Background The thyroid gland is one of the organs sensitive to ionizing radiation, and there are few studies on the effects of long-term exposure to low doses of ionizing radiation on the thyroid gland of radiation workers.

Objective To investigate thyroid abnormalities in workers in medical radiology departments in Guangdong Province and to identify potential influencing factors of thyroid abnormalities.

Methods A total of 1657 radiation workers from 48 hospitals in Guangdong Province were selected as survey subjects using convenience sampling, and their personal dose monitoring results and health examination information were retrospectively analyzed to determine the factors affecting thyroid abnormalities.

Results The M (P₂₅, P₇₅) of thyroid absorbed dose (D_T) was 1.55 (0.65, 3.96) mGy in the 1657 investigated workers. The attribute-specific medians of D_T were 1.29, 1.38, 1.99, and 3.51 mGy for departments of diagnostic radiology, interventional radiology, radiotherapy, and nuclear medicine, respectively; and 1.10, 1.55, and 1.80 mGy for job titles of nurse, technician, and physician, respectively. Differences in D_T by gender, age, years of radiological work, age of radiation exposure onset, occupational category, and job title were statistically significant (Z=−6.35, H=708.52, 918.20, 31.19, 95.64, 39.28, P<0.05). The positive rate of thyroid abnormalities in investigated workers was 46.53% (771/1657). Among them, the positive rate of abnormal thyroid function was 22.87% (379/1657), that of abnormal thyroid morphology was 33.98% (563/1657), and that of thyroid nodule was 26.55% (440/1657). The differences in thyroid abnormality rates by gender, age, years of radiation work, age of radiation exposure onset, D_T, and job title of radiation workers were statistically significant (χ²=51.89, 49.64, 20.54, 18.29, 12.07, 16.16, P<0.05). The differences in abnormal thyroid function positive rate by gender, age of radiation exposure onset, and job title were statistically significant (χ²=26.21, 6.21, 8.32, P<0.05). The differences in the positive rates of abnormal thyroid morphology and nodules were statistically significant by gender, age, years of radiological work, age of radiation exposure onset, D_T, and job title (abnormal thyroid morphology, χ²=40.24, 64.17, 37.63, 15.17, 19.28, 15.05; nodules, χ²=31.41, 77.98, 42.11, 19.16, 21.70, 13.52, P<0.05). The positive rates of thyroid abnormality, thyroid morphology abnormality, and nodules all showed a linear increasing trend with increasing age, years of radiation work, and age of radiation exposure onset (P<0.05). The results of logistic regression analysis indicated that the factors influencing thyroid abnormalities were female (OR=2.17, 95%CI: 1.72-2.74), increased years of radiological work (OR=1.04, 95%CI: 1.03-1.06), onset of radiation exposure in age groups of 30-34 and ≥35 years (OR=1.63, 95%CI: 1.12-2.37; OR=2.58, 95%CI: 1.74-3.29), and working in department of diagnostic radiology (OR=1.40, 95%CI: 1.07-1.84).

Conclusion Long-term exposure to low doses of ionizing radiation has an effect on thyroid abnormalities in medical radiation workers. Among them, being female, physicians, and working in department of diagnostic radiology are at a higher risk of abnormal thyroid function; being female, increased years of radiation work, and radiation exposure onset at age ≥30 years are associated with a higher risk of reporting abnormal thyroid morphology.