Diagnostic radiography exposure increases the risk for thyroid microcarcinoma

Abstract

Objective Thyroid cancer incidence and diagnostic x-ray exposures, particularly CT scans and nuclear medicine examinations have increased substantially in the United States. However, very few epidemiologic studies have directly investigated their associations. Methods A population-based case-control study was conducted in Connecticut in 2010–2011 including 462 histologically confirmed incident thyroid cancer cases and 498 population-based controls. Multivariate unconditional logistic regression models were used to estimate the associations between diagnostic x-rays and risk of thyroid cancer controlling for potential confounding factors. Results Exposure to any diagnostic x-rays was associated with an increased risk of well-differentiated thyroid microcarcinoma (tumor size ≤10 mm, OR=2.76, 95%CI: 1.31–5.81). The highest risk increase occurred with nuclear medicine examinations (excluding cardiology tests and thyroid uptake studies; OR=5.47, 95%CI: 2.10–14.23), followed by chest CT scans (OR=4.30, 95%CI: 1.66–11.14), head and neck CT scans (OR=3.88, 95%CI: 1.75–8.63), upper gastrointestinal series (OR=3.56, 95%CI: 1.54–8.21), lower gastrointestinal series (OR=3.29, 95%CI: 1.41–7.66), kidney x-rays involving dye injection into a vein or artery (OR=3.21, 95%CI: 1.20–8.54), mammograms (OR=2.95, 95%CI: 1.14–7.61), chest x-rays (OR=2.93, 95%CI: 1.37–6.29), and abdomen CT scans (OR=2.54, 95%CI: 1.02–6.30). No significant associations were found between these imaging modalities and thyroid tumors larger than 10 mm. Conclusions This study provides the first direct evidence that CT scans and nuclear medicine examinations are associated with an increased risk of thyroid cancer. The novel finding that an array of diagnostic x-ray procedures are associated thyroid microcarcinomas warrants further investigation.

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