Organ dose reconstruction for the radiation epidemiological study of Korean radiation workers: the first dose evaluation for the Korean Radiation Worker Study (KRWS).

The Korea Institute of Radiological and Medical Sciences has started a radiation epidemiological study, titled "Korean Radiation Worker Study," to evaluate the health effects of occupational exposure to radiation. As a part of this study, we investigated the methodologies and results of reconstructing organ-specific absorbed doses based on personal dose equivalent, Hp(10), reported from 1984 to 2019 for 20,605 Korean radiation workers. For the organ dose reconstruction, representative exposure scenarios (i.e., radiation energy and exposure geometry) were first determined according to occupational groups, and dose coefficients for converting Hp(10) to organ absorbed doses were then appropriately taken based on the exposure scenarios. Individual annual doses and individual cumulative doses were reconstructed for 27 organs, and the highest values were observed in the thyroid doses (on average 0.77 mGy/y and 10.47 mGy, respectively). Mean values of individual cumulative absorbed doses for the red bone marrow, colon, and lungs were 7.83, 8.78, and 8.43 mSv, respectively. Most of the organ doses were maximum for industrial radiographers, followed by nuclear power plant workers, medical workers, and other facility workers. The organ dose database established in this study will be utilized for organ-specific risk estimation in the Korean Radiation Worker Study.

Uncertainty quantification of bioassay functions for the internal dosimetry of radioiodine.

Bioassay functions, which are provided by the International Commission on Radiological Protection, are used to estimate the intake activity of radionuclides; however, they include considerable uncertainties in terms of the internal dosimetry for a particular individual. During a practical internal dose assessment, the uncertainty in the bioassay function is generally not introduced because of the difficulty in quantification. Therefore, to clarify the existence of uncertainty in the bioassay function and provide dosimetrists with an insight into this uncertainty, this study attempted to quantify the uncertainty in the thyroid retention function used for radioiodine exposure. The uncertainty was quantified using a probabilistic estimation of the thyroid retention function through the propagation of the distribution of biokinetic parameters by the Monte Carlo simulation technique. The uncertainties in the thyroid retention function, expressed in terms of the scattering factor, were in the ranges of 1.55-1.60 and 1.40-1.50 for within 24 h and after 24 h, respectively. In addition, the thyroid retention function within 24 h was compared with actual measurement data to confirm the uncertainty due to the use of first-order kinetics in the biokinetic model calculation. Significantly higher thyroid uptakes (by a factor of 1.9) were observed in the actual measurements. This study indicates that consideration of the uncertainty in the thyroid retention function can avoid a significant over- and under-estimation of the internal dose, particularly when a high dose is predicted.

Evaluation of performance characteristics of portal monitor for radiation emergency.

For evaluating the counting efficiency of a portal monitor, we use a137Cs radiation point source (1 µCi) to subsequently establish it effective measurable area. Through simulation, we estimate the appropriate distance from potentially contaminated individuals in the scanning queue to the monitoring individual. When this distance is over 10 m, the counting efficiency was below 0.01%. We find that the triage can be applied to roughly 180 individuals per hour during mass casualties.

Health effects of exposure to radon: implications of the radon bed mattress incident in Korea.

Radon is a naturally occurring radioactive material formed by the slow decay of uranium and thorium found in the earth's crust or construction materials. Internal exposure to radon accounts for about half of the natural background radiation dose to which humans are exposed annually. Radon is a carcinogen and is the second leading cause of lung cancer following smoking. An association between radon and lung cancer has been consistently reported in epidemiological studies on mine workers and the general population with indoor radon exposure. However, associations have not been clearly established between radon and other diseases, such as leukemia and thyroid cancer. Radiation doses are assessed by applying specific dose conversion coefficients according to the source (e.g., radon or thoron) and form of exposure (e.g., internal or external). However, regardless of the source or form of exposure, the effects of a given estimated dose on human health are identical, assuming that individuals have the same sensitivity to radiation. Recently, radiation exceeding the annual dose limit of the general population (1 mSv/yr) was detected in bed mattresses produced by D company due to the use of a monazite-based anion powder containing uranium and thorium. This has sparked concerns about the health hazards for mattress users caused by radiation exposure. In light of this event, this study presents scientific information about the assessment of radon and thoron exposure and its human implications for human health, which have emerged as a recent topic of interest and debate in society.

Screening Criteria for the General Public in Radiation Emergencies From Liquid Scintillation Urinalysis.

Gross alpha/beta screening of urine samples was performed to evaluate internal contamination and dose assessment. Data on background radioactivity concentration were extracted by analyzing the urine samples of non-contaminated individuals who had visited a radiation effect medical clinic since 2012. Screening criteria were studied and established for radiation emergencies based on these results. In particular, pure beta-emitting radionuclides (H and Sr) with a high dose conversion factor were considered to be the source of contamination. Moreover, the screening criteria for the general public were determined based on age groups. The liquid scintillation counting method was used for gross alpha/beta radiation counting. A standardized procedure of correction for chemical and color quenching was performed and validated. The gross beta counting method was validated by analyzing standard urine samples. The fluctuation of the screening criteria was large, based on the time elapsed after intake. A screening criterion of 150 Bq L can be applied within 5 d after intake considering the minimum detectable activity. A standard screening criterion set to 250 Bq L will be used as an important reference for decision making and additional monitoring. Although early evaluation and accurate identification of contaminated radionuclides is preferred, these relatively simple criteria were proposed to address radiation emergency situations involving several casualties.

RAPID MONITORING OF INTERNAL CONTAMINATION USING A MOBILE RADIOBIOASSAY LABORATORY FOLLOWING RADIATION EMERGENCIES.

In any radiation emergency, it may be necessary to monitor large numbers of people for internal contamination resulting from inhalation/ingestion of radionuclides released from the accident. The National Radiation Emergency Medical Center of the Korea Institute of Radiological and Medical Sciences constructed a mobile radiobioassay laboratory for rapid field-based monitoring of internal contamination. The main features of the mobile laboratory were designed and the results of performance were tested for rapid monitoring in this paper. We found that maximum throughput for internal contamination monitoring using the whole body counter installed in the laboratory was about 200 people per day. The minimum detectable activities were estimated for the in-vivo and in-vivo radiobioassay systems in the mobile unit. This mobile unit will improve the population monitoring capabilities for internal contamination of individuals affected following nuclear or radiological emergencies.

Rapid Analysis of 239,238Pu, 241Am, and 90Sr for Nasal Smear Samples in Radiation Emergency and Evaluation of Intake Retention Fraction.

The efficiency of the nasal smear method was reviewed to perform a method of sample collection, analysis and initial dose estimation. The screening method of alpha-emitting radionuclides using chemical separation and alpha spectrometry was also studied. To rapidly conduct the appropriate response to victims, special monitoring for Pu, Am, and Sr using sequential analysis was established, and the method was successfully validated through participation in an international inter-comparison program. The duration of the analysis method was evaluated with regard to application in emergency situations because of its relatively rapid treatment and counting time. The intake retention fraction was calculated and evaluated to review the characteristics of each radionuclide in the anterior nasal passage of the extra-thoracic region. No large difference was observed among the four radionuclides. However, the values of the intake retention fraction were affected by age groups because of the different respiratory rates. The effects of the Y ingrowth and particle size were also discussed.

Monitoring and Dose Assessment for Children Following a Radiation Emergency Part I: Reference Values for In Vitro Bioassay.

Following a radiation emergency, children may be internally contaminated by the radionuclide(s) involved. Timely assessment of the contamination informs the need for medical treatment for those persons who had significant intakes and reassures those whose intakes are not a medical concern. In vitro bioassay reference values for children of all ICRP age groups are derived for 30 contamination scenario/radionuclide combinations involving 13 radionuclides. These bioassay values are derived from an intake that leads to a 70-y committed effective dose of 50 mSv or a 30-d RBE-weighted absorbed dose to the lungs of 0.2 Gy-Eq, depending on which criterion is more strict. These values are presented in a collection of lookup tables that can be used directly as references.

Estimates of Radiation Doses and Cancer Risk from Food Intake in Korea.

The aim of this study was to estimate internal radiation doses and lifetime cancer risk from food ingestion. Radiation doses from food intake were calculated using the Korea National Health and Nutrition Examination Survey and the measured radioactivity of (134)Cs, (137)Cs, and (131)I from the Ministry of Food and Drug Safety in Korea. Total number of measured data was 8,496 (3,643 for agricultural products, 644 for livestock products, 43 for milk products, 3,193 for marine products, and 973 for processed food). Cancer risk was calculated by multiplying the estimated committed effective dose and the detriment adjusted nominal risk coefficients recommended by the International Commission on Radiation Protection. The lifetime committed effective doses from the daily diet are ranged 2.957-3.710 mSv. Excess lifetime cancer risks are 14.4-18.1, 0.4-0.5, and 1.8-2.3 per 100,000 for all solid cancers combined, thyroid cancer, and leukemia, respectively.

Retrospective biodosimetry using translocation frequency in a stable cell of occupationally exposed to ionizing radiation.

Two cases of hematological malignancies were reported in an industrial radiography company over a year, which were reasonably suspected of being consequences of prolonged exposure to ionizing radiation because of the higher incidence than expected in the general population. We analyzed chromosomal aberrations in the peripheral blood lymphocytes from the other workers who had been working under similar circumstances as the patients in the company. Among the subjects tested, 10 workers who belonged to the highest band were followed up periodically for 1.5 years since the first analysis. The aim of this study was to clarify pertinence of translocation analysis to an industrial set-up where chronic exposure was commonly expected. To be a useful tool for a retrospective biodosimetry, the aberrations need to be persistent for a decade or longer. Therefore we calculated the decline rates and half-lives of frequency for both a reciprocal translocation and a dicentric chromosome and compared them. In this study, while the frequency of reciprocal translocations was maintained at the initial level, dicentric chromosomes were decreased to 46.9% (31.0-76.5) of the initial frequency over the follow-up period. Our results support the long-term stability of reciprocal translocation through the cell cycle and validate the usefulness of translocation analysis as a retrospective biodosimetry for cases of occupational exposure.

Screening of alpha- and beta-emitting radionuclides using liquid scintillation counting and monitoring procedures in radiation emergencies.

Urine gross alpha and beta activity analysis was conducted, and an internal contamination screening method was adopted to monitor visitors to Japan after the Fukushima accident. In particular, spot urine samples were used to evaluate internal contamination for 16 mo, and a total of 90 people participated in gross alpha and beta emitter screening. An ultra-low-background liquid scintillation counter was used for measurement, and optimal pulse shape analysis values were determined by measuring alpha- and beta-emitting certified reference materials. Moreover, linearity and reproducibility were assessed to validate the adopted methods, and international intercomparison was conducted using synthetic urine samples by measuring alpha- and beta-emitting radionuclides in multi-contaminated samples. Here, the measurement results of visitors to Japan are discussed, and a screening procedure is established for gross alpha and beta activity analysis during radiation emergencies.