{"id":65175,"date":"2015-10-19T12:00:53","date_gmt":"2015-10-19T11:00:53","guid":{"rendered":"https:\/\/www.transcend.org\/tms\/?p=65175"},"modified":"2015-10-26T11:59:41","modified_gmt":"2015-10-26T11:59:41","slug":"radiation-and-cancer-risks-of-leukemia-in-nuclear-workers-more-than-double-previous-estimate","status":"publish","type":"post","link":"https:\/\/www.transcend.org\/tms\/2015\/10\/radiation-and-cancer-risks-of-leukemia-in-nuclear-workers-more-than-double-previous-estimate\/","title":{"rendered":"Radiation and Cancer: Risks of Leukemia in Nuclear Workers More Than Double Previous Estimate"},"content":{"rendered":"

\"nuclear<\/a><\/p>\n

16 Oct 2015 – <\/em>In 2013, I discussed<\/a> several epidemiological studies providing good evidence of radiogenic risks at very low exposure levels.<\/p>\n

A powerful new study<\/a> has been published in Lancet Haematology<\/em> which adds to this evidence. However the study\u2019s findings are more important than the previous studies, for several reasons.<\/p>\n

First, it provides \u201cstrong evidence\u201d<\/em>, as stated by the authors, of a \u201cdose-response relationship between cumulative, external, chronic, low-dose, exposures to radiation and leukemia\u201d<\/em>.<\/p>\n

Second, it finds radiogenic risks of leukemia among nuclear workers to be more than double the risk found in a previous similar study in 2005. The excess relative risk of leukemia mortality (excluding workers exposed to neutrons) was 4.19 per Gy.<\/p>\n

In 2005, a similar study<\/a> among nuclear workers (also excluding those exposed to neutrons) in 15 countries by several of the same authors found an ERR of 1\u00b793 per Sv. In other words, the new study\u2019s risk estimates are 117% higher than the older study. The clincher is that the new study\u2019s estimated risks are much more precise than before.<\/p>\n

Third, it confirms risks even at very low doses (mean = 1\u00b71 mGy per year). Unlike the Japanese bomb survivors\u2019 study, it observes risks at low dose rates rather than extrapolating them from high levels.<\/p>\n

Fourth, it finds risks do not depend on dose rate thus contradicting the ICRP\u2019s use of a Dose Rate Effectiveness Factor (DREF) which acts to reduce (by half) the ICRP\u2019s published radiation risks.<\/p>\n

Fifth, it finds radiogenic leukemia risks decline linearly with dose, contradicting earlier studies suggesting a lower, linear-quadratic relationship for leukemia. It strengthens the Linear No Threshold (LNT) model of radiogenic risks, as it now applies to leukemias as well as solid cancers.<\/p>\n

Sixth, the study finds no evidence of a threshold below which no effects are seen (apart from zero dose).<\/p>\n

Seventh, the study uses 90% confidence intervals and one-sided p-values. In the past, 95% intervals and two-sided p-values were often incorrectly used which had made it harder to establish statistical significance.<\/p>\n

Explanation for change<\/strong><\/p>\n

In an earlier version of this blog posted on 29th June 2015, I\u2019d written that the increase between the 2005 study and the present study was 50%, ie up from 1.93 to 2.96 per Gy. This was because the study\u2019s \u2018Discussion\u2019 section specifically compared these two studies and their risks, stating the older study\u2019s leukemia risk was smaller and less precise.<\/p>\n

However a detailed examination of the report reveals the following sentence in the para immediately before the Discussion section: \u201cWe assessed the effect of excluding people who had recorded neutron exposures; we showed a positive association for leukemia \u2026 (ERR per Gy 4\u00b719, 90% CI 1\u00b742-7\u00b780, 453 deaths)\u2026\u201d.<\/em><\/p>\n

To make sure readers get the point, the risk is greate<\/em>r when neutron exposed workers are excluded. This is important because the 2005 study excluded workers exposed to neutrons. Therefore the correct comparison is between the risks for non-neutron workers, that is between 4.19 and 1.93 per Gy \u2013 an increase of 117%, rather than 50%.<\/p>\n

I\u2019ve written to the report\u2019s authors about this but have not received any replies yet. I shall keep readers up-to-date on any progress.<\/p>\n

Study\u2019s credentials<\/strong><\/p>\n

The study\u2019s credentials are pretty impeccable. It\u2019s a huge study of over 300,000 nuclear workers adding up to over 8 million person years, thus ensuring its findings are statistically significant, ie with very low probability of occurring by chance.<\/p>\n

Also, it\u2019s an international study by 13 respected scientists from national health institutes in the US, UK, and France, as follows.<\/p>\n