Lifetime cancer risks from occupational radiation exposure among workers at interventional radiology departments.

PURPOSE: Interventional medical radiation workers represent an under-studied population worldwide, although they receive relatively high occupational radiation doses. This study aimed to estimate the lifetime cancer risk from occupational radiation exposure among workers at interventional radiology departments. METHODS: A field survey of interventional medical workers in nationwide branches of the Korean Society of Interventional Radiology was conducted in 2017. Organ-specific radiation doses were estimated using national dose registry data and conversion coefficients provided by the International Commission on Radiological Protection. Lifetime attributable risk (LAR) and lifetime fractional risk (LFR) were calculated based on realistic exposure scenarios using a radiation risk assessment tool. RESULTS: LARs from occupational radiation exposure until the age of retirement for all cancers combined were 338 (90.3-796.1), 121 (33.5-288.7), and 156 (41.1-390.6) per 100,000 individuals for male radiologists, male radiologic technologists, and female nurses, respectively. LFR for all cancers combined ranged from 0.22% (0.06-0.53) to 0.63% (0.17-1.47). Regarding the organ site, the highest LAR and LFR among all groups were observed for thyroid cancer. CONCLUSION: This study provides timely evidence of potential cancer burden from the current levels of occupational radiation exposure among workers at interventional radiology departments. The risks varied by occupational groups, and workers, particularly interventional radiologists, need to be carefully monitored for radiation.

Occupational radiation exposure and morbidity of circulatory disease among diagnostic medical radiation workers in South Korea.

OBJECTIVES: We investigated the association between low-dose external occupational radiation exposure and circulatory disease morbidity among diagnostic medical radiation workers. METHODS: A cohort of 11 500 diagnostic medical radiation workers was linked with the National Dosimetry Registry data and the National Health Insurance Service data. Relative risks (RRs) were calculated to explore the association between occupational factors and circulatory disease morbidity, and excess relative risks per 100 milligray (ERR/100 mGy) were estimated to quantify the radiation dose-response relationship. RESULTS: Overall, there were 2270 cases of circulatory diseases during 93 696 person-years of observation (average follow-up=8.1 years). RRs for hypertension were significantly increased for individuals who started working before 2000 compared with those who started in 2005 and later. ERR/100 mGy for all circulatory diseases was 0.14 (95% CI -0.57 to 0.99). Radiation risks of cerebrovascular diseases and ischaemic heart disease were non-significantly increased with estimates of individual cumulative doses to the heart (ERR/100 mGy=3.10 (-0.75 to 11.59) and 1.22 (-0.71 to 4.73), respectively). However, ERR estimates were generally more strongly positive for female versus male workers and for younger workers versus more than 50-year-old workers. CONCLUSIONS: This study provides little evidence in support of a positive association between occupational radiation exposure and the overall risk of circulatory disease over a short follow-up period among medical radiation workers in South Korea. However, significantly increased RR with earlier year first worked, elevated ERR in female workers and young workers should be further followed up.

Suicide deaths among diagnostic medical radiation workers in South Korea, 1996-2017.

OBJECTIVES: Suicide is a leading cause of death in the working-age population. We investigated suicide mortality among diagnostic medical radiation workers in relation to their demographic and occupational factors in South Korea. METHODS: The study population consisted of all diagnostic medical radiation workers enrolled in the National Dosimetry Registry from 1996 to 2011. The registry data were linked with mortality data through the end of 2017. We calculated age-standardised suicide rates, standardised mortality ratios (SMRs) and rate ratios (RRs) by demographic and occupational factors. RESULTS: A total of 207 suicides were identified among 94 367 medical radiation workers, exhibiting a suicide rate of 14.0 per 100 000 person-years. Compared with the general population, suicide rates were lower for both male and female workers (SMR 0.49, 95% confidence interval (CI) 0.42 to 0.57; SMR 0.54, 95% CI 0.41 to 0.70, respectively). Similarly, decreased SMRs were observed across job titles and other work-related factors. However, a shorter duration of employment was positively associated with RRs for suicide; risks were 2.74 (95% CI 1.56 to 4.81) and 4.66 (95% CI 1.53 to 14.20) times higher in male and female workers with less than 1 year of employment, respectively, than in those with at least 10 years of employment. CONCLUSIONS: Diagnostic medical radiation workers in South Korea showed lower suicide rates than in the general population. However, a shorter duration of employment was associated with higher risk of suicide. Suicide prevention efforts could target workers engaged in short-term employment.

Quantifying the contributions of age, sex, methods, and urbanicity to the changing suicide rate trends in South Korea, 2001-2016.

PURPOSE: Suicide rates in South Korea have been one of the highest in the world. The aim of this study is to quantify the contributions of age, sex, method, and place of residence to the trends of the suicide rates between 2001 and 2016 in South Korea. METHODS: Using the suicide data obtained from the South Korean National Death Registration data set for the years 2001-2016, a Joinpoint regression analysis was conducted to determine if there was a significant change in the trend of suicide rates. Next, a decomposition analysis method was used to quantify the contributions of age, sex, method, and places of residence to the changes in the suicide rates. RESULTS: Suicide rates increased between 2001 and 2010, and decreased between 2010 and 2016. Among all the age groups, the 65-79 age group contributed most to the rise (18% in men and 7% in women) and fall (- 15% in men and - 14% in women) of suicide rates. Men contributed much more than women to the increasing trend of suicide rate (63.0% vs. 37.0%). Hanging was the key method of suicide, dominating the ups and downs of the suicide rates. The rates of suicide by pesticide poisoning have been decreasing since 2005 and suicide by charcoal burning continued to increase against a decreasing trend of suicide rate during the period of 2010-2016. The gap of the metropolitan-city-rural suicide rates was narrowing during the period under study, although the rural areas remained to have the highest suicide rates. CONCLUSION: The ups and downs of suicide rates in South Korea were not uniform across different sociodemographic groups. Age, sex, method, and place of residence contributed differently to the changes in suicide rates. Suicide prevention measures can be more focused on certain age-sex-method-region subgroups.

Thyroid cancer risks among medical radiation workers in South Korea, 1996-2015.

BACKGROUND: Thyroid cancer rates, especially among children, are known to be increased by radiation exposure. However, little is known about the impact of chronic low-dose radiation exposure on thyroid cancer risk in adulthood. This study examined radiation effects on thyroid cancer rates as well as an overall evaluation of thyroid cancer risk among medical radiation workers. METHODS: Data on all diagnostic medical radiation workers enrolled in the national dosimetry registry between 1996 and 2011 were linked with the cancer registry data through 2015. Standardized incidence ratios (SIRs) were used to compare the observed cancer incidence rates in this population to those for the general population while internal comparisons were used to estimate relative risks (RRs) for occupational history and excess relative risks (ERRs) were used to quantify the radiation dose-response relationship. RESULTS: Overall, 827 thyroid cancer cases were reported among 93,922 medical radiation workers. Thyroid cancer SIRs were significantly higher than expected for both men (SIR 1.72, 95% confidence interval [CI] 1.53 to 1.91) and women (SIR 1.18, 95% CI 1.08 to 1.28). However, RRs for thyroid cancer by job title and duration of employment showed no particular pattern among diagnostic medical radiation workers. There were no indications of a significant dose effect on thyroid cancer rates for either men (ERR/100 mGy 0.07, 95% CI -0.38 to 0.53) or women (ERR/100 mGy -0.13, 95% CI -0.49 to 0.23). The findings were similar for different job titles or when limited to workers employed for at least one year. CONCLUSIONS: While thyroid cancer incidence rates among Korean medical radiation workers were somewhat higher than those in the general population, there was no significant evidence that this increase was associated with occupational radiation dose. Additional follow-up together with consideration of other risk factors should provide useful information on thyroid cancer rates in this cohort.

Projected lifetime cancer risks from occupational radiation exposure among diagnostic medical radiation workers in South Korea.

BACKGROUND: Timely assessment of cancer risk from current radiation exposure among medical radiation workers can contribute to the development of strategies to prevent excessive occupational radiation exposure. The purpose of the present study is to estimate the lifetime risk of cancers induced by occupational radiation exposure among medical radiation workers. METHODS: Using estimated organ doses and the RadRAT risk assessment tool, the lifetime cancer risk was estimated among medical radiation workers who were enrolled in the Korean National Dose Registry from 1996 to 2011. Median doses were used for estimating the risk because of the skewed distribution of radiation doses. Realistic representative exposure scenarios in the study population based on sex, job start year, and occupational group were created for calculating the lifetime attributable risk (LAR) and lifetime fractional risk (LFR). RESULTS: The mean estimated lifetime cancer risk from occupational radiation exposure varied significantly by sex and occupational group. The highest LAR was observed in male and female radiologic technologists who started work in 1991 (264.4/100,000 and 391.2/100,000, respectively). Female workers had a higher risk of radiation-related excess cancer, although they were exposed to lower radiation doses than male workers. The higher LAR among women was attributable primarily to excess breast and thyroid cancer risks. LARs among men were higher than women in most other cancer sites. With respect to organ sites, LAR of colon cancer (44.3/100,000) was the highest in male radiologic technologists, whereas LAR of thyroid cancer (222.0/100,000) was the highest in female radiologic technologists among workers who started radiologic practice in 1991. Thyroid and bladder cancers had the highest LFR among radiologic technologists. CONCLUSIONS: Our findings provide an assessment of the potential cancer risk from occupational radiation exposure among medical radiation workers, based on current knowledge about radiation risk. Although the radiation-related risk was small in most cases, it varied widely by sex and occupational group, and the risk would be underestimated due to the use of median, rather than mean, doses. Therefore, careful monitoring is necessary to optimize radiation doses and protect medical radiation workers from potential health risks, particularly female radiologic technologists.

Mortality among diagnostic medical radiation workers in South Korea, 1996-2015.

OBJECTIVES: To evaluate the risk for all-cause and cause-specific mortality in diagnostic medical radiation workers in South Korea. METHODS: The study population included all diagnostic medical radiation workers enrolled in the National Dosimetry Registry (NDR) between 1996 and 2011. NDR data were linked with mortality data obtained from national registries through 2015. Standardised mortality ratios (SMRs) and relative standardised mortality ratios (rSMRs) were calculated for external comparison and for adjustment of the cohort's overall healthiness. RESULTS: A total of 1099 deaths (974 in men and 125 in women) were reported from among 80 837 medical radiation workers. The SMRs for all causes of death were significantly lower than expected in both men (SMR 0.45, 95% CI 0.42 to 0.48) and women (SMR 0.49, 95% CI 0.41 to 0.58). No excesses were observed for any specific cause of death. The findings were similar by job title, calendar year of entry and year of birth. However, relative to all causes of death, mortality from all cancers (rSMR 1.60, 95% CI 1.41 to 1.82), leukaemia, colon cancer, stomach cancer and diseases of the circulatory system increased significantly among male workers. The results for female workers were limited due to small number of deaths; however, the rSMR for all cancers was significantly elevated (rSMR 1.70, 95% CI 1.17 to 2.46). CONCLUSIONS: This cohort showed lower mortality among diagnostic medical radiation workers than in the general population. However, occupational factors may have been involved in the increased relative mortality for several causes of death.

The Burden of Acute Pesticide Poisoning and Pesticide Regulation in Korea.

BACKGROUND: This study aimed to estimate the burden of acute pesticide poisoning and to determine its trend with recently implemented pesticide regulations. METHODS: Disability-adjusted life-years (DALYs) were calculated as the sum of years of life lost (YLLs) and years lived with disability (YLDs) due to acute pesticide poisoning using the methods of the Global Burden of Disease Study 2013. The values of YLLs, YLDs, and DALYs were stratified by sex, age groups, intentionality of poisoning, and causative agents. RESULTS: From 2006 to 2014, DALYs decreased by 69% (from 69,550 to 21,742). The decreasing tendency of DALYs was especially marked from 2011. The total burden of acute pesticide poisoning was mainly caused by YLLs and intentional pesticide poisoning. The highest DALYs due to acute pesticide poisoning occurred in those in their 40s and 50s; however, the decreased rates of DALYs were higher in those aged 10-49 years than in those aged more than 50 years. Herbicides including paraquat contributed to the largest proportion of total DALYs. CONCLUSION: As this is the first study to quantify the burden of acute pesticide poisoning using DALYs, our results provide comprehensive evidence of the importance of using strict regulations to prevent public health hazards due to acute pesticide poisoning.

Reliability of self-reported questionnaire on occupational radiation practices among diagnostic radiologic technologists.

BACKGROUND: We aimed to assess the reliability of a self-reported questionnaire on occupational radiation practices among radiologic technologists. METHODS: We enrolled 941 participants who had repeatedly completed the questionnaire from the 2012-2013 radiologic technologists' health study in South Korea. We used percentage agreement, kappa statistics, and intraclass correlation coefficient (ICC) to assess the reliability of responses on work practices. RESULTS: Overall agreement for ever-never diagnostic radiation procedures was high (87.5-97.5%), and κ values indicated substantial agreement (0.66-0.86) in all procedures except cephalometric and intraoral radiography. For the information of year of work start and working duration, high agreement was obtained (ICC: 0.99 and 0.98, respectively). However, use of a worn dosimeter and of personal protective equipment showed only moderate to substantial agreement. CONCLUSIONS: Self-reported information on working practices regarding radiation exposure in radiologic technologists was reliable enough for epidemiologic studies. Am. J. Ind. Med. 60:377-385, 2017. © 2017 Wiley Periodicals, Inc.

Potential underestimation of pesticide suicide and its impact on secular trends in South Korea, 1991-2012.

BACKGROUND: Pesticide ingestion is among the most commonly used suicide methods globally. Underestimation of deaths by pesticide self-poisoning is thought to be common but under-researched. We investigated potential misclassification and underestimation of suicide by pesticide poisoning and their impact on trends in pesticide suicide in South Korea. METHODS: We compared sociodemographic profiles between deaths certified as suicide, undetermined deaths and injuries by poisoning using pesticides, unspecified chemicals and medicines/alcohol in South Korea (1991-2012), and calculated similarity scores. Joinpoint regression analysis was used to examine time trends. RESULTS: The profiles of deaths classified as pesticide suicides showed generally similar patterns to those for undetermined deaths/injuries by poisoning using pesticides and suicides/undetermined deaths/injuries by poisoning using unspecified chemicals. Over the study period, the number of pesticide suicides (on average 2033 per year; range 623-3530) would increase by 15%, 23% and 31%, when assuming that 20%, 30% and 40% of deaths in alternative cause-of-death categories were misclassified pesticide suicides respectively. Age-standardised rates of pesticide suicide increased more than four times in 1991-2003 but fell by around 50% in 2003-2012. This trend did not change when the assumed proportion of misclassification was 20%, whereas the rapid increase in 2000-2003 would be lessened if misclassification occurred by 30% or more. CONCLUSIONS: Pesticide suicides may be underestimated in South Korea as some are possibly misclassified as deaths due to other causes; however, such underestimation would not substantially affect estimated secular trends.

The radiologic technologists' health study in South Korea: study design and baseline results.

PURPOSE: To describe the study design, methods, and baseline results of a prospective cohort of radiologic technologists which we have initiated in South Korea. METHODS: The cohort participants were enrolled through a self-administered questionnaire survey administered from April 2012 to May 2013. Survey data were linked with radiation dosimetry, a cancer registry, and health insurance data by personal identification numbers. A nationwide representative survey was also conducted using a stratified random sampling design with face-to-face interviews. RESULTS: A total of 12,387 radiologic technologists were enrolled, which accounted for approximately 63% of all diagnostic radiologic technologists working in South Korea. For nationwide survey, 585 workers were interviewed using the detailed questionnaire, and buccal cells were also collected by scraping the inside of the cheek. The majority of study subjects were under 50-year-old and male workers. The average annual effective dose of radiation declined both men (from 2.75 to 1.43 mSv) and women (from 1.34 to 0.95 mSv) over the period of 1996-2011. A total of 99 cancers (66 cancers in men and 33 in women) were reported from 1992 to 2010. The standardized incidence ratio of all cancer combined was significantly lower in men (SIR = 0.75, 95% CI 0.58-0.96) than general population, but the ratios for thyroid cancer were significantly higher than expected among both men and women. CONCLUSIONS: This cohort provides comprehensive information on work activities and health status of diagnostic radiologic technologists. In addition, the nationwide representative sample provides unique opportunities compared with previous radiologic technologist studies.

Attributable fraction of tobacco smoking on cancer using population-based nationwide cancer incidence and mortality data in Korea.

BACKGROUND: Smoking is by far the most important cause of cancer that can be modified at the individual level. Cancer incidence and mortality rates in Korea are the highest among all Asian countries, and smoking prevalence in Korean men is one of the highest in developed countries. The purpose of the current study was to perform a systematic review and provide an evidence-based assessment of the burden of tobacco smoking-related cancers in the Korean population. METHODS: Sex- and cancer-specific population-attributable fractions (PAF) were estimated using the prevalence of ever-smoking and second-hand smoking in 1989 among Korean adults, respectively, and the relative risks were estimated from the meta-analysis of studies performed in the Korean population for ever-smoking and in the Asian population for passive smoking. National cancer incidence data from the Korea Central Cancer Registry and national cancer mortality data from Statistics Korea for the year 2009 were used to estimate the cancer cases and deaths attributable to tobacco smoking. RESULTS: Tobacco smoking was responsible for 20,239 (20.9%) cancer incident cases and 14,377 (32.9%) cancer deaths among adult men and 1,930 (2.1%) cancer incident cases and 1,351 (5.2%) cancer deaths among adult women in 2009 in Korea. In men, 71% of lung cancer deaths, 55%-72% of upper aerodigestive tract (oral cavity, pharynx, esophagus and larynx) cancer deaths, 23% of liver, 32% of stomach, 27% of pancreas, 7% of kidney and 45% of bladder cancer deaths were attributable to tobacco smoking. In women the proportion of ever-smoking-attributable lung cancer was 8.1%, while that attributable to second-hand smoking among non-smoking women was 20.5%. CONCLUSIONS: Approximately one in three cancer deaths would be potentially preventable through appropriate control of tobacco smoking in Korean men at the population level and individual level. For Korean women, more lung cancer cases and deaths were attributable to second-hand than ever-smoking. Effective control programs against tobacco smoking should be further developed and implemented in Korea to reduce the smoking-related cancer burden.

Amyotrophic lateral sclerosis and agricultural environments: a systematic review.

The aim of this study was to examine the relationship between the risk of amyotrophic lateral sclerosis (ALS) and exposure to rural environments. Studies were identified through OVID MEDLINE and EMBASE search up to September 2013 using as keywords rural residence, farmers, and pesticide exposure. Twenty-two studies were included for this meta-analysis. Summary odds ratios (ORs) were calculated using random effect model by type of exposure index, and subgroup analyses were conducted according to study design, gender, region, case ascertainment, and exposure assessment. The risk of ALS was significantly increased with pesticide exposure (OR, 1.44; 95% CI, 1.22-1.70) and with farmers (OR, 1.42; 95% CI, 1.17-1.73), but was not significant with rural residence (OR, 1.25; 95% CI, 0.84-1.87). The risk estimates for subgroup analysis between pesticide exposure and ALS indicated a significant positive association with men (OR, 1.96), and in studies using El Escorial criteria for ALS definition (OR, 1.63) and expert judgment for pesticide exposure (OR, 2.04) as well. No significant publication bias was observed. Our findings support the association of pesticide exposure and an increased risk for ALS, stressing that the use of more specific exposure information resulted in more significant associations.

Acute pesticide poisoning among children in South Korea: findings from National Health Insurance claims data, 2006-2009.

OBJECTIVES: The aim of this study was to estimate the incidence of acute pesticide poisoning among children in South Korea and describe the related epidemiologic characteristics. METHODS: We evaluated the age-standardized rates of incidence of pesticide poisoning among children in South Korea from 2006 through 2009 using National Health Insurance claims data. RESULTS: A total of 1232 children aged 0-14 years were identified from the acute pesticide poisoning cases reported across South Korea during the study period. The annual average age-standardized rate of incidence from acute pesticide poisoning was 3.6 per 100 000. The majority of the cases were identified in the categories of the 1-4-year-old age-group (56.5%), outpatients (80.0%), single-day visit to a hospital (70.4%) and summer occurrence (43.3%). CONCLUSIONS: Acute pesticide poisoning is prevalent among children in South Korea; therefore, intervention efforts are needed to reduce the cases of pesticide poisoning among children.

Paraquat application and respiratory health effects among South Korean farmers.

OBJECTIVES: Paraquat is commonly used worldwide as major herbicide. The objective of this study was to investigate the association among farmers between occupational paraquat exposure and respiratory health effects. METHODS: A cross-sectional survey of health effects related to an oil spill was conducted in South Korea from 2008 to 2009. For this analysis, a total of 2882 full-time farmers were selected from the overall sample. Data collection included an interviewer-administered questionnaire and spirometry testing. Logistic regression analysis and linear regression analysis were performed to evaluate the relationship between paraquat exposure and respiratory health outcomes after adjustment for potential confounders. RESULTS: The risks of self-reported physician-diagnosed asthma, chronic obstructive pulmonary disease and allergic rhinitis were non-significantly increased among paraquat-applying farmers compared with non-paraquat-applying farmers. Although the results of a pulmonary function test fell within normal limits, a decline in forced vital capacity and forced expiratory volume in one second was apparent among paraquat-applying farmers compared with non-paraquat-applying farmers. Forced vital capacity (ß = -5.20, p<0.001) and forced expiratory volume in one second (ß = -1.89, p = 0.010) significantly decreased with each unit increase in years of paraquat application. Paraquat-applying farmers showed a significant exposure-response relationship between restrictive ventilatory defects and paraquat application years (p trend = 0.015) or lifetime days of application (p trend = 0.007). CONCLUSIONS: Our findings suggest a possible association between paraquat application and adverse respiratory health effects among farmers.

Incidence of acute occupational pesticide poisoning among male farmers in South Korea.

BACKGROUND: Pesticide poisoning from agricultural labor has been recognized as a major public health problem among farmers worldwide. The objective of this study was to examine the incidence of acute occupational pesticide poisoning among male farmers in South Korea. METHODS: A nationwide sampling survey of male farmers was conducted in South Korea. This survey used a stratified multistage probability sampling design and adopted the face-to-face interview method. A total of 1,958 male farmers were interviewed in order to estimate the incidence of acute occupational pesticide poisoning in rural areas in 2010. Based on a self-reported definition, the incidence rate in 2010 and the lifetime hospitalization rate due to acute occupational pesticide poisoning among male farmers were estimated. RESULTS: The incidence rate of acute occupational pesticide poisoning was 24.7 (95% CI 22.1-27.2) per 100 male farmers, which corresponds to 209,512 cases across South Korea in 2010. About 12% of the pesticide poisoning cases included either visiting a medical doctor or hospitalization. The lifetime rate of hospitalization due to occupational pesticide poisoning was 6.1 (95% CI 4.9-7.3) among male farmers. Poisoning occurred mainly when farmers were applying pesticides during summer. CONCLUSION: Our nationwide sampling survey demonstrated that acute occupational pesticide poisonings are highly prevalent among male South Korean farmers. Intensive intervention efforts to reduce occupational pesticide poisoning are urgently needed in South Korea.

Data integration of National Dose Registry and survey data using multivariate imputation by chained equations.

INTRODUCTION: Data integration is the process of merging information from multiple datasets generated from different sources, which can obtain more information in comparison to to one data source. All diagnostic medical radiation workers were enrolled in National Dose Registry (NDR) from 1996 to 2011, linked with mortality and cancer registry data. (https://kdca.go.kr/) Survey was conducted during 2012-2013 using self-reported questionnaire on occupational radiation practices among diagnostic medical radiation workers. METHODS: Data integration of NDR and Survey was performed using the multivariate imputation by chained equations (MICE) algorithm. RESULTS: The results were compared by sex and type of job because characteristics of target variables for imputation depend on these variables. There was a difference between the observed and pooled mean for the frequency of interventional therapy for nurses due to different type of medical facility distribution between observed and completed data. Concerning the marital status of males and females, and status of pregnancy for females, there was a difference between observed and pooled mean because the distribution of the year of birth was different between the observed and completed data. For lifetime status of smoking, the percentage of smoking experience was higher in the completed data than in the observed data, which could be due to reasons, such as underreporting among females and the distribution difference in the frequency of drinking between the observed and completed data for males. CONCLUSION: Data integration can allow us to obtain survey information of NDR units without additional surveys, saving us time and costs for the survey.

Correction: Data integration of National Dose Registry and survey data using multivariate imputation by chained equations.

[This corrects the article DOI: 10.1371/journal.pone.0261534.].

Childhood cancer mortality and birth characteristics in Korea: a national population-based birth cohort study.

To examine the relationship between birth characteristics and childhood cancer mortality, a retrospective cohort study of Korean children was conducted using data collected by the national birth register between 1995 and 2006, which were then individually linked to death data. A cohort of 6,479,406 children was followed from birth until their death or until December 31, 2006. Poisson regression analyses were used to calculate rate ratios of childhood cancer deaths according to birth characteristics. A total of 1,469 cancer deaths were noted and the childhood cancer mortality rate was found to be 3.43 per 100,000 person-years in Korea during the period of 1995-2006. The birth characteristics examined in this study (i.e. , birth weight, gestational age, multiple births, parental ages, and number of siblings) were generally found to be not significantly associated with childhood cancer mortality, and the associations did not vary meaningfully with gender nor with cancer sites. However, among children aged 5-11 yr, higher birth weight was associated with elevated childhood cancer mortality (rate ratio = 1.28, 95% confidence interval 1.04-1.58). Our results offer no overall associations between childhood cancer mortality and birth characteristics, but suggest that the association may be specific to age group.

Increased Incidence of Thyroid Cancer in Occupational Radiation Epidemiology: Attribution to Screening among Radiation Workers.

In most studies on radiation workers, the incidence of thyroid cancer was determined to be higher than among the general population; this is generally assumed to be due to overdiagnosis through thyroid screening. However, there is a lack of evidence on the association between thyroid screening and increased thyroid cancer incidence in most occupational studies. In this study, we compared thyroid cancer screening rates between the general population and radiation workers with various occupations and examined the relationship between these rates and thyroid cancer incidence. We compared thyroid screening rates between radiation workers and the general population with age- and sex-standardized screening ratios (SSRs) using data from two national surveys conducted during 2015-2017 in Korea, and assessed the correlation between these ratios and age- and sex-standardized incidence ratios (SIRs) for thyroid cancer. Screening rates were higher among radiation workers than among the general population, with an overall SSR of 1.58 (95% confidence interval: 1.54-1.62). When various types of occupations were compared, those with an increased SSR also had an increased SIR. SSRs remained high even when the screening period was restricted to the year preceding the survey (the year after the establishment of guidelines for thyroid cancer screening aimed at reducing overdiagnosis). In conclusion, the increased incidence of thyroid cancer among radiation workers compared to that among the general population can be attributed mainly to increased thyroid screening rates. Additional efforts are needed to reduce unnecessary thyroid cancer screening in occupational populations, particularly in those with better access to healthcare, in terms of clinical rationale and for assessing the true increase in thyroid cancer incidence.