses was very large for single particle inhalation. However, it was observed that this uncertainty decreased with increasing number of simultaneously inhaled particles. On the other hand, the consideration about the insolubility made the doses somewhat higher than those based on the general cesium model.

Internal doses from radionuclides and their health effects following the Fukushima accident

This paper presents an overview of current internal dose estimates from the Fukushima accident, potential population specific uncertainties in these estimates are investigated, along with the relative effects of internal and external exposures. Thyroid doses were largely due to 131I, but variations in thyroid weight and fractional uptake and retention times of 131I in the thyroid contribute to uncertainties in thyroid dose estimates. Lower values for these parameters in the Japanese population, as compared to international reference assumptions, would lead to underestimation of doses on the basis of reference thyroid weights and overestimation of doses using reference thyroid uptake and retention times. Any overall bias in thyroidal doses due to population specific factors is the net result of the balance between these effects. Internal doses to other organs are largely due to 134Cs and 137Cs and their whole body distribution, population specific differences in these dose estimates are driven by average body mass, due to the inverse relationship between this and retention times. Potential differences in dose estimates and any inferred risks, due to local population specific factors, may be less than a factor of two for children and male adults, but the potential difference may be slightly underestimated for female adults. Recent micro-dosimetric studies have confirmed the existing perception that risk from internal exposures to 137Cs, 134Cs, and 131I should be nearly equivalent to that from external exposure to gamma rays at the same absorbed dose. Epidemiological studies provide comparisons between external and internal exposures to 131I in children and suggest that effects of internal exposure are similar to those of external exposure. Effective dose has been formulated to harmonise internal and external exposure risks for radiation protection purposes. On the basis of this review, the use of effective dose in this context does not seem to be unreasonable.

OA249] Experimental validation of a Monte Carlo code for internal breast dosimetry in mammography

Purpose To validate Monte Carlo (MC) simulations in absolute terms at the local dose deposition level for breast dosimetry applications using new experimental methodologies. Methods Three types of dose measurement devices were used for this study; thermoluminescent dosimeters (TLD-100H), metal oxide semiconductor field-effect transistor dosimeters (MOSFET, model TN-1002RD), and GafChromicTM films (model XR-QA2). First, experimental methodologies were developed and the performance of each of the three dosimeter technologies tested using a monoenergetic synchrotron-based setup. For validation under clinical conditions, a clinical digital mammography system (Mammomat INSPIRATION, Siemens Healthcare, Forchheim, Germany) and two phantoms, a semi-cylindrical homogeneous 50% glandular density phantom, and a heterogeneous anthropomorphic breast phantom, were used. MC simulations reproducing the experimental conditions were performed using code based on the Geant4 toolkit. Experimental and simulated 2D-dose maps and dose profiles for different depths in the axial-phantom plane were compared. Results The dosimeters have an energy-dependent response (it increases by ∼ 48% for XR-QA2 films and by ∼ 37% for MOSFET in the energy interval 18–28 keV), resulting in the need for calibration at each phantom depth to be investigated to obtain accurate measurements. The developed experimental methodologies allow for dose measurements with uncertainty levels of ∼ 5% (one combined standard uncertainty) at the entrance surface, up to ∼ 9% 4 cm deep inside the phantom. This increase in uncertainty is due to the decrease in dose with increasing phantom depth, which is reduced by 93% after 4 cm of the homogeneous phantom. In a heterogeneous background, dosimeters are able to detect local dose gradients of up to 46% between the boundaries of two materials. The MC-based estimates of the dose matched, to within one combined standard uncertainty, with the experimental ones for all three dosimeters technologies and for all tested depths. Conclusions The developed experimental methodologies allow for internal breast dose estimation with good accuracy. These procedures could be successfully applied to validate MC code at the local dose level and in absolute terms. The validation in a heterogeneous, anthropomorphic breast phantom is crucial to the development of a new breast model and dosimetry method.

Development and Validation of an Analytical Method to Quantitate Tris(chloroisopropyl)phosphate in Rat and Mouse Plasma using Gas Chromatography with Flame Photometric Detection.

Tris(chloropropyl)phosphate (TCPP) is an organophosphorus flame retardant (OPFR) and plasticizer increasingly used in consumer products and as a replacement for brominated flame retardants. Commercially available TCPP is a mixture of four structural isomers the most abundant of which is tris(1-chloro-2-propyl)phosphate (TCPP-1). Although there is a widespread use of TCPP and potential for human exposure, there is limited data on the safety or toxicity of TCPP. The National Toxicology Program is conducting long-term studies to examine the toxicity of the TCPP in rats after lifetime exposure, including perinatal oral exposure. Quantitative estimates of internal dose are essential to interpret toxicological findings in rodents. To aid in this, a method was fully validated to quantitate the most abundant isomer, TCPP-1, in female Harlan Sprague Dawley (HSD) rat and B6C3F1 mouse plasma with partial validation in male rat plasma, and male and female mouse plasma. The method used protein precipitation using trichloroacetic acid followed by the extraction with toluene, and analysis by gas chromatography with flame photometric detection. The performance of the method was evaluated over 5-70 ng TCPP-1/mL plasma. The method was linear (r ≥ 0.99), accurate (inter-day relative error: ≤ ± -7.2) and precise (inter-batch relative standard deviation: ≤27.5%). The validated method has lower limits of quantitation and detection of ~5 and 0.9 ng/mL, respectively, in female HSD rat plasma and can be used on samples as small as 50 μL demonstrating the applicability to plasma samples from toxicology studies.

Individualized adjustments to reference phantom internal organ dosimetry—scaling factors given knowledge of patient external anatomy

Internal radiation dose estimates for diagnostic nuclear medicine procedures are typically calculated for a reference individual. Resultantly, there is uncertainty when determining the organ doses to patients who are not at 50th percentile on either height or weight. This study aims to better personalize internal radiation dose estimates for individual patients by modifying the dose estimates calculated for reference individuals based on easily obtainable morphometric characteristics of the patient. Phantoms of different sitting heights and waist circumferences were constructed based on computational reference phantoms for the newborn, 10 year-old, and adult. Monoenergetic photons and electrons were then simulated separately at 15 energies. Photon and electron specific absorbed fractions (SAFs) were computed for the newly constructed non-reference phantoms and compared to SAFs previously generated for the age-matched reference phantoms. Differences in SAFs were correlated to changes in sitting height and waist circumference to develop scaling factors that could be applied to reference SAFs as morphometry corrections. A further set of arbitrary non-reference phantoms were then constructed and used in validation studies for the SAF scaling factors. Both photon and electron dose scaling methods were found to increase average accuracy when sitting height was used as the scaling parameter (~11%). Photon waist circumference-based scaling factors showed modest increases in average accuracy (~7%) for underweight individuals, but not for overweight individuals. Electron waist circumference-based scaling factors did not show increases in average accuracy. When sitting height and waist circumference scaling factors were combined, modest average gains in accuracy were observed for photons (~6%), but not for electrons. Both photon and electron absorbed doses are more reliably scaled using scaling factors computed in this study. They can be effectively scaled using sitting height alone as patient-specific morphometric parameter.

Tritium internal dose estimation from measurements with liquid scintillators

Tritium may exist in several chemical and physical forms in workplaces, common occurrences are in vapor or liquid form (as tritiated water) and in organic form (e.g. thymidine) which can get into the body by inhalation or by ingestion. For internal dose assessment it is usually assumed that urine samples for tritium analysis are obtained after the tritium concentration inside the body has reached equilibrium following intake. Comparison was carried out for two types of vials, two efficiency calculation methods and two available liquid scintillation devices to highlight the errors of the measurements. The results were used for dose estimation with MONDAL-3 software. It has been shown that concerning the accuracy of the final internal dose assessment, the uncertainties of the assumptions used in the dose assessment (for example the date and route of intake, the physical and chemical form) can be more influential than the errors of the measured data. Therefore, the improvement of the experimental accuracy alone is not the proper way to improve the accuracy of the internal dose estimation.

Internal breast dosimetry in mammography: Experimental methods and Monte Carlo validation with a monoenergetic x-ray beam.

To investigate the performance, such as energy dependence and sensitivity, of thermoluminescent dosimeters (TLD), metal oxide semiconductor field-effect transistor dosimeters (MOSFET), and GafChromic™ films, and to validate the estimates of local dose deposition of a Monte Carlo (MC) simulation for breast dosimetry applications. Experimental measurements were performed using a monoenergetic beam at the ELETTRA synchrotron radiation light source (Trieste, Italy). The three types of dosimeters were irradiated in a plane transversal to the beam axis and calibrated in terms of air kerma. The sensitivity of MOSFET dosimeters and GafChromic™ films was evaluated in the range of 18-28 keV. Three different calibration curves for the GafChromic™ films were tested (logarithmic, rational, and exponential functions) to evaluate the best-fit curve in the dose range of 1-20 mGy. Internal phantom dose measurements were performed at 20 keV for four different depths (range 0-3 cm, with 1 cm steps) using a homogeneous 50% glandular breast phantom. A GEANT4 MC simulation was modified to match the experimental setup. Thirty sensitive volumes, on the axial-phantom plane were included at each depth in the simulation to characterize the internal dose variation and compare it to the experimental TLD and MOSFET measurements. Experimental 2D dose maps were obtained with the GafChromic™ films and compared to the simulated 2D dose distributions estimated with the MC simulations. The sensitivity of the MOSFET dosimeters and GafChromic™ films increased with x-ray energy, by up to 37% and 48%, respectively. Dose-response curves for the GafChromic™ film result in an uncertainty lower than 5% above 6 mGy, when a logarithmic relationship is used in the dose range of 1-10 mGy. All experimental values fall within the experimental uncertainty and a good agreement (within 5%) is found against the MC simulation. The dose decreased with increasing phantom depth, with the reduction being ~80% after 3 cm. The uncertainty of the empirical measurements makes the experimental values compatible with a flat behavior across the phantom slab for all the investigated depths, while the MC points to a dose profile with a maximum toward the center of the phantom. The calibration procedures and the experimental methodologies proposed lead to good accuracy for internal breast dose estimation. In addition, these procedures can be successfully applied to validate MC codes for breast dosimetry at the local dose level. The agreement among the experimental and MC results not only shows the correctness of the empirical procedures used but also of the simulation parameters.

Circulatory disease in French nuclear fuel cycle workers chronically exposed to uranium: a nested case–control study

ObjectivesThere is growing evidence of an association between low-dose external γ-radiation and circulatory system diseases (CSDs), yet sparse data exist about an association with chronic internal uranium exposure and the...

Риск рака щитовидной железы после воздействия I-131: объединенный анализ экспериментальных и эпидемиологических данных за семь десятилетий. Cообщение 2. Обзор методов внутренней дозиметрии и определения поглощенной дозы облучения щитовидной железы

Риск рака щитовидной железы после воздействия I-131: объединенный анализ экспериментальных и эпидемиологических данных за семь десятилетий. Cообщение 2. Обзор методов внутренней дозиметрии и определения поглощенной дозы облучения щитовидной железы

Development of probabilistic internal dosimetry computer code

Internal radiation dose assessment involves biokinetic models, the corresponding parameters, measured data, and many assumptions. Every component considered in the internal dose assessment has its own uncertainty, which is propagated in the intake activity and internal dose estimates. For research or scientific purposes, and for retrospective dose reconstruction for accident scenarios occurring in workplaces having a large quantity of unsealed radionuclides, such as nuclear power plants, nuclear fuel cycle facilities, and facilities in which nuclear medicine is practiced, a quantitative uncertainty assessment of the internal dose is often required. However, no calculation tools or computer codes that incorporate all the relevant processes and their corresponding uncertainties, i.e., from the measured data to the committed dose, are available. Thus, the objective of the present study is to develop an integrated probabilistic internal-dose-assessment computer code. First, the uncertainty components in internal dosimetry are identified, and quantitative uncertainty data are collected. Then, an uncertainty database is established for each component. In order to propagate these uncertainties in an internal dose assessment, a probabilistic internal-dose-assessment system that employs the Bayesian and Monte Carlo methods. Based on the developed system, we developed a probabilistic internal-dose-assessment code by using MATLAB so as to estimate the dose distributions from the measured data with uncertainty. Using the developed code, we calculated the internal dose distribution and statistical values (e.g. the 2.5th, 5th, median, 95th, and 97.5th percentiles) for three sample scenarios. On the basis of the distributions, we performed a sensitivity analysis to determine the influence of each component on the resulting dose in order to identify the major component of the uncertainty in a bioassay. The results of this study can be applied to various situations. In cases of severe internal exposure, the causation probability of a deterministic health effect can be derived from the dose distribution, and a high statistical value (e.g., the 95th percentile of the distribution) can be used to determine the appropriate intervention. The distribution-based sensitivity analysis can also be used to quantify the contribution of each factor to the dose uncertainty, which is essential information for reducing and optimizing the uncertainty in the internal dose assessment. Therefore, the present study can contribute to retrospective dose assessment for accidental internal exposure scenarios, as well as to internal dose monitoring optimization and uncertainty reduction.

The impact of variation in scaling factors on the estimation of internal dose metrics: a case study using bromodichloromethane (BDCM)

A rate for hepatic metabolism (Vmax) determined in vitro must be scaled for in vivo use in a physiologically based pharmacokinetic (PBPK) model. This requires the use of scaling factors such as mg of microsomal protein per gram of liver (MPPGL) and liver mass (FVL). Variation in MPPGL and FVL impacts variation in Vmax, and hence PBPK model-derived estimates of internal dose used in dose response analysis. The impacts of adult human variation in MPPGL and FVL on estimates of internal dose were assessed using a human PBPK model for bromodichloromethane (BDCM), a water disinfection byproduct, for multiple internal dose metrics for two exposure scenarios (single 0.25 liter drink of water or 10 min shower) under plausible (5 μg/L) and high level (20 μg/L) water concentrations. For both concentrations, all internal dose metrics were changed less than 5% for the showering scenario (combined inhalation and dermal exposure). In contrast, a 27-fold variation in area under the curve (AUC) for BDCM in venous blood was observed at both oral exposure concentrations, whereas total amount of BDCM metabolized in liver was relatively unchanged. This analysis demonstrates that variability in the scaling factors used for in vitro to in vivo extrapolation (IVIVE) for metabolic rate parameters can have a significant route-dependent impact on estimates of internal dose under environmentally relevant exposure scenarios. This indicates the need to evaluate both uncertainty and variability for scaling factors used for IVIVE.

Application Of 99m Tc Radioisotope In Diagnostic Procedures And Internal Radiation Dose Estimation

At about 70% of nuclear medicine procedures have utilized <sup>99m</sup>Tc in their clinical practices.This has lead <sup>99m</sup>Tc becoming the most convenient radioisotope in nuclear medicine diagnostic. To estimate the internal radiation dose due to the administration of <sup>99m</sup>Tc to the patients, only few documents from International Commission of Radiation Protection (ICRP) have been available. However, the calculation usually has applied Caucasian data in Standard Reference Man as a model. The objective of this study was to review the application of <sup>99m</sup>Tc in Indonesia and to compare the internal dose estimation for <sup>99m</sup>Tc procedures by using Organ Level Internal Dose Assessment/ EXponential Modeling (OLINDA/EXM) software. The result of calculation was compared between Adult Caucasian model and Asian Reference Man. The result shows that <sup>99m</sup>Tc has been well applied and developed for diagnostic procedures in Nuclear Medicine Department. Moreover, in most diagnostic procedures using <sup>99m</sup>Tc in Indonesia, adult patients will receive effective dose about 1-15% higher than adult patient in foreign countries which apply the Caucasian model. Hence, to estimate the similar stochastic risk from the same procedure, the maximum value in recommended administered dose should be avoided and need to be evaluated.

NUMERICAL SIMULATION OF DIRECT MEASUREMENT TO DETERMINE THYROID 131I CONTENT OF TWO TEPCO WORKERS CONSIDERING INDIVIDUAL TISSUE THICKNESS.

After the Fukushima Daiichi Nuclear Power Station accident, the National Institute of Radiological Sciences examined seven heavily exposed emergency workers and performed internal dose estimations. The largest dose contributor was found to be (131)I, which was detected by thyroid monitor with an HPGe detector. Different energy peaks from (131)I were simultaneously identified in the pulse-height spectra of the two subjects with the highest doses regardless of late measurements. A closer look at the spectra indicated that the count ratio of the two peak areas at 80.2 and 365 keV differed somewhat between the individual workers, suggesting a difference in attenuation in the overlaying soft tissue and in the thyroid itself. In this study, the relationship between the count ratio (80.2/365 keV) and the thickness of soft tissue overlying the thyroid was investigated by means of numerical simulations performed using the Japanese Male (JM) phantom varying the thickness of the overlaying tissue. From the measured count ratios, it was possible to estimate that the overlaying tissue was thinner for Worker 1 (difference from the JM phantom: -0.34±1.29 cm) and thicker for Worker 2 (diff.: 2.5±1.2 cm). The thyroid (131)I contents evaluated taking into account the individual thicknesses were 4.3 kBq for Worker 1 and 8.4 kBq for Worker 2, resulting in a significant increase for Worker 2 compared with the content based on the default counting efficiency at 365 keV of the original JM phantom. However, the results have large uncertainty factors of 1.4 for Worker 1 and 1.3 for Worker 2 and should be carefully considered together with other factors influencing the attenuation.

Using physiologically based pharmacokinetic modeling and benchmark dose methods to derive an occupational exposure limit for N-methylpyrrolidone

The developmental effects of NMP are well studied in Sprague–Dawley rats following oral, inhalation, and dermal routes of exposure. Short-term and chronic occupational exposure limit (OEL) values were derived using an updated physiologically based pharmacokinetic (PBPK) model for NMP, along with benchmark dose modeling. Two suitable developmental endpoints were evaluated for human health risk assessment: (1) for acute exposures, the increased incidence of skeletal malformations, an effect noted only at oral doses that were toxic to the dam and fetus; and (2) for repeated exposures to NMP, changes in fetal/pup body weight. Where possible, data from multiple studies were pooled to increase the predictive power of the dose–response data sets. For the purposes of internal dose estimation, the window of susceptibility was estimated for each endpoint, and was used in the dose–response modeling. A point of departure value of 390 mg/L (in terms of peak NMP in blood) was calculated for skeletal malformations based on pooled data from oral and inhalation studies. Acceptable dose–response model fits were not obtained using the pooled data for fetal/pup body weight changes. These data sets were also assessed individually, from which the geometric mean value obtained from the inhalation studies (470 mg*hr/L), was used to derive the chronic OEL. A PBPK model for NMP in humans was used to calculate human equivalent concentrations corresponding to the internal dose point of departure values. Application of a net uncertainty factor of 20–21, which incorporates data-derived extrapolation factors, to the point of departure values yields short-term and chronic occupational exposure limit values of 86 and 24 ppm, respectively.