Estimation of the historical radiation dose of Korean radiation workers, 1961-1983.

Accurate dosimetry plays a key role in evaluating the radiation-induced health risks of radiation workers. The National Dose Registry in Korea contains the dose records of radiation workers in nuclear-related occupations since 1984. Thus, radiation doses for workers before 1984 are often sparse or missing. This study aimed to estimate the historical radiation dose before 1984 for radiation workers in Korea based on dose reconstruction models. The dose reconstruction models were derived from the nationwide self-administered questionnaire survey and the personal badge doses for workers in the cohort of the Korean Radiation Worker Study. The mean estimated annual doses between 1984 and 2016 from the dose reconstruction model were 4.67-0.6 mSv, which closely matched the reported doses of 4.51-0.43 mSv. The mean estimated annual doses between 1961 and 1983 based on the exposure scenarios developed by factors associated with radiation doses ranged from 11.08 to 4.82 mSv. The mean estimated annual doses of individuals in the cohort from 1961 to 1983 ranged from 11.15 to 4.88 mSv. Although caution needs to be exercised in the interpretation of these estimations due to uncertainty owed to the nature of extrapolation beyond the range of observed data, this study offers a sense of the radiation doses for workers during Korea's early period of radiation-related activities, which can be a useful piece of information for radiation-induced health risk assessments.

Is the Linear No-Threshold Dose-Response Paradigm Still Necessary for the Assessment of Health Effects of Low Dose Radiation?

Inevitable human exposure to ionizing radiation from man-made sources has been increased with the proceeding of human civilization and consequently public concerns focus on the possible risk to human health. Moreover, Fukushima nuclear power plant accidents after the 2011 East-Japan earthquake and tsunami has brought the great fear and anxiety for the exposure of radiation at low levels, even much lower levels similar to natural background. Health effects of low dose radiation less than 100 mSv have been debated whether they are beneficial or detrimental because sample sizes were not large enough to allow epidemiological detection of excess effects and there was lack of consistency among the available experimental data. We have reviewed an extensive literature on the low dose radiation effects in both radiation biology and epidemiology, and highlighted some of the controversies therein. This article could provide a reasonable view of utilizing radiation for human life and responding to the public questions about radiation risk. In addition, it suggests the necessity of integrated studies of radiobiology and epidemiology at the national level in order to collect more systematic and profound information about health effects of low dose radiation.

Characteristics and Trends of Occupational Radiation Doses among Korean Radiation Workers (1984-2020).

ABSTRACT: This study identified characteristics of occupational radiation doses among Korean radiation workers from 1984-2020 using the National Dose Registry. The overall mean effective dose from 1984-2020 was 1.05 mSv y -1 , with the highest mean effective dose of 2.61 mSv y -1 for non-destructive testing workers. The mean effective dose gradually decreased from 2.97 mSv in 1984 to 0.34 mSv in 2020. The largest decline ratio between 1984 and 2020 was observed in educational institutions at 97.4% (0.84 mSv in 1984 and 0.02 mSv in 2020), followed by industries at 96.5% (2.55 mSv in 1984 and 0.09 mSv in 2020). Compared to 1984, the individual dose-distribution and collective dose-distribution ratios in 2020 decreased by 82.6-99% and 53.7-94.7%, respectively. This downward trend was consistent in all occupations, while decline characteristics were different depending on occupation types, work experience, and changes in radiation safety regulations. Considering that some changes in radiation doses in the registry could be solely based on changing the recording mode regardless of the actual changes in radiation doses, a careful understanding of radiation doses in the registry is particularly relevant for future epidemiological studies.

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.

Reliability and Validity of a Nationwide Survey (the Korean Radiation Workers Study).

BACKGROUND: This study aimed to evaluate the reliability and validity of the self-administered questionnaire for Korean radiation workers. METHODS: From May 24, 2016, to June 30, 2017, 20,608 participants completed the questionnaire, providing information on sociodemographics, lifestyle, work history and practices, medical radiation exposure, and medical history, which was linked to the National Dose Registry and the National Cancer Registry. The validity of the questionnaire was evaluated using the responses of 20,608 workers, and reliability was evaluated using the responses of 3043 workers who responded to the survey twice. RESULTS: Responses concerning demographic characteristics and lifestyle showed reliability with a moderate-to-high agreement (kappa: 0.43-0.99), whereas responses concerning occupation and medical radiation exposure had a wide range of agreement (kappa: 0.05-0.95), possibly owing to temporal variability during employment. Regarding validity, responses to the question about the first year of employment had an excellent agreement with the national registry (intraclass correlation coefficient = 0.9); however, responses on cancer history had a wide range of agreement (kappa: 0.22-0.85). CONCLUSION: Although the reliability and validity of the questionnaire were not distinguished by demographic characteristics, they tended to be low among participants whose occupational radiation exposure was minimal. Overall, the information collected can be reliable for epidemiological studies; however, caution must be exercised when using information such as medical exposure and work practices, which are prone to temporal variability.

A Cohort Study of Korean Radiation Workers: Baseline Characteristics of Participants.

The Korean Radiation Worker Study investigated the health effects of protracted low-dose radiation among nuclear-related occupations in the Nuclear Safety and Security Commission in Korea. From 2016-2017, 20,608 workers were enrolled (86.5% men and 30.7% nuclear power plant workers). The mean cumulative dose ± standard deviation between 1984 and 2017 (1st quarter) was 11.8 ± 28.8 (range 0-417) mSv. Doses below recording level (≤0.1 mSv) were reported in 7901 (38.3%) cases; 431 (2%) had cumulative doses ≥100 mSv. From 1999-2016, 212 cancers (189 men, 23 women) occurred; thyroid cancer predominated (39.2%, 72 men, 11 women). In men, the standardized incidence ratio (SIR) for all cancers was significantly decreased (SIR = 0.76, 95% CI 0.66-0.88); however, that for thyroid cancer was significantly increased (SIR = 1.94, 95% CI 1.54-2.44). Compared to the non-exposed group (≤0.1 mSv), the relative risk (RR) in the exposed group (>0.1 mSv) after adjusting for sex, attained age, smoking status, and duration of employment was 0.82 (95% CI 0.60-1.12) for all cancers and 0.83 (95% CI 0.49-1.83) for thyroid cancer. The preliminary findings from this baseline study with a shorter follow-up than the latency period for solid cancer cannot exclude possible associations between radiation doses and cancer risk.

Radiation exposure and fluoroscopically-guided interventional procedures among orthopedic surgeons in South Korea.

BACKGROUND: The use of fluoroscopically-guided interventional (FGI) procedures by orthopedic surgeons has been increasing. This study aimed to investigate the occupational radiation exposure among orthopedic surgeons in South Korea. METHODS: A nationwide survey of orthopedic surgeons was conducted in South Korea in October 2017. The dosimetry data of the participants were obtained from the National Dosimetry Registry. The orthopedic surgeons were categorized by job specialty [spine or trauma specialists, other orthopedic specialists, and residents], and descriptive statistics for the demographics and work-related characteristics were presented. Multivariable logistic regression analysis was used to evaluate the risk factors for the orthopedic surgeons who were not linked with the dosimetry data. RESULTS: Among the total participants (n = 513), 40.5% of the orthopedic surgeons spent more than 50% of their time working with the FGI procedures when compared with their overall work. The average frequency of the FGI procedures among the orthopedic surgeons was 12.3 days per month. Less than 30% of the participants were regularly provided with radiation monitoring badges. The proportion of subjects who always wore lead aprons and thyroid shields were 52 and 29%, respectively. The residents group experienced more unfavorable working conditions of radiation exposure than the other specialists. The dosimetry data were not significantly linked among the residents (odds ratio [OR] 2.10, 95% confidence interval [CI] 1.11-3.95) and orthopedic surgeons working at small hospitals (OR 4.76, 95% CI 1.05-21.51). CONCLUSIONS: Although orthopedic surgeons often performed FGI procedures, they wore protective gear less frequently, and a large proportion of orthopedic surgeons were not monitored by the national radiation dosimetry system. As the number of radiation procedures performed by the orthopedic surgeons increases, more intensive approaches are needed to reduce radiation exposure, especially for spine and trauma surgeons.

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.

Radiation-related occupational cancer and its recognition criteria in South Korea.

Ionizing radiation is a well-known carcinogen, and is listed as one carcinogenic agent of occupational cancer. Given the increase in the number of workers exposed to radiation, as well as the increase in concern regarding occupational cancer, the number of radiation-related occupational cancer claims is expected to increase. Unlike exposure assessment of other carcinogenic agents in the workplace, such as asbestos and benzene, radiation exposure is usually assessed on an individual basis with personal dosimeters, which makes it feasible to assess whether a worker's cancer occurrence is associated with their individual exposure. However, given the absence of a threshold dose for cancer initiation, it remains difficult to identify radiation exposure as the root cause of occupational cancer. Moreover, the association between cancer and radiation exposure in the workplace has not been clearly established due to a lack of scientific evidence. Therefore, criteria for the recognition of radiation-related occupational cancer should be carefully reviewed and updated with new scientific evidence and social consensus. The current criteria in Korea are valid in terms of eligible radiogenic cancer sites, adequate latent period, assessment of radiation exposure, and probability of causation. However, reducing uncertainty with respect to the determination of causation between exposure and cancer and developing more specific criteria that considers mixed exposure to radiation and other carcinogenic agents remains an important open question.

The Significance of TROP2 Expression in Predicting BRAF Mutations in Papillary Thyroid Carcinoma.

BACKGROUND: Trophoblast antigen 2 (TROP2) is a human trophoblast cell-surface glycoprotein that is overexpressed in several types of epithelial cancers, and is suggested to be associated with an unfavorable prognosis. BRAF mutations are the most common genetic alteration in papillary thyroid carcinoma (PTC). We evaluated the correlation between TROP2 expression and BRAF mutation in PTC. METHODS: First, we carried out pyrosequencing for BRAF mutations and immunohistochemistry for TROP2 expression with a tissue microarray consisting of 52 PTC cases. Membranous staining in at least 5% of tumor cells was designated as positive staining and we analyzed the relationship between TROP2 expression and diverse clinicopathological factors, including BRAF mutation. Second, we tested TROP2 mRNA expression in three thyroid cancer cell lines with BRAF mutations (BCPAP, SNU790, and 8505C) and a normal thyroid cell line. Additionally, we checked TROP2 protein levels in a normal thyroid cell line after introduction of the BRAF V600E mutation. RESULTS: In this study, 21 of 26 cases with BRAF mutation showed TROP2 immunoreactivity, whereas all 26 cases without BRAF mutation showed no immunoreactivity for TROP2 with a statistically significant difference (p<.001). Upregulation of TROP2 mRNA was observed in all three thyroid cancer cell lines, but not in the normal thyroid cell line. Interestingly, however, the TROP2 expression was increased in the normal thyroid cell line after introduction of the BRAF V600E mutation. CONCLUSIONS: Based on these results, we concluded that TROP2 expression is significantly associated with BRAF mutation and that TROP2 immunohistochemistry could be used for predicting BRAF mutations or diagnosing papillary thyroid carcinoma.

Perception of low dose radiation risks among radiation researchers in Korea.

Expert's risk evaluation of radiation exposure strongly influences the public's risk perception. Experts can inform laypersons of significant radiation information including health knowledge based on experimental data. However, some experts' radiation risk perception is often based on non-conclusive scientific evidence (i.e., radiation levels below 100 millisievert), which is currently under debate. Examining perception levels among experts is important for communication with the public since these individual's opinions have often exacerbated the public's confusion. We conducted a survey of Korean radiation researchers to investigate their perceptions of the risks associated with radiation exposure below 100 millisievert. A linear regression analysis revealed that having ≥ 11 years' research experience was a critical factor associated with radiation risk perception, which was inversely correlated with each other. Increased opportunities to understand radiation effects at < 100 millisievert could alter the public's risk perception of radiation exposure. In addition, radiation researchers conceived that more scientific evidence reducing the uncertainty for radiation effects < 100 millisievert is necessary for successful public communication. We concluded that sustained education addressing scientific findings is a critical attribute that will affect the risk perception of radiation exposure.

Factors associated with the risk perception and purchase decisions of Fukushima-related food in South Korea.

Following the Fukushima nuclear power plant accident, the risk level perceived by Koreans on the radioactive contamination of Japanese food that is being distributed in Korea remains high. Many of these perceptions are based on subjective risk perception rather than an objective measure with scientific evidence, which makes communicating risks more difficult; therefore, it is critical to understand factors associated with risk perception for effective risk communication. In this study, we identified variables that are associated with buying tendencies and opinions about the regulatory policy of Japanese seafood after the accident. A survey was conducted with 1045 adults aged over 20 years in Korea. The majority (68.8%) responded that they would not purchase Japanese seafood when radioactivity levels in the food were non-detectable. Moreover, 82.2% responded that the current levels of import restrictions on Japanese seafood must be maintained. Despite many concerns regarding the exposure to radiation and the effects from food products following the Fukushima accident, the opportunities to encounter and to collect correct information remain limited and average radioactive knowledge scores were low (3.63 out of 9). Of the various characteristics associated with purchase decisions and agreement on the current import restraints of Japanese seafood, trust levels in the government and the mass media for providing information on radioactivity were major factors that influenced risk perception. While the scope of this study was limited to seafood, it is very closely tied to daily lives, where we revealed differences about risk perceptions and agreement on import restraints of Japanese seafood per a complex mixture of individual characteristics and the surrounding environment. These results provide useful information to understand the risk perception of the potential radioactive contamination of food and to predict the public's responses to food consumption and import restraint policies due to nuclear accidents in neighboring countries.