Objective To explore the dynamic change of the ambient dose equivalent rate during diagnostic whole-bady scan with differentiated thyroid carcinoma after ¹³¹I therapy 6 months.

Methods This study enrolled 85 patients aged (18 males and 67 females; 43.9±12.0 years old ) with DTC who received ¹³¹I therapy in the Department of Nuclear Medicine of The First Affiliated Hospital of Zhengzhou University from August 2018 to January 2019. Among them, 18 patients were ≥55 years old and 67 patients were <55 years old. All patients were given 148 MBq (4 mCi) of ¹³¹I on an empty stomach and received diagnostic whole-body scan 2 days later. The negative group (n=48) was defined as the excellent response. The patients in this group were administered with thyroid-stimulating hormone-stimulated thyroglobulin (<1 μg/L) in the absence of structural or functional evidence of disease (and in the absence of anti-Tg antibodies). The positive group (n=37) was defined as the biochemically incomplete response, structurally incomplete response, and indeterminate response. Ambient dose equivalent rate was determined l m away from the patients at 2, 24, and 48 h after ¹³¹I administration. One-way repeated measures ANOVA was used on the three patient groups. T test was used to compare the ambient dose equivalent rate at 1 m between different groups of gender, age, and treatment effects.

Results The range of ambient dose equivalent rate at 1 m at 2, 24, and 48 h was (6.55±1.42), (1.92±0.65), and (0.58±0.22) μSv/h, respectively, indicating that ambient dose equivalent rate decreased over time. The differences were statistically significant (F=807.30, P=0.000). No statistically significant difference was found in ambient dose equivalent rate at 1 m after ¹³¹I administration at any time in groups of different genders. The ambient dose equivalent rate at 1 m at 24 h was higher in the ≥55 age group than in the <55 age group (t=2.29, P=0.02), and the other two time points were not statistically significant. No statistically significant difference was found between the negative group and the positive group at each time point.

Conclusions The ambient dose equivalent rate of patients with DTC after ¹³¹I treatment who received the diagnostic dose of ¹³¹I for 48 h was less than 1.40 μSv/h (the 2017 clinical nuclear medicine patient protection requirements, WS 533-2017). Thus, no restrictions for the patients to travel should be imposed as they do not exert harmful radiation on others.