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International collaborative study of cancer risk among nuclear industry workers


During the reporting period, the International Collaborative Study on Cancer Risk among Radiation Workers in the Nuclear Industry was set up in the following 12 countries: Australia, Belgium, Canada, Finland, France, Germany, Japan, Spain, Sweden, Switzerland, the UK and the USA. In addition, the feasibility of extending the study to Hungary and the Slovak Republic was established. In the USA, the study was extended to two new cohorts, that of Portsmouth Navel Shipyard employees and that of Idaho National Engineering Laboratory workers.

A common core protocol is in use in all countries to ensure comparability of study design and analyses. The document outlining the detailed procedures for setting up the study and for data collection was prepared and distributed. Throughout the reporting period, IARC staff carried out site visits to participating countries, as needed, to review difficulties encountered in setting up of cohorts, collecting basic employment and dosimetric data and carrying out long-term mortality follow-up, and providing assistance to National Study Group members with problems of data collection and analysis. After two years, a revised and expanded version of the Procedures Document was prepared by IARC to reflect changes in data collection approaches which had taken place at the national level because of the logistic or legal difficulties encountered.

In addition, protocols for studies aimed at assessing and ensuring the comparability - across countries and over time - of occupational external dose estimates and of cause of death coding have been prepared by IARC and are being implemented in participating countries.

A critical review of existing software for management and analysis of the combined data set has been carried out at IARC, and the database is being redesigned for greater flexibility and speed of data retrieval and analysis. Approaches for routine validations and basic analyses are being developed and compared. Simple, portable software for trend test analyses is being written and will be sent to collaborators.

At the national level, progress has been dependent on logistic, legal and financial problems. Permission from appropriate authorities for collecting the information required for the purpose of the International Collaborative Study have been obtained from all countries. In some countries, obtention of the required authorisations has considerably delayed the beginning of the study.

Construction of cohorts has been completed in all countries except Spain. The collection, computerisation and validation of entry data has started in all 12 countries. Mortality follow-up has also started in most countries. Follow-up for mortality is near complete and analyses are starting in Finland, Japan, Sweden and the UK. Follow-up for cancer incidence has been completed in Finland and Sweden.

In Hungary and the Slovak Republic, the feasibility study was successful. Results of additional pilot studies are awaited before the detailed procedures documents are finalised. Construction of the cohorts has been carried out and the progress of these studies is expected to be rapid.
Radiation risk assessment is mainly based at present on epidemiological studies of subjects receiving moderate or high doses of ionizing radiation over a short time period and on large, long-term animal carcinogenicity experiments. The use of these results to set protection standards for low dose chronic exposure requires the use of controversial extrapolation models which cannot be validated on the basis of these data alone. Epidemiological studies of populations exposed chronically to low doses of ionizing radiation are necessary to assess the adequacy of the extrapolation models and to guide radiation protection practice. Populations of workers occupationally exposed to ionizing radiation in the nuclear industry are ideal for this purpose because of the detailed dosimetric and employment records which are kept in this industry. Several studies of cancer mortality among these workers have been carried out in the last decade; data from most of these studies are currently being combined at IARC. Larger numbers of subjects are required, however, if the estimates of risk are to be sufficiently precise for confident scientific and regulatory use.
The current proposal concerns the setting up and coordination of an international collaborative study of cancer risk among nuclear industry workers from 12 countries (eight from Europe, including six EEC member states). A detailed feasibility study has been carried out with the conclusion that a retrospective cohort study is feasible in all 12 countries and desirable for the purpose of radiation protection. A common core protocol has been finalized and agreed by all 12 countries. If all of them participate, the study will cover approximately 900 000 workers with yearly individual dose estimates. It will substantially increase the power for direct estimation of the effects of low dose chronic exposure over that of the current studies and will allow the ruling out of material differences
between the actual risk at low doses and the current predictions from the high or moderate dose studies. A detailed dosimetric study will be carried out in parallel in order to ensure the comparability of dose estimates across time and across facilities.


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