healthmedicinet

By Shreeya Nanda, Senior medwireNews Reporter

Results of the International Nuclear Workers Study (INWORKS) suggest a linear increase in incidence of solid cancers with increasing exposure to radiation.

“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”, the study authors write in The BMJ.

Personal monitoring data for occupational exposure to ionising radiation were obtained from company or government records for 308,297 nuclear industry workers in France, UK and the USA. Data on mortality were drawn from national and regional death registries, employer records and Social Security Administration records.

The majority (87%) of participants were male, and the mean cumulative dose to the colon for the 257,166 workers with a positive recorded dose was 20.9 mGy.

During a median follow-up of 26 years per worker, 19,748 of 66,632 total deaths were attributed to cancer, 17,957 of which were due to solid cancer. The risk of death from cancer increased by 51% per Gy of ionising radiation exposure, assuming a 10-year lag time between exposure and death. The risk of cancer mortality increased by 48% per Gy for all cancers excluding leukaemia, and by 47% for solid cancers.

When lung cancer cases were excluded to adjust for confounding by smoking, the results were similar to those for solid cancers, with a 46% increase in mortality per Gy of cumulative dose, report David Richardson (University of North Carolina, Chapel Hill, USA) and co-investigators.

However, the exclusion of all smoking-related malignancies (including oesophageal, liver, pancreatic and colorectal cancers, among others, which constituted 70% of solid cancers) gave an estimated excess relative rate of 37% per Gy.

Editorialist Mark Little (National Cancer Institute, Bethesda, Maryland, USA) says in a linked piece that this “suggests either heterogeneity of radiation risk by cancer site or some degree of confounding by smoking.”

He writes that the results of this “important study” were “[r]eassuringly […] not driven by results from any particular country, by contrast with the troubling heterogeneity by country present in the 15-Country analysis”, parts of which are updated in the current study.

However, the INWORKS study does have limitations, Little says, including the lack of information on smoking and occupational exposures to carcinogens such as asbestos, failure to account for dose uncertainty and the endpoint of all solid cancers, which include both highly radiogenic malignancies and those with considerably lower radiosensitivity.

In his opinion the “excess solid cancer risks associated with radiation in this cohort are modest”, but he adds that “it is equally clear that the excess risks are unlikely to be zero.”

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