Objective To investigate the changes in ambient dose equivalent rate and its influencing factors in patients with hyperthyroidism after ¹³¹I treatment to provide a theoretical basis for radiation protection.

Methods The clinical data of 42 patients with hyperthyroidism who received ¹³¹I treatment in the First Affiliated Hospital of Chongqing Medical University from October 2018 to November 2019 were retrospectively analyzed. The patients included 12 males and 30 females aged 14–68 (38.7±11.9) years old. The ambient dose equivalent rates at 0, 0.3, 1.0, 2.0 and 4.0 m from the front of the neck of the patient were measured at 2 and 4 weeks after ¹³¹I treatment, and their trends were analyzed. The correlations among the gender, age, thyroid iodine uptake rate, effective half-life of ¹³¹I , medication dose, and ambient dose equivalent rate of the patients were also investigated. The measurement data were compared between the two groups via independent samples t test, and the correlation between the ambient dose equivalent rate and each index was analyzed through Pearson correlation analysis.

Results The ambient dose equivalence rate decreased gradually with the increase in the measurement distance at 2 and 4 weeks after ¹³¹I treatment. At 2 weeks after ¹³¹I treatment and distance ≥ 2.0 m from the patients, the ambient dose equivalent rates were all <25 μSv/h. At 4 weeks after ¹³¹I treatment and distance ≥ 0.3 m from the patients, the ambient dose equivalent rates were all <25 μSv/h. There was no significant difference in the ambient dose equivalent rates at different measurement distances in patients of different genders (t=−0.467–1.766, all P>0.05). At 2 weeks after ¹³¹I treatment, the ambient dose equivalent rates measured at distances of 0, 0.3, and 4.0 m were positively correlated with the effective half-life of ¹³¹I (r=0.318–0.487, all P<0.05); the ambient dose equivalent rates measured at distances of 2.0 and 4.0 m were positively correlated with the medication dose (r=0.546, 0.491; both P<0.01); the ambient dose equivalent rates at different measurement distances had no correlation with the patients' age and thyroid iodine uptake rate (r=−1.158–0.162, all P>0.05). At 4 weeks after ¹³¹I treatment, the ambient dose equivalent rates measured at distances of 0, 0.3, 1.0 and 2.0 m were positively correlated with the effective half-life of ¹³¹I (r=0.319–0.380, all P<0.05); the ambient dose equivalent rate measured at distances of 0 m was positively correlated with the patients' age (r=0.429, P<0.01); the ambient dose equivalent rate measured at distances of 2.0 m was positively correlated with the thyroid iodine uptake rate (r=0.353, P<0.05); the ambient dose equivalent rates at different measurement distances had no correlation with the medication dose (r=0.020–0.157, all P>0.05).

Conclusions Patients with hyperthyroidism should try to avoid close contact with their family members within 4 weeks after ¹³¹I treatment. Clinicians should provide guidance on radiation protection during the home isolation of patients with hyperthyroidism on the basis of the measurement results of the ambient dose equivalent rate and the effective half-life of ¹³¹I in the patients' body.