LAUSR

PURPOSE While some evidence of an effect of radiation exposure on respiratory disease at low dose levels has now emerged, there is heterogeneity in the risks between different studies and countries. In this paper, we aim to show the effect of radiation on three different sub-types of respiratory disease mortality through the analysis of the NRRW cohort in UK. MATERIALS AND METHODS The NRRW cohort consisted of 174,541 radiation workers. Doses to the surface of the body were monitored using individual film badges. Most of the doses are associated with X-rays and gamma rays and to a less extent of beta and neutron particles. The overall mean 10 year lagged lifetime external dose was 23.2 mSv. Some workers were potentially exposed to alpha particles. However, doses from internal emitters were not available for the NRRW cohort. 25% male workers and 17% female workers were identified as being monitored for internal exposure. The Poisson regression methods for grouped survival data with a stratified baseline hazard function were used to describe the dependence of the risk on cumulative external radiation dose. The disease was analysed by the following subgroups: Pneumonia (1066 cases including 17 cases of influenza), COPD and allied disease (1517 cases) and other remaining respiratory diseases (479 cases). RESULTS There was very little radiation effect on pneumonia mortality, but evidence of a reduction in mortality risk for COPD and allied disease (ERR/Sv= -0.56, 95%CI: -0.94, -0.06; P = 0.02) and an increase in risk for other respiratory disease mortality (ERR/Sv = 2.30, 95%CI: 0.67, 4.62; P = 0.01) with increasing cumulative external dose were observed. The effects of radiation were more prominent amongst workers monitored for internal exposure. The reduction in mortality risk of COPD and allied disease per cumulative external dose was statistically significant for the radiation workers monitored for internal exposure (ERR/Sv=-0.59, 95%CI: -0.99, -0.05; p = 0.017) but not significant among the workers who were not monitored (ERR/Sv=-0.43, 95%CI: -1.20, 0.74; p = 0.42). A statistically significant increased risk was observed for other respiratory diseases among monitored radiation workers (ERR/Sv = 2.46, 95%CI: 0.69, 5.08; p = 0.019), but not among unmonitored workers (ERR/Sv = 1.70, 95%CI: -0.82, 5.65; p = 0.25). CONCLUSION The effects of radiation exposure can be different depending on the type of respiratory disease. No effect was seen in pneumonia; a reduction in mortality risk of COPD, and increased mortality risk of other respiratory diseases were observed with cumulative external radiation dose. More studies are needed to verify these findings.