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Summary of the study

Objectives of the study

1. To test the "Gardner hypothesis" that childhood leukaemia and non-Hodgkin lymphoma (LNHL) can be caused by paternal preconception irradiation (PPI)
2. To investigate whether radiation exposure of either parent is a cause of childhood cancer.

Nature of study

• A case-control study in GB involving 35,949 children with cancer, together with matched controls.
• Examination was made of parental employment as a radiation worker, cumulative dose of external ionising radiation over various periods, and pregnancy dose of radiation.

Findings of the study

• Fathers of children with LNHL were significantly more likely than fathers of controls to have been radiation workers (relative risk = 1.83, 95% level)
• For the minority of workers monitored for internal exposure the relative risk rose to 2.91, also statistically significant at the 95% level.
• There was no dose-response relationship for any of the periods studied.
• There was no increased risk for other childhood cancers.
• Maternal radiation work was associated with an increase of LNHL (relative risk = 4.0, not statistically significant due to small numbers of cases), and of Other Childhood Cancers (relative risk = 5.5, statistically significant at 95% level)

Official Conclusions of the study

• The results do not support the hypothesis that paternal preconception irradiation is a cause of childhood LNHL.
• The observed associations may be chance, or due to exposure to infective or other agents.
• In particular, high levels of population mixing among radiation workers might involve increased exposure to a leukaemogenic agent.
• The raised risks among the children of female radiation workers may also be chance, due to some other agent, or related to exposure to infection promoted by population mixing.
• If there is any increased risk for children of male radiation workers, it is small, rising from a risk by age 15 of 6.5 per 10,000 to 11.9 per 10,000.

Critique of the study

The overwhelming impression from reading this report is that the official conclusions do not represent, nor follow logically from, the findings. This type of misrepresentation and misinterpretation of facts is not unusual. For example the Berkshire Health Authority report of July 1997 on Leukaemias in Newbury contained an Executive Summary and Conclusions which equally failed to summarise the body of the findings.

I would propose an alternative set of Conclusions which more adequately represent the facts as presented in the report.

True Conclusions

1. The risk of contracting childhood leukaemia by age 15 is almost doubled for the offspring of male radiation workers, from 6.5 per 10,000 to 11.9 per 10,000. Doubling is a large, not a small, increase in risk.
2. Fathers of children with LNHL are considerably more likely than fathers of controls to be radiation workers (relative risk = 1.83, statistically significant at 95% level)
3. There is no evident dose-response relationship whereby exposure to higher external doses as measured by film badges leads to higher risk.
4. This lack of relationship does not appear to actively support the "Gardner" hypothesis of paternal preconception irradiation (PPI)
5. The findings do not however exclude the possibility of PPI causing LNHL, because exposure to internal radioisotopes may be responsible. Exposure to such internal doses was not measured in over 75% of the cases in this study. Interestingly, in the cases where workers had been monitored for internal exposure, the relative risk was even higher at 2.91, compared to the 1.61 for those not so monitored.
6. The validity of external film badges as a relevant and meaningful measure of radiation doses should therefore be seriously questioned.
7. Maternal radiation work is associated with an increase of LNHL (relative risk = 4.0, not statistically significant due to small numbers of cases), and of Other Childhood Cancers (relative risk = 5.5, statistically significant at 95% level)
8. There is no evidence within these findings to support other theories for the cause of LNHL and other childhood cancers.
9. The report's conclusion that "in particular, high levels of population mixing among radiation workers might involve increased exposure to a leukaemogenic agent" is speculative, unsupported by any evidence and illogical.

Exposure to internal radioisotopes

It is now increasingly recognised that there is no safe dose of radiation. In the BBC Panorama programme of 26 January 1998, Dr Roger Cox of the National Radiological Protection Board admitted that however small the dose, there is a finite risk. Indeed, the NRPB recommended 10 years ago that the recommended maximum annual dose be reduced from 50 to 15 milisieverts.

Recent research in the UK and USA, reported in "New Scientist" Nov 1997, indicates that radiation can cause damage to DNA which is passed and amplified from one generation to the next.

In particular there is growing concern about the effects of internal radiation. As far back as 1958 a United Nations conference emphasised the dangers of this, especially through the inhalation and ingestion of particles. Research in 1997 reported in the International Journal of Radiation Biology indicated that a single alpha particle may be carcinogenic.

Unfortunately, such internal radiation has not been routinely measured for radiation workers. Panorama highlighted the case of Bill Neilson, a radiation worker whose official records, as measured by film badges, showed a lifetime dose of 108 milisieverts. After his death from leukaemia, the post-mortem revealed a true dose of an incredible 15,000 milisieverts.

Looking at external doses alone has been likened to clapping a blind eye to the telescope.

Roman et al. in their study of LNHL in West Berkshire and Hants suggested that "the possibility that the effects could be due to internal contamination by radioactive substances.... should be explored"

Rooney et al. examined prostate cancer risk in nuclear workers and found no simple dose-response relation with external film badge doses. However, they found evidence of increased risk with internal exposure to isotopes, including a relative risk of 14.2 for the radioactive gas Tritium.

Against this background it is interesting to note again that the current report found the highest relative risk of 2.91 for workers who had been monitored for internal radiation.

Dr Chris Busby in a letter to the BMJ makes the telling point that if internal exposure is the cause, then the true relative risks are far higher than those shown, because the control groups were drawn from the local population surrounding the nuclear sit es, and these people would themselves be exposed to higher doses of internal radiation than the general population.

Population mixing as the cause of LNHL

This theory originated in the idea that an influx of new workers into an isolated rural area introduced onco-infective agents into a local population which had little resistance to infection. This may have been partially true decades ago when the first n uclear power stations were constructed in remote places, but is implausible when considering our local situation around Aldermaston, Burghfield, Harwell etc. Berkshire and Oxfordshire have been corridors of enormous population mixing for centuries.

There is no evidence that the amount of mixing among radiation workers is any greater than that in any modern commercial or industrial concern. "Professional" staff would meet with colleagues from other sites, but not to any greater extent than similar s taff in any other knowledge-based organisations. "Manual" staff would arguably mix very little with others - visitors of any type are rarely encouraged to visit nuclear sites!

Furthermore, emplo yees at radiation sites do not live on site, they live in surrounding towns and villages where they mix socially (and infectively!) with other non-radiation workers. It is important to remember that the control groups for this study lived in exactly the same places as the radiation workers. The only factor differentiating the two groups is not the degree of population mixing, but the fact that one group worked in a radiation environment.

All in all, population mixing seems an unlikely explanation and an all too easy excuse for ignoring the far more logical and obvious cause.

Footnote

The "New Scientist" editorial 15 November 1997 commented "some epidemiologists are saying the transmission hypothesis has had its day and should be laid to rest..... Such complacency is premature ..... it is as foolish for the nuclear industry to claim that radiation is not to blame for the excess of leukaemias suffered by its workers' children as it is for anti-nuclear campaigners to assert the opposite"

Particular note re: Newbury

The above debate is of great importance with regard to "childhood" leukaemias and cancers and probably by extension to "adult" cancers. It should be remembered however that the particular excess in Newbury is of "adult" leukaemias, especially Myeloid Leukaemia among youngish adults.

Most of the cases in the heart of the "cluster" are not among radiation workers or their offspring.

Some authorities argue that residents of Newbury, in common with other parts of the Thames valley, are exposed to high levels of radioactive discharges emanating periodically from the several nuclear establishments ringing the area. Such discharges could lead to the inhalation or ingestion of radionuclides.

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Revised 29 Jan 1998 RRC