International Study of Cancer Risk Among Radiation Workers in the Nuclear Industry
The study 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.
A summary paper - Cardis, E, Vrijheid, M, Blettner, M, et al . Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries. - can be found on the BMJ Website, www.bmj.com. 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.