Radiation exposure and cancer incidence in a cohort of nuclear power industry workers in the Republic of Korea, 1992–2005

Meeseon Jeong, Young-Woo Jin, Kwang Hee Yang, Yoon-Ok Ahn, Chang-Yong Cha

This study examines for the first time cancer incidence between radiation and non-radiation workers in nuclear power facilities in the Republic of Korea. Radiation workers were defined as persons who were issued with a dosimeter at nuclear power facilities, until 2005. All analyses were conducted on male workers only (in total 16,236 individuals) because of the sparseness of females. Statistical analyses were carried out using the standardized incidence ratio (SIR), to compare the cancer risks of radiation and non-radiation workers with those of the general population, and the chi(2) trend test was used to investigate any increase in cancer rates with dose. Poisson regression was also used to estimate the rate ratio (RR) and the excess relative risk (ERR) after considering the confounding effect due to smoking. During 1992-2005, 99 cancer cases in 63,503 person-years were observed among 8,429 radiation workers, while 104 cancer cases were observed in 48,301 person-years among 7,807 non-radiation workers. When compared with the site- and age-specific cancer rates for the male population of Korea, the SIR for all cancers combined was 1.07 [95% confidence interval (CI) 0.87-1.30] for radiation workers, and 0.88 (95% CI 0.72-1.06) for non-radiation workers, respectively. The RR for radiation workers compared with non-radiation workers was 1.18 (95% CI 0.89-1.58) for all cancers combined. The SIRs for thyroid cancer were noticeably high for both radiation and non-radiation workers, possibly due to the screening effect, but analysis of the RR showed that there was no statistically significant difference in thyroid cancer incidence rates between the two groups. For lung cancer, radiation workers showed a higher incidence rate as compared to non-radiation workers, with the RR being 3.48 (95% CI 1.19-11.48). A chi(2) trend test showed that there was no evidence for an increase in cancer rate with increasing cumulative dose for all cancers combined (p = 0.5108). The ERR per Sievert was estimated to be 1.69 (95% CI -2.07 to 8.21) for all cancers combined assuming a 10 years lag time. Consequently, a significant excess of cancer incidence among radiation workers in the nuclear power industry in Korea was not observed. Further follow-up and an expansion of the cohort are needed to overcome the lack of statistical power in the study.