The third analysis of cancer mortality among Japanese nuclear workers, 1991–2002:estimation of excess relative risk per radiation dose

Abstract

The present study estimated excess relative risk per sievert (ERR/Sv) of cancer mortality among the cohort of 200 583 male Japanese nuclearworkers, with an average individual cumulative dose of 12.2 mSv (<10 mSv,75.4%; 100 + mSv, 2.6%), conducting Poisson regression using dose category specific observed andexpected numbers of deaths, and average doses obtained from the official reportof the Radiation Effects Association (REA) on the analysis of mortality ofJapanese nuclear industry workers for 1991–2002, which reported the estimates ofERR/Sv for leukaemia but not for all cancers or any other cancer site. The possibleconfounding biases from drinking alcohol and smoking tobacco were evaluated byexamining the association of cumulative radiation dose with the mortality ofcancers related to drinking or smoking. For leukaemia (80 deaths), the estimate ofERR/Sv was − 1.93 (95% confidenceinterval (CI) = − 6.12, 8.57). For all cancers excluding leukaemia (2636 deaths), while theERR/Sv was estimatedto be 1.26 (95%CI = − 0.27, 3.00), confounding by alcohol consumption was suspected since theERR/Sv estimate of alcohol-related cancers was 4.64 (95%CI = 1.13, 8.91)and the ERR/Sv estimate of all cancers excluding leukaemia and alcohol-related cancers was 0.20 (95%CI = − 1.42, 2.09). In conclusion, confounding by important lifestyle factors related to cancer risk mayhave a substantial effect on risk estimates, especially when conducting studies oflow cumulative dose and, accordingly, low statistical power. Pooled analysis ormeta-analysis of nuclear workers for solid cancers needs to take this point intoaccount.