Thyroid diseases in Hiroshima and Nagasaki atomic-bomb survivors (Renewal of RP2-99)

Summary

The Life Span Study (LSS) demonstrated that thyroid cancer risk increased among A-bomb survivors who were exposed at less than 20 years of age, even 50 years after their radiation exposure. Regarding noncancer thyroid diseases among survivors, risk of benign nodules increased in the AHS thyroid studies, whereas risks of thyroid dysfunction and autoimmune thyroid diseases have been inconsistent. However, previous analyses are all cross-sectional; a longitudinal analysis has not been conducted. Furthermore, the influence on thyroid disorders of radiation exposure in utero has not been fully evaluated because of concern about limited power.

Recently, thyroid nodules are frequently detected in adults with the use of imaging procedures in clinical practice. It is generally recommended that thyroid nodules be followed by periodical examination. However, there is no consensus about methods or duration of follow-up in the existing guidelines. This is because data on the long-term natural prognosis of thyroid nodules and the associated effects of radiation are insufficient.

The aims of this study are 1) to clarify associations between A-bomb radiation exposure and incidence of thyroid disorders among survivors exposed at younger ages and in utero, and 2) to clarify A-bomb radiation effects on progression of thyroid nodules. This study is intended to clarify the effects of radiation exposure at younger ages on thyroid diseases in the elderly. Furthermore, by elucidating the natural history of thyroid nodules and associated radiation effects, the study will contribute towards creating guidelines for the follow-up of thyroid nodules detected among radiation-exposed persons.