NRPB

Abstract

Cancer in the offspring of radiation workers: a record linkage study In 1990 Gardner et al [1] published a study suggesting that exposure of fathers to ionising radiation before conception of their children increased the risk of the subsequent development of leukaemia or non-Hodgkin lymphoma (LNHL) in their children; this became known as the `Gardner Hypothesis'. In the original paper increased risks were also seen in other occupational exposures, e.g. chemicals and iron ore work. Following publication of this study the Committee on the Medical Aspects of Radiation in the Environment (COMARE) recommended that studies should be set up to consider any possible effects on the health of the offspring of parents occupationally exposed to radiation. The Department of Health (DH) and Health and Safety Executive (HSE) jointly established the Coordinating Committee on Health Aspects of Radiation Research (CCHARR) to manage Government-sponsored research in this area and two epidemiological studies recommended by COMARE were included in the CCHARR programme. The first of these two epidemiological studies is now complete. A peer-reviewed British Medical Journal [2] article and a NRPB Report have been published [3]. The study is referred to as the Linkage Study. The second study, known as the Nuclear Industry Family Study (NIFS), is due to be published sometime in 1998. The main aim of the study was to test the `Gardner hypothesis' that childhood leukaemia and non-Hodgkin's lymphoma (LNHL) can be caused by paternal exposure to ionising radiation before conception of the child (occupational paternal preconception irradiation (PPI)). A subsidiary aim was to investigate whether such radiation exposure of either parent is a cause of childhood cancer. The study used the register held by the NRPB, on more than 120 000 radiation workers (the National Registry for Radiation Workers (NRRW)) including data on doses, and linked this to registers holding information on childhood cancers, from three organisations namely: the National Registry of Childhood Tumours held by the Childhood Cancer Research Group (CCRG); the Oxford Survey of Childhood Cancers held at the University of Birmingham; and a Scottish study of childhood LNHL by Professor Kinlen of the University of Oxford. Identifying information on the parents of children diagnosed with cancer between 1952 and 1986 in Britain (the cases), were linked with the NRRW. Scottish cases of LNHL diagnosed in the period 1987-1990, which were the subject of a previous study of PPI, were also included. The radiation workers' database was also linked to data on control children, who were matched to the cases by area and time of birth. Information was not available on the children of non-radiation workers employed at the various establishments included in the NRRW. The results show that after excluding cases studied by Gardner and colleagues, fathers of children with leukaemia or non-Hodgkin lymphoma were more likely than fathers of controls to have been radiation workers (relative risk = 1.77, 95% confidence interval 1.05 to 3.03; based on 40 cases and 38 controls) but there was no dose-response relationship for any of the exposure periods studied; indeed the association was most marked for those with a radiation dose below the level of detection. Including the Gardner cases does not alter the relative risk significantly (relative risk = 1.83, 95% confidence interval 1.11 to 3.04; based on 49 cases and 44 controls). No increased risk was found for the group of other childhood cancers. Maternal radiation work was associated with a significant increase of childhood cancer (relative risk = 5.00, 95% confidence interval 1.42 to 26.94; based on 15 cases and 3 controls). Only four of the case mothers and no controls were radiation workers during pregnancy. As the results showed no PPI dose-response relationship, the hypothesis that PPI is a cause of childhood leukaemia and non-Hodgkin lymphoma is not supported. The observed general increased risk which is independent of dose to fathers may be a chance finding or result from other agents. Any increased risk for the children of fathers who are radiation workers is small in absolute terms. In Britain the average risk by age 15 years is 6.5 per 10 000; the authors' best estimate is that the increase is 5.4 per 10 000. For mothers, the numbers are too small for reliable estimates to be made.