Cancer risk in a cohort of Korean radiation workers

Abstract

Introduction : The current radiation protection standards are based on research on Japanese atomic bomb survivors who have experienced acute exposure. Through this, the relationship between radiation exposure and health effects in the medium-high-dose range has been largely established, but the health effects of low-dose radiation exposure are not yet clear. Radiation workers are known to be long-term exposure to low-dose radiation during their working days, and a recent international cohort study involving workers in the nuclear industry in France, UK, and the United States reported the association between low-dose radiation and the risk of death from solid cancer or leukemia. Therefore, concerns over occupational exposure are increasing. In 2017, a cohort was established for the health impact assessment of domestic radiation workers, and the basis for evaluating the risk of cancer in radiation workers was laid by linking dose and cancer registration data.

Objectives : 1) Identifying the characteristics of a cohort of domestic radiation workers and the level of occupational radiation exposure. 2) Comparing and analyzing cancer incidence in the general population. 3) Identifying and quantifying the risk of cancer incidence according to the cumulative dose in the cohort. 4) In addition to exposure to radiation, considering other occupational risk factors affecting cancer development. Methods : The data used when enrolling in the radiation worker cohort established in 2017 were linked with the dose data of individual workers (1984-2016), and cancer registration data (1988-2016). Through this, the demographic and occupational characteristics of the cohort and the distribution of dose during the follow-up period were confirmed. In order to compare cancer incidence with the general population, a standardized incidence ratio(SIR) of sex and age (5 years old) was calculated, and the risk ratio of cancer according to exposure dose was estimated using the Cox proportional risk model. In addition, cancer risk of other occupational risk factors other than radiation exposure was estimated through multivariate regression analysis.

Results : A total of 19,532 radiation workers in 8 industries were followed up. The average follow-up period was 9.3 years, with males (86.8%) and nuclear power plant workers (30.9%) being the most common. The average cumulative exposure dose was 12.2±29.3mSv, which was the highest among non-destructive workers. During the follow-up period, 217 (1.1%) of 19,532 patients developed cancer, and the rate of thyroid cancer was the highest. The standardized incidence of total cancer was significantly lower than that of the general population, but thyroid cancer was significantly higher. There was no significant association between the risk according to the exposure dose. Most of the factors influencing cancer incidence identified in this study were demographic factors. In the result of multivariate analysis corrected for demographic factors, the occupational factor that showed a significant association was employment type (regular/non-regular).

Conclusion: The high incidence of thyroid cancer in radiation workers is likely to be a factor other than dose such as screening effect rather than exposure dose. However, since thyroid cancer is a radiation-sensitive cancer, it is necessary to evaluate the association with dose through continuous research. The overall cancer incidence, which is lower than that of the general population, requires consideration of the effect of healthy workers because the cohort is for young workers with relatively healthy conditions. It was difficult to establish a link between exposure dose and cancer incidence in this study. In the future, it will be necessary to expand the targets of the investigation to retirees who are estimated to have been exposed to high doses in the initial radiation work, and conduct a wide range of health impact assessments including diseases other than cancer through long-term follow-up investigations and linking with various secondary health data. In addition, it is necessary to attempt a detailed evaluation in consideration of other occupational risk factors that are significantly related to the in-depth exposure evaluation through the calculation of organ dose to the human body.