Professor Nicholas D Priest, Middlesex University

Project summary

Exposure to high dose radiation (either by exposure during medical radiography or as a consequence of nuclear accidents or explosions) is one of the few proven risk factors for childhood leukaemia. It is thought – but not yet established - that protracted exposure to low dose environmental radiation could also be a risk factor.

Studying the association between leukaemia risk and such low dose radiation (which may come from naturally occurring radon gas or from radionuclides released to the environment by the nuclear industry) is problematic due to the combination of the relative rarity of the disease and the low variation in radiation dose in most populations.

There are also inevitably difficulties of access to determine radon doses in homes and the complicating factor that adverse results of radon surveys may reduce property values. The studies that have taken place have produced inconsistent results, fuelling controversy.

We funded Professor Priest to carry out a feasibility study to see whether it might be possible to overcome these methodological problems.

The study was undertaken in the uranium provinces of southern Kazakhstan and Kyrgyzstan, which are known to be regions of high natural radioactivity. It was speculated, based on limited survey data, that the radiation doses in these areas would be sufficiently high and sufficiently variable to facilitate a powerful study in which the radiation doses to leukaemic children and their siblings could be compared with those received by control children admitted to hospital for conditions other than leukaemia/cancer.

The feasibility study aimed to confirm radiation exposures and also to assess the reliability of childhood cancer diagnoses in the region.

Working in association with regional childhood cancer treatment centres in both countries, teams of investigators planned to visit approximately 100 families chosen randomly from hospital records.

Many problems were encountered including that Kazakh and Kyrgyz populations are highly mobile and the visiting teams could not locate many families; and that the vast tracts of often poorly populated territory over which families were spread meant that it took a great deal of time to distribute and collect the radiation meters.

In total 59 families were monitored successfully. However the radiation doses, although higher than might be expected in the UK, were not as high as expected and variability between subjects was generally low.

Overall, the results suggest that the central Asian populations studied receive similar annual radiation doses to those received by other populations living in some other areas with enhanced natural radioactivity and that the study of these populations would be unlikely to provide the conclusive evidence needed to justify progressing to a full study.

Implications

The results of this study lead to the clear conclusion that some of the necessary hypotheses cannot be supported and so these exposed populations do not provide the opportunity for a suitably powerful full study to be set up to answer the questions on radiation risk on childhood leukaemia.

This is unfortunate for advancing understanding of the aetiology of leukaemia and quantifying environmental radiation as a risk factor. However by identifying this obstacle before large amounts of money were spent on planning and/or undertaking a full epidemiological study, the project has been highly cost-effective in what is has achieved.

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