C R Muirhead, J A O’Hagan, R G E Haylock, M A Phillipson, T Willcock, G L C Berridge and W Zhang
Publication date: December 2009
Mortality and cancer incidence have been studied in a cohort of about 175,000 persons on the National Registry for Radiation Workers (NRRW) who were followed until the end of 2001. This analysis is based on a larger cohort and nine years’ further follow-up compared with the 2nd NRRW analysis, and includes cancer registration data for the first time. As in previous NRRW analyses, total mortality and mortality from major causes were less than would be expected based on rates for England and Wales; the Standardised Mortality Ratio (SMR) for all causes was 81, whilst the SMR for all malignant neoplasms was 84. This “healthy worker effect” was still present after adjustment for social class. The only cause for which mortality was statistically significantly greater than expected from national rates was pleural cancer, probably reflecting exposure to asbestos.
Within the cohort, there was borderline evidence of an increasing trend in total mortality with increasing external radiation dose. Much of the evidence for this trend related to cancer. Mortality and incidence from both leukaemia excluding chronic lymphatic leukaemia and the grouping of all malignant neoplasms other than leukaemia increased to a statistically significant extent with increasing dose. The corresponding central estimates of the trend in risk with dose were similar to those for the survivors of the atomic bombings of Hiroshima and Nagasaki, whilst the 90% confidence intervals for the NRRW trends excluded values more than about 2-3 times greater than the A-bomb risk estimates as well as values of zero or less. Whilst there was some evidence of an increasing trend with dose in mortality from all circulatory diseases combined, the irregular pattern in risk with dose and similarities with the corresponding pattern for lung cancer suggest that this finding may, at least in part, be due to confounding by smoking.
In contrast, both for mortality and incidence, the trend with dose in the risk of all malignant neoplasms other than leukaemia was maintained when lung and pleural cancer were excluded from this disease grouping, so indicating that the trend is not an artefact due to smoking. Statistically significantly increasing trends with dose were seen for multiple myeloma (based on incidence data) and for cancers of the rectum (based on both mortality and incidence data), larynx (based solely on mortality data), all skin combined and non-melanoma skin specifically (based on incidence data) and uterus (based on mortality and - for endometrial cancer - incidence data); some of these results might be chance findings or artefacts.
This analysis provides the most precise estimates to date of the risks of mortality and cancer incidence following occupational radiation exposure and strengthens the evidence for raised risks due to these exposures. The cancer risk estimates obtained here are consistent with values used by national and international bodies in setting radiation protection standards. Continued follow-up of these workers should be valuable to see whether radiation-associated risks vary over time or by age, and to study specific cancers and causes of death in more detail.
Last reviewed: 8 March 2010