Risk of Thyroid Nodules in Residents of Belarus Exposed to Chernobyl Fallout as Children and Adolescents

Abstract

Context: Although radiation exposure is an important predictor of thyroid cancer on diagnosis of a thyroid nodule, the relationship between childhood radiation exposure and thyroid nodules has not been comprehensively evaluated.

Objective: To examine the association between internal I-131 thyroid dose and thyroid nodules in young adults exposed during childhood.

Design, setting, and participants: In this cross-sectional study, we screened residents of Belarus aged ≤18 years at the time of the Chernobyl nuclear accident for thyroid disease (median age, 21 years) with thyroid palpation, ultrasonography, blood/urine analysis, and medical follow-up when appropriate. Eligible participants (N = 11,421) had intact thyroid glands and doses based on direct individual thyroid activity measurements.

Main outcome measures: Excess odds ratios per Gray (EOR/Gy, scaled at age 5 years at exposure) for any thyroid nodule and for nodules grouped by cytology/histology, diameter size, and singularity.

Results: Risk of any thyroid nodule increased significantly with I-131 dose and, for a given dose, with younger age at exposure. The EOR/Gy (95% confidence intervals) for neoplastic nodules (3.82; 0.87 to 15.52) was significantly higher than for nonneoplastic nodules (0.32; <0.03 to 0.70) and did not vary by size; whereas the EOR/Gy for nonneoplastic nodules did vary by size (P = 0.02) and was 1.55 (0.36 to 5.46) for nodules ≥10 mm and 0.02 (<-0.02 to 0.70) for nodules <10 mm. EORs/Gy for single and multiple nodules were comparable.

Conclusions: Childhood exposure to internal I-131 is associated with increased risk of neoplastic thyroid nodules of any size and nonneoplastic nodules ≥10 mm.

Figure 1.

Radiation-related odds ratios and 95% CIs for thyroid nodules in Belarus. (a) Black line represents fitted dose-response relationship, and points represent categorical results with 95% CIs. (b) Black line and points represent neoplastic nodules, and gray line and points represent nonneoplastic nodules. (c) Black line and points represent large (≥10 mm) nodules, and gray line and points represent small (<10 mm) nodules. (d) Black line and points represent multiple nodules, and gray line and points represent single nodules. Models were adjusted for sex, log age at screening, urban status at screening, oblast of residence at screening (Minsk, Gomel, other), diffuse goiter detected at screening, and self-reported family history of thyroid disease and are scaled for a person 5 years old at time of exposure. Results are restricted to participants exposed to <5 Gy. The odds ratio is equivalent to the excess odds ratio plus one (OR = EOR + 1). The EOR is the vertical distance between the observed/fitted values and the dashed line.

Figure 2.

Radiation-related excess odds ratios and 95% CIs for thyroid nodules in Belarus. *Models were adjusted for sex, log age at screening, urban status at screening, oblast of residence at screening (Minsk, Gomel, other), diffuse goiter detected at screening, and any family history of thyroid disease and are scaled for participants 5 years old at time of exposure. P values based on likelihood ratio tests with models adjusted for all factors described above and an age at time of accident interaction term are shown. Results are restricted to participants exposed to <5 Gy. ^†Among small nodules, P = 0.023 for test of difference in dose-response between nonneoplastic and neoplastic nodules. Among large nodules, P = 0.381 for test of difference in dose-response between nonneoplastic and neoplastic nodules. ^‡Sex-specific EORs for multiple nodules are 0.10 (95% CI, <−0.17 to 0.93) in men and 1.44 (95% CI, <−0.46 to 3.68) in women.

Figure 3.

Radiation-related odds ratios and 95% CIs for thyroid nodules by age at time of Chernobyl accident in Belarus. (a) Black line represents fitted dose-response realtionship; points represent categorical results with 95% CIs (dose-response P < 0.001). (b) Black line and points represent neoplastic nodules (dose-response P = 0.002), and gray line and points represent nonneoplastic nodules (dose-response P = 0.016). (c) Black line and points represent large (≥10 mm) nodules (dose-response P < 0.001), and gray line and points represent small (<10 mm) nodules (dose-response P = 0.002). (d) Black line and points represents multiple nodules (dose-response P = 0.001), and gray line and points represent single nodules (dose-response P < 0.001). Models were adjusted for sex, log age at screening, urban status at screening, oblast of residence at screening (Minsk, Gomel, other), diffuse goiter detected at screening, and self-reported family history of thyroid disease. Nonparametric point estimates use cut-offs of 5 and 10 years old. Results are restricted to participants exposed to <5 Gy. P values are based on likelihood ratio tests for the inclusion of an age at time of accident interaction term (coded continuously, 1 degree of freedom). The odds ratio is equivalent to the excess odds ratio plus one (OR = EOR + 1). The EOR is the vertical distance between the observed/fitted values and the dashed line.