UK
International Study of Cancer Risk among Radiation Workers in the Nuclear Industry
By Health Protection Agency
Jul 7, 2005, 18:15

International Study of Cancer Risk among Radiation Workers in the Nuclear Industry

HPA welcomes the publication of a large study1 of nuclear workers in 15 countries, including the UK . The results suggest there is a small excess risk of cancer due to radiation exposure in the workplace. The estimated risks are higher than, but statistically compatible with, the values upon which current radiation protection standards are based. Whilst it is estimated that around 1-2% of cancer deaths among workers in this study may be attributable to radiation, many of the higher exposures arose many years ago when protection standards were less stringent than they are today.

Background

The health risks of ionising radiation, derived from studies of groups such as survivors of the atomic bombings of Hiroshima and Nagasaki, have been a major input to setting radiation protection standards. There has been concern for many years about the extent to which findings from people who received relatively high radiation doses in a short period are applicable to lower doses received over a long period. Studying the health of radiation workers, who have received generally low doses over a prolonged period, can provide more direct information about the health risks of low doses of radiation. However, worker studies need to be very large to detect what may well be small risks and to compare these results with risks predicted from groups such as the Japanese atomic bomb survivors. To obtain more precise results, researchers need to increase the numbers by looking at workers across a number of different employers, particularly in the nuclear industry2 . Within the UK , the Radiation Protection Division of the Health Protection Agency operates the National Registry for Radiation Workers (NRRW), which includes many workers who are, or had been, employed in the nuclear industry. This study has already provided an improved understanding of chronic low dose risks3,4 . However, a larger study has now been published that combined data from 15 countries, including data from the NRRW.

International Study

This study1 was set up in the early 1990s and was co-ordinated by the International Agency for Research on Cancer (IARC), an agency of the World Health Organization. The study involved researchers from 15 countries � mostly in Europe, North America and Asia - who conducted studies in their own countries of cancer mortality among radiation workers employed in the nuclear industry. These workers were employed in nuclear power generation, nuclear research, waste management or the production of nuclear fuel, isotopes or weapons. The UK provided anonymised data to IARC on nuclear industry workers from the most recent analysis of the NRRW4. Some of the data from other countries, such as the USA, were also based on existing studies, whilst the setting-up of an international study provided the impetus for new research in other countries, such as France and Japan .

The study included about 400,000 workers, mostly men, who had been monitored for exposure to external radiation. Workers who had significant potential for internal radiation exposures were not included, largely because of variability in the way that these exposures had been recorded. The analyses looked to see if there was any trend in the risk of cancer death, according to the level of the recorded cumulative dose from external radiation.

For all cancers other than leukaemia taken together, the risk of death increased to a statistically significant extent with increasing radiation dose. Since data on individual smoking habits were not available, it is difficult to know how smoking might have affected these results. However, the findings for specific causes of death do indicate that smoking may explain partly, but not entirely, the increased risk seen for all cancers other than leukaemia. For leukaemia, there was also an indication of an increasing trend in risk with increasing radiation dose, but here the evidence was weaker and did not reach conventional levels of statistical significance.

Notwithstanding the size of the study, it was not possible to quantify the risks from occupational radiation exposures precisely. The findings were consistent with risks that ranged from values lower than those derived by linear extrapolation from A-bomb survivors data, up to values that exceed this extrapolation by a factor of six for cancers other than leukaemia and nearly three for leukaemia. Based on the best estimates of risk, about 1 to 2% of the cancer deaths among workers in this study may be attributable to radiation exposure. However, many of the higher exposures were received in the early years of the nuclear industry, when protection standards were less stringent than they are today.

More detailed results for specific types of cancer, specific countries and other factors will be published in a longer report due to appear later this year.

Future work

The Health Protection Agency will continue its efforts to obtain more precise information on the risks of occupational radiation exposure through a new analysis of the NRRW, based on an expanded group of around 180,000 UK workers (compared with about 125,000 workers studied previously 4 ) and a longer period of follow-up. This analysis � which is currently in progress - will also examine the incidence of cancer, in addition to cancer deaths. Subject to the agreement of the workforces, data from this new UK analysis may also be included in a possible extension of the international study.

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