Study question. Is protracted exposure to low doses of ionising radiation associated with an increased risk of solid cancer?
In this cohort study, 308 297 workers in the nuclear industry from
France, the United Kingdom, and the United States with detailed
monitoring data for external exposure to ionising radiation were linked
to death registries. Excess relative rate per Gy of radiation dose for
mortality from cancer was estimated. Follow-up encompassed 8.2 million
person years. Of 66 632 known deaths by the end of follow-up, 17 957
were due to solid cancers.
Study answer and limitations.
Results suggest a linear increase in the rate of cancer with increasing
radiation exposure. The average cumulative colon dose estimated among
exposed workers was 20.9 mGy (median 4.1 mGy). The estimated rate of
mortality from all cancers excluding leukaemia increased with cumulative
dose by 48% per Gy (90% confidence interval 20% to 79%), lagged by 10
years. Similar associations were seen for mortality from all solid
cancers (47% (18% to 79%)), and within each country. The estimated
association over the dose range of 0-100 mGy was similar in magnitude to
that obtained over the entire dose range but less precise. Smoking and
occupational asbestos exposure are potential confounders; however,
exclusion of deaths from lung cancer and pleural cancer did not affect
the estimated association. Despite substantial efforts to characterise
the performance of the radiation dosimeters used, the possibility of
measurement error remains.
What this study adds.
The study provides a direct estimate of the association between
protracted low dose exposure to ionising radiation and solid cancer
mortality. Although high dose rate exposures are thought to be more
dangerous than low dose rate exposures, the risk per unit of radiation
dose for cancer among radiation workers was similar to estimates derived
from studies of Japanese atomic bomb survivors. Quantifying the cancer
risks associated with protracted radiation exposures can help strengthen
the foundation for radiation protection standards.
Funding, competing interests, data sharing.
Support from the US Centers for Disease Control and Prevention;
Ministry of Health, Labour and Welfare of Japan; Institut de
Radioprotection et de Sûreté Nucléaire; AREVA; Electricité de France; US
National Institute for Occupational Safety and Health; US Department of
Energy; and Public Health England. Data are maintained and kept at the
International Agency for Research on Cancer.