Risk of Thyroid Cancer among Chernobyl Liquidators

Abstract

After the Chernobyl accident in 1986, the "liquidators" or clean-up workers were among those who received the highest radiation doses to the thyroid from external radiation. Some were also exposed to radioiodines through inhalation or ingestion. A collaborative case-control study nested within cohorts of Belarusian, Russian and Baltic liquidators was conducted to evaluate the radiation-induced risk of thyroid cancer. The study included 107 cases and 423 controls. Individual doses to the thyroid from external radiation and from iodine-131 ((131)I) were estimated for each subject. Most subjects received low doses (median 69 mGy). A statistically significant dose-response relationship was found with total thyroid dose. The Excess Relative Risk (ERR) per 100 mGy was 0.38 [95% confidence interval (CI): 0.10, 1.09]. The risk estimates were similar when doses from (131)I and external radiation were considered separately, although for external radiation the ERR was not statistically significantly elevated. The ERR was similar for micro carcinomas and larger size tumors, and for tumors with and without lymph node involvement. Although recall bias and uncertainties in doses could have affected the magnitude of the risk estimates, the findings of this study contribute to a better characterization the risk of thyroid cancer after radiation exposure in adulthood.

Author response to “Re: occupation and thyroid cancer.”

“…We appreciate his interest in our review and his identification of these missing papers. The Muirhead et al 3 and Kesminiene et al 4 publications were eligible for inclusion in our review. Although the search engine we used to identify articles had the ability to search all text in a document and not just the abstract, it is likely that we missed the Muirhead article as the data on thyroid cancer incidence was presented in the supplementary material and not the main text.…”

“…Although the search engine we used to identify articles had the ability to search all text in a document and not just the abstract, it is likely that we missed the Muirhead article as the data on thyroid cancer incidence was presented in the supplementary material and not the main text. Kesminiene et al 4 were published after we initiated our review, and within our inclusion cut-off time period, but the article was unfortunately missed during our follow-up search prior to publication. The Rahu et al 5 article was published in September 2013, just after our inclusion cut-off of August 2013, and was thus ineligible for our review.…”

“…In a large cohort of UK radiation workers, Muirhead et al 3 observed a positive trend in incidence with radiation dose for thyroid cancer (p=0.079) that approached statistical significance based on a one-sided test (supplementary table 4). The two recent studies of thyroid cancer risk in Chernobyl ‘liquidators’, or clean-up workers, were undertaken on workers who were among those who received the highest radiation doses from external radiation at Chernobyl 4 5. In the nested case-control study of the Belarusian, Russian and Baltic liquidators, the investigators reported a statistically significant dose-response trend with total thyroid radiation dose (excess relative risk, ERR, per 100 mGy=0.38 (0.10–1.09)) 4.…”

“…The two recent studies of thyroid cancer risk in Chernobyl ‘liquidators’, or clean-up workers, were undertaken on workers who were among those who received the highest radiation doses from external radiation at Chernobyl 4 5. In the nested case-control study of the Belarusian, Russian and Baltic liquidators, the investigators reported a statistically significant dose-response trend with total thyroid radiation dose (excess relative risk, ERR, per 100 mGy=0.38 (0.10–1.09)) 4. Interestingly, they also found that the ERR was similar for microcarcinomas and larger size tumours and for tumours with and without lymph node involvement.…”

Re: Occupation and thyroid cancer

“…Neither a study of cancer incidence in a large cohort of UK radiation workers2 nor some recent studies of thyroid cancer incidence among Chernobyl clean-up workers3 4 were included in the review,1 despite being available online prior to the cut-off date of August 2013.…”