Probability of causation for occupational cancer after exposure to ionizing radiation

BACKGROUND: Probability of causation (PC) is a reasonable way to estimate causal relationships in radiation-related cancer. This study reviewed the international trend, usage, and critiques of the PC method. Because it has been used in Korea, it is important to check the present status and estimation of PC in radiation-related cancers in Korea. METHODS: Research articles and official reports regarding PC of radiation-related cancer and published from the 1980s onwards were reviewed, including studies used for the revision of the Korean PC program. PC has been calculated for compensation-related cases in Korea since 2005. RESULTS: The United States National Institutes of Health first estimated the PC in 1985. Among the 106 occupational diseases listed in the International Labor Organization Recommendation 194 (International Labor Office (ILO), ILO List of Occupational Diseases, 2010), PC is available only for occupational cancer after ionizing radiation exposure. The United States and United Kingdom use PC as specific criteria for decisions on the compensability of workers’ radiation-related health effects. In Korea, PC was developed firstly as Korean Radiation Risk and Assigned Share (KORRAS) in 1999. In 2015, the Occupational Safety and Health Research Institute and Radiation Health Research Institute jointly developed a more revised PC program, Occupational Safety and Health-PC (OSH-PC). Between 2005 and 2015, PC was applied in 16 claims of workers’ compensation for radiation-related cancers. In most of the cases, compensation was given when the PC was more than 50%. However, in one case, lower than 50% PC was accepted considering the possibility of underestimation of the cumulative exposure dose. CONCLUSIONS: PC is one of the most advanced tools for estimating the causation of occupational cancer. PC has been adjusted for baseline cancer incidence in Korean workers, and for uncertainties using a statistical method. Because the fundamental reason for under- or over-estimation is probably inaccurate dose reconstruction, a proper guideline is necessary.

Ionizing Radiation-induced Diseases in Korea

Radiation risk has become well known through epidemiological studies of clinically or occupationally exposed populations, animal experiments, and in vitro studies; however, the study of radiation related or induced disease has been limited in Korea. This study is to find the level of occupational radiation exposure for various kinds of accidents, compensated occupational diseases, related studies, and estimations on future occupational disease risks. Research data of related institutions were additionally investigated. About 67% of 62,553 radiation workers had no exposure or less than 1.2 mSv per year. The 5 reported cases on radiation accident patients in Korea occurred during nondestructive testing. According to the recent rapid increase in the number of workers exposed to radiation, a higher social recognition of cancer, and an increasing cancer mortality rate, it is expected that occupational disease compensation will rapidly increase as well. Therefore, it is important to develop scientific and objective decision methods, such as probability of causation and screening dose in the establishment of an exposure and health surveillance system.

Reliability of a Questionnaire in an Epidemiological Study for Nuclear Power Plants Workers in Korea / 대한산업의학회지

OBJECTIVE: This study was conducted to evaluate the reliability of a questionnaire from an epidemiological study for nuclear power plants workers in Korea. METHODS: Among a total of 8,832 nuclear power plants workers who participated in the questionnaire survey, we selected 646 workers who repeatedly submitted the self-reported questionnaire. The reliability of the questionnaire for the categorical items was measured using kappa statistics and percentages of exact agreement, false disagreement and positive disagreement. Significance was evaluated for the continuous items by paired t-tests and intra-class correlation coefficients (ICCs). RESULTS: The questionnaire was observed to be highly reliable for the smoking history (kappa=0.85), which is known as an important confounding factor in assessing the cancer risk among radiation workers. Education level as a surrogate for the socio-economic status also appeared to be highly reliable with a kappa=0.89 and 95.09% of exact agreement. The history of alcohol drinking, medical exams and diseases showed more than moderately good agreement between the first and second responses (kappa>0.4). The self-reported values for physical measurements, the smoking period and smoking amount, and the period of alcohol drinking were highly correlated between the two responses (ICC>0.7). CONCLUSIONS: The questionnaire from an epidemiological study for nuclear power plants workers in Korea was found to be reliable for most items. To estimate the cancer or noncancer risk for nuclear power plants workers, we need to use the national database for incidence of diseases or death from diseases and the exposure history, and the medical records as well as the data collected from this study.

Use of Screening Dose to Evaluate the Work-relatedness of Cancers Occurring among Korean Radiation Workers / 대한산업의학회지

OBJECTIVES: To propose a screening dose based on the probability of causation (PC) to simplify the evaluation procedure for the work-relatedness of the cancers occurring among Korean radiation workers. METHODS: Under the PC uncertainty distribution, the screening dose was defined in which the maximum PC is equivalent to 50% for single exposure to radiation, after which the values were calculated according to three significance levels: 90%, 95%, and 99%. By using the screening doses for each cancer, we also predicted the number of compensations for the occupational cancers among the current Korean radiation workers to determine a reasonable criterion for the significance level. RESULTS: If the cumulative dose received by a radiation worker with cancer is less than the screening dose, then PC can not be greater than 50%, i.e., the case can not be awarded as an occupational disease. The numbers of compensation cases for a future decade were predicted to be 3-5, 4-6, and 6-10 at the significance levels of 90%, 95%, and 99%, respectively. CONCLUSIONS: The procedure to evaluate the occupational disease was greatly simplified by using the screening dose for evaluation. A criterion of 95% was recommended as the PC upper limit following consideration for the results of the predicted cases for compensation and the economic circumstances in Korea.