Cancer Death Risk From Low-Dose Radiation Is Underestimated, Study Suggests

A new study suggests that prolonged exposure to low-dose radiation – such as for workers in the nuclear industry – is associated with an increased risk of death from cancer. The research is published in the British Medical Journal.

Risks of radiation exposure

Studies of survivors of the Hiroshima and Nagasaki atomic bombs during the Second World War have provided valuable knowledge on how radiation dosage affects the risk of developing cancer.

These studies serve as the basis for radiation protection required by workers who are regularly exposed to low-level radiation, such as nuclear workers and some healthcare staff.

However, these radiation protection standards are drawn from people exposed to acute, high doses of ionizing radiation as opposed to prolonged, low-dose and low-rate exposure.

The International Nuclear Workers Study (INWORKS) was established to gain greater knowledge relating to the risks of both cancerous and non-cancerous diseases linked to chronic exposure to low doses of ionizing radiation. This collaborative project monitors data from over 300,000 workers in the nuclear industries in France, the United Kingdom and the United States.

The latest update in the INWORKS study tracked and analyzed deaths among these workers who had individual monitoring data available for ionizing radiation exposure.

Cumulative low exposure increases risk

During the monitoring period from 1944–2016, a total of 103,553 workers died. Of these, almost 30,000 were a result of solid cancers – i.e., cancers not of the blood.

The researchers were able to calculate the risk of death from solid cancers based on a person’s exposure to radiation in the past 10 years, estimating that for every cumulative unit of radiation (per Gray, or Gy) that workers were exposed to, the risk of death from solid cancer increased by 52%.

Limiting the analysis to those exposed to the lowest cumulative doses of radiation (0–100 mGy) doubled the risk of death per each Gy absorbed. Excluding deaths from lung cancers, which might be linked to smoking or asbestos exposure, had little effect on the strength of the association.

The authors note some limitations to the study, speculating that workers employed in the infancy of the nuclear industry may have poor estimates of exposure despite efforts to account for improvements in monitoring technology. However, a separate analysis of deaths only for workers employed in more recent years found an even higher association per unit Gy absorbed – suggesting that workers employed early in the study period did not drive the increased risk across the whole cohort. There was also no individual-level data on several potentially confounding factors such as smoking status.

“People often assume that low dose rate exposures pose less carcinogenic hazard than the high dose rate exposures experienced by the Japanese atomic bomb survivors,” the researchers write in the paper. “Our study does not find evidence of reduced risk per unit dose for solid cancer among workers typically exposed to radiation at low dose rates.”

“The findings, which are in line with other recent studies, support the existence of cancer risks from low doses of ionizing radiation, and that the risks might be higher than we had previously expected,” said Dr. Amy Berrington, professor of clinical cancer epidemiology at the Institute of Cancer Research, London, who was not involved in the study. “However, it is important to note that the absolute risk of cancer from low doses of ionizing radiation is still very small – double a small risk is still a small risk.”

Further verification required

“This study suggests that the risk of cancer may increase more rapidly with exposure to ionizing radiation than previously thought, but more studies of this kind are needed to verify this result,” said consultant medical physicist Dr. Heather Williams, who was not involved in the study.

The study’s authors hope organizations responsible for protection standards, such as the International Commission on Radiological Protection, will use these findings to inform risk assessments of low-dose and low-rate radiation and provide safe limits for workers.

Reference: Richardson DB, Leuraud K, Laurier D, et al. Cancer mortality after low dose exposure to ionising radiation in workers in France, the United Kingdom, and the United States (INWORKS): cohort study. BMJ. 2023;382:e074520. doi: 10.1136/bmj-2022-074520

This article is a rework of a press release issued by the University of California, Irvine. Material has been edited for length and content.