1. In a cohort of patients who were younger than 10 years of age at the time of radiation exposure at Hiroshima or Nagasaki, there was a significantly increased risk of malignant and benign thyroid nodules more than 10 mm in diameter.
2. There was a significant association between prevalence of thyroid nodules and the age at exposure, as well as radiation dose, suggesting dose effects were higher for earlier childhood exposure.
Evidence Rating Level: 2 (Good)
Study Rundown: Thyroid cancer has been associated with ionizing radiation exposure in early childhood. In a prospective study of survivors of the Chernobyl nuclear reactor incident, exposed survivors had a higher risk of thyroid cancer. Although previous studies have examined the use of thyroid ultrasound in detecting nodules in radiation-exposed populations, there has been little investigation into the dose response. This study aimed to investigate thyroid disease in atomic bomb radiation exposed patients from Hiroshima and Nagasaki, 62 to 66 years after exposure, as well as to investigate radiation dose-response relationships in this population.
The study authors found a significant risk association with atomic bomb radiation exposure and malignant and benign nodules more than 10 mm in diameter. There was a significant association between prevalence of thyroid nodules and the age at exposure as well as radiation dose, suggesting dose effects were higher for earlier childhood exposure. There was no dose response relationship found for thyroid nodules small nodules (< 10 mm in diameter). One limitation of the study is the retrospective nature of the study. Strengths include the large number of patients included, as well as the availability of dosimetry estimation of thyroid radiation dose exposure.
In-Depth [retrospective cohort]: This study included 3087 Hiroshima and Nagasaki bomb survivors who were younger than 10 years at the time of exposure, who also participated in the thyroid study of the Adult Health Study. 2688 participants with known atomic bomb thyroid radiation doses were analyzed from October 2007 to 2011. All participants had thyroid ultrasound, and those with nodules more than 10 mm in diameter were referred to have fine-needle aspiration biopsy and cytology. The primary outcome was the prevalence of all thyroid nodules with 10 mm or more diameter, including solid nodules and cysts, prevalence of small thyroid nodules less than 10 mm in diameter detected by ultrasound.
470 patients had thyroid nodules of diameter 10 mm or more (17.6%). 16% of survey participants had solid nodules, with 1.8% with malignant tumors, and 7% with benign nodules, and 1.8% with cysts. The excess odds ratio per gray unit was 1.65 (95% CI 0.89-2.64) for all nodules, 4.40 (95% CI 1.75-9.97) for malignant tumors, and 2.07 (95% CI 1.16-3.39) for benign tumors. The age at exposure and the dose was significantly associated with prevalence of all nodules (P=0.003) and solid nodules (P<0.001). There was not a significant dose-response relationship for nodules less than 10 mm.
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