A relationship between radiation dose and thyroid nodules appears to exist in people who survived the atomic bombings at Hiroshima and Nagasaki as young children, new data published in JAMA Internal Medicine suggest.

Previous studies indicate that thyroid cancer risk may be higher among people exposed to radiation in childhood, but few have examined dose responses based on individual thyroid radiation dose in adults who were exposed as children. Further, little data exist on whether radiation affects development of small nodules, according to background information in the article.

To fill these gaps in knowledge, the researchers evaluated 3,087 people who survived the atomic bombings at Hiroshima and Nagasaki and were younger than 10 years at time of exposure. All were participants in the thyroid study of the Adult Health Study at the Radiation Effects Research Foundation.

Thyroid ultrasonography was conducted between 2007 and 2011, and fine-needle aspiration was performed on solid nodules.

Of all participants, data from 2,668 (mean age, 68.2 years; 1,213 men and 1,455 women) with known atomic bomb radiation doses (mean dose, 0.182 Gy) were included in the analysis.

A total of 470 participants had thyroid nodules sized greater than 10 mm in diameter. Of these, 16.0% were solid nodules, 1.8% were malignant tumors, 7.0% were benign nodules and 1.8% were cysts, with results revealing a significant association between these nodules and radiation dose.

Specifically, data showed that excess odds ratios (ORs) per gray unit were 1.65 (95% CI, 0.89-2.64) for all nodules, 1.72 (95% CI, 0.93-2.75) for solid nodules, 4.40 (95% CI, 1.75-9.97) for malignant tumors, 2.07 (95% CI, 1.16-3.39) for benign nodules and 1.11 (95% CI, 0.15-3.12) for cysts.

Dose effects also appeared to be greater with earlier childhood exposure, according to the researchers, with data indicating a significant interaction between age at exposure and dose for all nodules (P=.003) and solid nodules (P<.001).

However, radiation dose was not associated with small thyroid nodules, defined as less than 10 mm in diameter.

“The present study, conducted 62 to 66 years after the Hiroshima and Nagasaki atomic bombings, revealed that radiation effects on thyroid nodules exist in atomic bomb survivors exposed when they were younger than 10 years,” the researchers wrote.

“Radiation effects were significantly higher in those exposed at a younger age, but other significant modifiers were not identified.”

Reference

  1. Imaizumi M et al. JAMA Intern Med. 2014;doi:10.1001/jamainternmed.2014.6692.