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THE RISKS OF RADIATION WORK : ANALYSIS OF REGISTRY DATA

Objective

It is intended to analyze data from the UK`s National Registry for Radiation Workers with the following aims:
to determine whether there is any evidence of differences in the cause of, and the age at death of, workers exposed to different levels of radiation, and if any differences are found whether it seems likely that they can be attributed to radiation;
if any differences are found which seem likely to be attributed to radiation, to estimate the magnitude of the risk;
to estimate bounds to the possible risk for particular types of malignancy, such as leukaemia;
to compare the mortality experience of radiation workers with national mortality data, and with that of other industrial groups for whom data exist.
Data collected in the United Kingdom's National Registry for Radiation Workers (NRRW) has been analysed. Standardized mortality ratios (SMR) were calcualted to compare the mortality of radiation workers with the general population of England and Wales. The SMR for all causes of death was 85, significantly below 100 at the 0.1% level. The SMR for all malignant neoplasms (86) was similarly below 100. This is a manifestation of the expected healthy worker effect. For all known cases of death except cancers the excess relative risk (RR) was almost exactly zero. For all malignant neoplasms the estimated excess RR was above zero, but was not statistically significant (p=0.10). For all neoplasms of the haematopoietic system the estimated excess RR was positive but not significant (p=0.3). For all leukaemias the excess RR was positive and closer to statistical significance (p=0.10). For leukaemias, except chronic lympatic leukaemia (CLL), the postive excess RR reached statistical significance. The lifetime risk estimate from combined studies (NRRW and United States nuclear worker survey) for all malignant neoplasms is 4.9% Sv{-1} (90% CI less than zero to 18) and for leukaemia is 0.3% Sv{-1} (90% CI less than zero to 1.04).
Current estimates of radiation risk are based mainly on epidemiological studies of populations exposed to high doses and high dose rates. Consequently their use in the protection of those occupationally exposed to low radiation doses involves considerable extrapolation. Studies of radiation workers themselves however can provide a direct, if imprecise, measure of any health effects associated with their radiation exposure.

The National Registry for Radiation Workers (NRRW) was instituted by the NRPB in 1976. There are at present over 95 000 workers within the UK for whom registration has been completed, and agreement in principle exists in respect of some 10 000 more. The median lifetime recorded dose of workers registered is about 10 mSv.

Data collection has been the dominating need in the early years of this study but work on the first analysis is now underway. The analysis will cover a number of areas, proposals for which were described in 1989.

Other work in 1990 and 1991.

There are a number of other specific studies that are also envisaged for this period. These are:
the integration of further personal and dose information into the NRRW database;
improvement of follow up by cross checks between the National Health Service Central Registers and the Department of Social Security;
improvements in data quality by cross checks with integrated employment and radiation dose histories compiled by employers` central records;
consideration of doses from internal emitters. Development of as many as practicable of the following:

a criterion to distinguish those almost certainly not exposed from those possibly exposed;

division of those possibly exposed into low and high dose bands;

reasonable estimates of dose on an individual basis.
an examination of the likely effect of dose record keeping practices on the analysis of data from epidemiological studies.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

NATIONAL RADIOLOGICAL PROTECTION BOARD (NRPB)
Address
Chilton
OX11 0RQ Didcot
United Kingdom