select search filters
briefings
roundups & rapid reactions
before the headlines
Fiona fox's blog
A study published in the BMJ looks at cancer mortality after low dose exposure to ionising radiation in workers in France, the United Kingdom, and the United States.
A spokesperson from the Society for Radiological Protection, said:
“This study is one of a number which shows that the risk of cancer at low dose radiation exposure could be higher than previously reported. There are a number of unanswered questions with this study (and others like it) and until these are answered the current Radiological Protection system of protection is appropriate as doses should be managed to As Low As Reasonably Practicable (ALARP).”
Prof Amy Berrington, Professor of Clinical Cancer Epidemiology, The Institute of Cancer Research, London, said:
“This study combines data from some of the highest quality nuclear worker studies available. The authors have assessed a wide range of potential biases in these observational studies and their conclusions are backed up by solid data and careful analysis.
“It is still a widely held theory that there is no risk of cancer from low-doses of radiation, or that the risks taper off rapidly as radiation dose goes below a certain point. These assumptions come from studies of survivors of the Japanese atomic bombings, who were exposed to higher doses of radiation.
“This study instead looked at data from nuclear workers in France, the UK and the US to better understand the risks associated with lower doses of radiation. The findings, which are in line with other recent studies, support the existence of cancer risks from low-doses of ionising radiation, and that the risks might be higher than we had previously expected.
“However, it is important to note that the absolute risk of cancer from low-doses of ionising radiation is still very small – double a small risk is still a small risk. For example, for every 1,000 people exposed to 100mSv of ionising radiation – with most nuclear workers currently being exposed to less than 10mSv – there could be 10 extra cancer deaths rather than 5 extra cancer deaths, on top of over 200 expected cancer deaths that will occur due to other causes.
“We expect this data will be taken into consideration by authorities setting safe radiation limits for workers.”
Mr Jim Thurston FIPEM, FSRP, Radiation Protection Expert, the Institute of Physics and Engineering in Medicine; and Head of Healthcare Technology, Dorset County Hospital NHS Foundation Trust, said:
“This is the latest in a large number of papers published over many years that attempts to consider whether the Life-Span Study of the effects of the high radiation doses and dose rates received by survivors of the atomic bombs at Hiroshima and Nagasaki can be directly related to the effects of exposure to low doses and dose rates from occupational, medical and other sources.
“This study, as with a number of others, presents data that seems to show that there is a difference in the effects of radiation exposure at low doses and that the consequential risk of cancer is higher than expected.
“Other studies over the years have demonstrated data to show the exact opposite, and it may be argued that the current model of directly relating the risk of cancer to the radiation dose received – the Linear Non-Threshold model – steers an appropriate middle path between these conflicting sets of data.
“In any case, this paper, together with all these studies, suffers from the large range of confounding factors. And whether or not those factors have been appropriately dealt with is the key issue in deciding how much weight to attribute to the conclusions drawn when considering any changes to the framework for radiation protection and associated regulatory controls.”
Matthew Dunn, Vice President Medical Physics, the Institute of Physics and Engineering in Medicine, said:
“This study provides good evidence that even low doses of radiation in medical, occupation or environmental settings have the potential to cause cancer. The protection of patients and staff by the careful optimisation of radiation exposure remains an important function to reduce risks as far as practical in the medical sector.”
Dr Heather Williams, Consultant Medical Physicist and Nuclear Medicine Group Leader, Christie NHS Foundation Trust, said:
“INWORKS is a long-term follow-up study of the health of radiation workers in three nations over more than a decade, including over 300,000 workers in the nuclear industry. The study team have gone to considerable lengths to accurately assess workplace exposure and identify how many more people have died from cancer which is likely to have resulted from this exposure. The models used make reasonable assumptions where data is not available, and the results are convincing.
“This study provides further evidence to support current understanding that even a small exposure to ionising radiation causes a small amount of damage which can potentially develop into something very serious, which applies to all forms of ionising radiation and not just those exposures in the context of the nuclear industry. Such findings lend further support to the established radiation protection principles that radiation exposures need to be justified and that radiation doses from those exposures should be kept “as low as reasonably achievable” (ALARA). This study suggests that the risk of cancer may increase more rapidly with exposure to ionising radiation that previously thought, but more studies of this kind are needed to verify this result.”
Prof Richard Wakeford, Honorary Professor in Epidemiology, Centre for Occupational and Environmental Health, University of Manchester, said:
“Epidemiological studies of health effects in radiation workers have the potential to reveal the risks associated with a series of many small radiation doses received in the workplace. But the predicted additional risks are small so that large numbers of workers are required to find the statistical signal against the background noise. INWORKS is an example of such a large study, composed of nuclear workers from the UK, USA and France. However, analysing a large dataset of workers poses challenges, such as ensuring the accuracy of radiation doses received over long periods, particularly during the early years of operations at nuclear facilities when doses tended to be higher but less reliably recorded.
“Although the latest results from INWORKS for the risk of solid cancer mortality among nuclear workers indicates an increased risk associated with the dose accumulated occupationally, some caution is required in drawing conclusions about the levels of radiation-associated risk found and therefore whether there is any discrepancy with the levels conventionally derived from the experience of the Japanese atomic bomb survivors. The patterns of risks among the workers pose questions that will require answers before reliable conclusions can be drawn. For example, why is the risk estimate for workers first employed before 1958 about one-sixth of that for workers first employed after 1957, a statistically significant difference? Early workers tended to receive higher doses than later workers, so is this notable difference in risk estimates due to dose recording inaccuracies, doses from other types or radiation that have not been accounted for, the impact of non-radiation risk factors, or what?
“The uncertainties in the interpretation of the latest INWORKS results are largely a reflection of those present in the national studies, in particular, the UK and US studies. Hopefully, substantial effort will be directed towards addressing these outstanding questions so that increased confidence can be placed in the levels of risk obtained from radiation worker studies because these studies are important for the understanding of the risks posed by low doses of radiation.”
Prof Jim Smith, Professor of Environmental Science, University of Portsmouth, said:
“This paper is a major update on an important study of cancer risk in over 300,000 nuclear industry workers in three different countries. The estimate of cancer risk from a particular dose of radiation is primarily (but not wholly) based on the long term study of survivors of the Hiroshima and Nagasaki atomic bomb survivors. Survivors of the atomic bombs received what is called an acute dose of high energy radiation – they received most of their radiation dose within the first second of the bomb explosions. There has for a long time been a question about how to use data from these acute exposures to estimate cancer risk in people exposed to lower doses over a long period of time such as those from natural sources of radiation, or radiation in the workplace – so called “chronic” low dose radiation. It is has for a long time been assumed in radiation protection that chronic, low dose radiation exposures, per amount of absorbed radiation, are 1.5-2 times less damaging than acute exposures such as those to the atomic bomb survivors. The evidence from this important study gives strong support to evidence built up in recent decades that in fact chronic, long term dose rates are likely to be just as damaging in terms of cancer risk as acute ones, per amount of radiation absorbed in the body.
“The study findings are consistent with the Japanese atomic bomb data without the application of a reduction in risk for chronic low doses. There is less strong evidence that there may even be higher risk for chronic low dose exposures. The findings of this study have important implications for radiation protection and will need to be taken into account when current risk factors for radiation exposure are reviewed.
“Although smoking as a risk factor has not directly been accounted for in the study, the authors present good evidence that this has not biased results. It is less clear, though, how at low dose rates natural radiation and medical X-ray radiation have been accounted for in the study. These could have important implications in the low dose rate range since they could significantly add to radiation exposure to those workers exposed to lower occupational doses.
“It is important to note that although this study gives strong evidence for an increased cancer risk from radiation in the workplace, absolute risks to radiation workers are low in comparison to other factors important for health (for example whether a person smokes, whether they have a healthy diet, body mass index, exercise etc.). Radiation doses to nuclear industry workers are currently on average very low.”
Prof Paul Pharoah, Professor of Cancer Epidemiology, Cedars-Sinai Medical Center, said:
“Studies of the survivors of the atomic bomb in Japan have shown quite clearly that high doses of radiation cause a long-term increase in the risk of cancer. These studies have informed guidelines on the effects of low-dose exposure to ionising radiation. In this study the researchers have used records of low-doses radiation exposure in workers in the nuclear industry to estimate the increase in risk cause by long-term low dose exposure.
“The study has been carefully conducted and analysed and provides estimates of the relative increase in cancer risks of radiation doses from a few milli Grays (mGy) to one Gray (a mGy is one thousandth of a Gy). A chest Xray is equivalent to about 0.1 mGy, a breast mammogram is about 0.2 mGy, and a CT scan of the chest is equivalent to about 6 mGy. A lifetime exposure to background radiation is about 250 mGy.
“The researchers found a 50% increase in risk per Gy of ionizing radiation (relative risk of 1.5), with evidence that the increase in risk per Gy is greater at lower doses – for 0 to 20 mGy there was a 130% increase in risk per Gy (relative risk of 2.3). While there are some limitations to the study it seems likely that these are reasonable estimates of the causal effects of ionizing radiation on cancer risk. Those limitations include issues with the accuracy of the instruments used to measure radiation doses in individuals which might result in a small under-estimation of the effect. Confounding by other risk factors is another limitation that might result in an over-estimation of the effects. (I am not sure that confounding really is much of a problem because: (a) any confounding factor would need to be correlated with the cumulative dose of radiation. Certain jobs within the nuclear industry may be associated with larger doses but I wouldn’t expect it to be a big effect and the association would need to be present in the different countries on which the study is based. (b) a confounder would need to be associated with a broad spectrum of cancers – alcohol and smoking are possibilities. (c) the confounding would need to be present after adjusting for socio-economic status indicated by job title. (d) there was no difference in effects after excluding the major smoking related cancer – lung cancer – and other smoking related cancers. Also no association between radiation and chronic obstructive pulmonary disease (which you would expect if smoking were a meaningful confounder). So confounding by smoking seems unlikely.)
“These increases per Gy seem large, but they need to be put in the context of the likely doses that the public might experience. One Gy is 10,000 chest Xrays or 150 CT scans of the chest. So, the relative increase in risk of solid cancers to an individual who has had 5 CT scans of the chest would be 2.5% and 0.2% for someone who has had 20 chest X-rays.
“Ionising radiation is clearly associated with an increased risk of cancer, but at the sorts of doses the general public are likely to be exposed to this increased risk is very small and not something to be concerned about. However, these results provide important data for organisations involved in setting guidelines and limits for radiation exposure in occupational settings.”
‘Cancer mortality after low dose exposure to ionising radiation in workers in France, the United Kingdom, and the United States (INWORKS): cohort study’ by David B Richardson et al. was published in the BMJ at 23:30 UK time on Wednesday 16 August 2023.
DOI: 10.1136/bmj‑2022‑074520
Declared interests
Society for Radiological Protection: “No conflicts of interest. The Society for Radiological Protection is the principal independent professional body for radiation protection in the UK. www.srp-uk.org.”
Prof Amy Berrington: “Professor Amy Berrington was not involved in the current study. She has worked with some of the authors to review the methodological issues and potential biases in low-dose radiation epidemiology studies (see Hauptmann,…, Berrington de Gonzalez JNCI Monograph 2020 https://pubmed.ncbi.nlm.nih.gov/32657347/).”
Mr Jim Thurston: “I declare that I have no conflicts of interest in making this statement.”
Matthew Dunn: “No conflicts of interest. Head of radiation physics for an NHS Trust.”
Dr Heather Williams: “I have no conflicts of interest.”
Prof Richard Wakeford: “I reviewed this paper for British Medical Journal, and my review comments will be publicly available at the BMJ website.
I am a member of the Technical Working Party of the UK Compensation Scheme for Radiation-Linked Diseases (http://www.csrld.org.uk), although the Scheme is unaware of my views on the INWORKS paper.”
Prof Jim Smith: “I did a small (< £5k) project for Japan Atomic Energy Agency about 10 years ago and had a NERC grant 2012-2017 which was part-funded by the Nuclear Decommissioning Authority. I don’t currently do consultancy work or have any nuclear industry links.”
Prof Paul Pharoah: “I have no conflicts of interest to declare.”