Thyroid Neoplasia, Autoimmune Thyroiditis, and Hypothyroidism in Persons Exposed to Iodine 131 From the Hanford Nuclear Site

Abstract

Context Approximately 740000 Ci (2.73 ϫ 10 16 Bq) of iodine 131 (131 I) were released to the atmosphere from the Hanford Nuclear Site in Washington State from 1944 through 1957. The risk of thyroid disease resulting from prolonged environmental 131 I exposure is poorly understood. Objective The Hanford Thyroid Disease Study (HTDS) was conducted to determine if thyroid disease is increased among persons exposed as children to atmospheric releases of 131 I from Hanford. Design Retrospective cohort study. Exposure could have occurred from December 1944 through 1957. Follow-up occurred until the time of the HTDS examination (December 1992-September 1997). Participants' thyroid radiation doses from Hanford's 131 I releases were estimated from interview data regarding residence and dietary histories. Setting The cohort included a sample of all births from 1940 through 1946 to mothers with usual residence in 1 of 7 counties in eastern Washington State. Participants Of 5199 individuals identified, 4350 were located alive and 3440 were evaluable; ie, had sufficient data for dose estimation and received an HTDS evaluation for thyroid disease, including a thyroid ultrasound, physical examination, and fine needle biopsy if required to evaluate thyroid nodularity. Main Outcome Measures Thyroid cancer, benign thyroid nodules, total neoplasia, any thyroid nodules, autoimmune thyroiditis, and hypothyroidism. Results There was no evidence of a relationship between Hanford radiation dose and the cumulative incidence of any of the outcomes. These results remained unchanged after taking into account several factors that might confound the relationship between radiation dose and the outcomes of interest. Conclusion These results do not support the hypothesis that exposure during infancy and childhood to 131 I at the dose levels (median, 97 mGy; mean, 174 mGy) and exposure circumstances experienced by our study participants increases the risk of the forms of thyroid disease evaluated in this study.

A Cohort Study of Thyroid Cancer and Other Thyroid Diseases after the Chornobyl Accident: Dose-Response Analysis of Thyroid Follicular Adenomas Detected during First Screening in Ukraine (1998-2000)

“…This is lower than an excess relative risk of 13.0 per gray (95 percent CI: 2.7, 68.7; n ¼ 20) from the Nevada test site study (29) and much higher than 0.1 per gray (95 percent CI: <À0.3, 2.2; n ¼ 33) from the Hanford Thyroid Disease Study (27). Davis et al (27) have suggested that some of the differences in estimates lie in the different composition of the radionuclides in the fallout: While the Hanford Thyroid Disease Study thyroid dose was mostly due to 131 I, other radionuclides as well as external ionizing radiation exposures had greater contribution in the doses analyzed in the Nevada test site study. Hoffman et al (43) suggested that high uncertainties in dose reconstructions in the Hanford Thyroid Disease Study may account for negative findings.…”

“…However, no thyroid doses were available for analysis. The other two, one investigating the effects of the fallout after nuclear weapons testing at the Nevada test site (29) and the other (the Hanford Thyroid Disease Study) (27) investigating the effects of atmospheric releases, relied on dose reconstructions based on residential history years after exposures had occurred, and they were based on small numbers of cases of ''thyroid neoplasia.'' Our risk estimate for ''thyroid neoplasia'' was 4.39 per gray (95 percent CI: 1.67, 13.28; n ¼ 58 cases).…”

“…An exception is the study by Hall et al (26) that showed a significant doseresponse relation between diagnostic administration of 131 I and thyroid nodularity among women. The results of the studies investigating the effects of exposures to environmental radioactive iodines on benign thyroid tumors have been contradictory, ranging from no effect (27) to an effect comparable in magnitude with that for external irradiation (28,29).…”

Ultrasound-Detected Thyroid Nodule Prevalence and Radiation Dose from Fallout

“…(2) Most medical exposures to 131 I have occurred in adults, who are relatively insensitive to radiationrelated thyroid carcinogenesis based on data from populations exposed to external radiation (4). (3) Environmental exposures of children to radioiodines have occurred, notably from the 1986 reactor accident at Chernobyl (7), atmospheric releases from the Hanford Nuclear Site in Washington state (43)(44)(45), and fallout from nuclear tests in the Marshall Islands in the Central Pacific (46), the Nevada Test Site in the U.S. (3,(47)(48)(49), as well as the SNTS (11,25). However, studying such exposed populations can pose enormous problems in individual dose reconstruction and case identification.…”

Increasing world incidence of thyroid cancer: Increased detection or higher radiation exposure?

“…35,36 On the other hand, smaller amounts of radiation exposure, i.e. from either lower dosage of fallout 37 or from diagnostic use of radioisotopes, have not been associated with a higher incidence of thyroid cancer. Thus, diagnostic 131-Iodine was not associated with thyroid neoplasia in a total of over 6000 children 38,39 or in another review of 2727 patients who received 131-Iodine therapy for hyperthyroidism.…”