INWORKS study does not provide evidence for increase in solid cancers from protracted exposure to low doses of ionising radiation
The publication by Richardson et al.(1) has attempted to answer the question: “Is protracted exposure to low doses of ionising radiation associated with an increased risk of solid cancer?” by studying the relationship between occupational radiation doses and solid cancers in workers who were employed in nuclear industry during the period 1944-2004 in France, UK, and USA. If occupational radiation doses were the predominant radiation doses of the workers, and other radiation doses were relatively unchanged during the period of the study, their use of occupational radiation dose as a surrogate for total radiation dose in the analysis would be justified. Let us examine if this is indeed true.
As indicated in the article by Thierry-Chef et al.,(2) during the early years of the employment (1950s to 1970s), the annual occupational doses of this cohort were relatively higher whereas in later years they were very low, with the mean occupational radiation dose of the cohort being ~21 mSv. The medical radiation dose the workers would have received, on the other hand, had an opposite time trend, because of the much higher use of diagnostic imaging during the later period compared to the earlier period of the study, assuming the workers had similar rates of diagnostic imaging as the general population. For example, the per capita medical radiation dose in USA was approximately 0.25 mSv in the 1960s (an estimate), 0.5 mSv in early 1980s,(3) and 3 mSv in 2006.(3) For the 12 year median employment period of the workers, the medical radiation doses would be ~3 mSv in the early years and ~21 mSv in the later years (using the average of data for the early 1980s and 2006). Not accounting for this large change in the medical radiation dose during the period of the study in comparison to the average occupational dose of 21 mSv is a major flaw in the design of the study, rendering the calculated dose-response relationships not trustworthy. Hence, this study does not provide any useful information on the association between prolonged radiation exposure and solid cancers, contrary to the study’s claim.
Several earlier studies of populations that had been subjected to prolonged radiation exposure have shown the cancer preventive effect of low-dose radiation. This includes (i) study of all cancers in Taiwan apartment residents who were exposed to radiation from contaminated building materials,(4) (ii) comparison of cancer mortality rates between radiation workers and non-radiation workers in US nuclear shipyards,(5) (iii) study of cancer mortality in male British radiologists who entered the field during 1955-79 in comparison to male general practitioners,(6) and (iv) study of cancer mortality rate in population evacuated from villages near Mayak nuclear weapons facility.(7) These population groups, which were subjected to cumulative average doses ranging from ~50 mSv to ~500 mSv over several years, showed significant reduction in cancers. The authors failed to refer to these comparable data and so presented a misleading picture of the current state of knowledge in this area.
In summary, this publication does not present any credible evidence for increase in solid cancers from protracted exposure to low doses of ionising radiation.
(1). Richardson DB, Cardis E, Daniels RD, Gillies M, O'Hagan JA, Hamra GB, et al. Risk of cancer from occupational exposure to ionising radiation: retrospective cohort study of workers in France, the United Kingdom, and the United States (INWORKS). BMJ 2015;351:h5359.
(2). Thierry-Chef I, Richardson DB, Daniels RD, Gillies M, Hamra GB, Haylock R, et al. Dose Estimation for a Study of Nuclear Workers in France, the United Kingdom and the United States of America: Methods for the International Nuclear Workers Study (INWORKS). Radiat Res 2015;183(6):632-42.
(3). NCRP. NCRP Report No. 160 - Ionizing Radiation Exposure of the Population of the United States (2009). Bethesda, Md.: National Council on Radiation Protection and Measurements, 2009.
(4). Hwang SL, Guo HR, Hsieh WA, Hwang JS, Lee SD, Tang JL, et al. Cancer risks in a population with prolonged low dose-rate gamma-radiation exposure in radiocontaminated buildings, 1983-2002. Int J Radiat Biol 2006;82(12):849-58.
(5). Sponsler R, Cameron JR. Nuclear shipyard worker study 1980 1988: a large cohort exposed to low-dose-rate gamma radiation. Int J of Low Radiat 2005;1(4):463-78.
(6). Berrington A, Darby SC, Weiss HA, Doll R. 100 years of observation on British radiologists: mortality from cancer and other causes 1897-1997. Br J Radiol 2001;74(882):507-19.
(7). Kostyuchenko VA, Krestinina L. Long-term irradiation effects in the population evacuated from the east-Urals radioactive trace area. Sci Total Environ 1994;142(1-2):119-25.
Mohan Doss, PhD, MCCPM
Fox Chase Cancer Center,
Philadelphia, PA 19111,
Competing interests: No competing interests