Objective  To analyze the trends in the frequency and dose of ¹³¹I therapy for differentiated thyroid carcinoma (DTC) patients without distant metastases following thyroidectomy, based on guidelines and consensus.

Methods  A retrospective cohort study was conducted to collect medical records of 1 289 DTC patients without distant metastases who received ¹³¹I therapy at the First Hospital of Shanxi Medical University from 2018 to 2022. The patients consisted of 387 males and 902 females, with a median age of 44 years and an age range of 18–85 years. Statistics and analysis were conducted on the patients′ basic information, frequency of ¹³¹I therapy, initial ¹³¹I therapy dose, and treatment efficacy. The chi-square test was used for inter-group comparison of count data. With reference to the 2019 Expert Consensus on Postoperative ¹³¹I Pre-therapy Evaluation of Differentiated Thyroid Cancer (hereinafter referred to as the 2019 Consensus) and the 2021 Guidelines for Radioiodine Therapy of Differentiated Thyroid Cancer (2021 Edition) (hereinafter referred to as the 2021 Guidelines), linear trend chi-square test was performed to analyze the linear trend of patients′ ¹³¹I therapy frequency and initial ¹³¹I therapy dose distribution across different years. Spearman correlation analysis was used to assess the correlation between year and patients′ ¹³¹I therapy frequency and initial ¹³¹I therapy dose distribution.

Results  In different years from 2018 to 2022, the proportions of DTC patients without distant metastases who received only one ¹³¹I therapy were 5.99% (10/167), 34.69% (94/271), 80.98% (132/163), 92.79% (309/333), and 94.08% (334/355), respectively. According to the 2019 Consensus, the proportion of patients who received only one ¹³¹I therapy in 2020 was significantly higher than that in 2019 (χ²=87.407, P<0.001) and then gradually stabilized. Linear trend chi-square test revealed a linear trend in the frequency of ¹³¹I therapy among patients in different years (χ²_trend=576.856, P_trend<0.001). Spearman correlation analysis revealed a negative correlation between the year and the frequency of ¹³¹I therapy among patients (r=−0.642, P<0.001). In different years from 2018 to 2022, the proportions of patients who received their initial ¹³¹I therapy at a dose of 3.70 GBq were 93.41% (156/167), 95.20% (258/271), 80.98% (132/163), 76.28% (254/333), and 50.42% (179/355), respectively. The proportions of patients who received their initial ¹³¹I therapy at a dose of >3.70 GBq and ≤5.55 GBq were 0.60% (1/167), 2.58% (7/271), 17.79% (29/163), 23.42% (78/333), and 49.01% (174/355), respectively. According to the 2021 Guidelines, there was a significant difference in the distribution of patients′ initial ¹³¹I therapy doses between 2021 and 2022 (χ²=49.242, P<0.001). Linear trend chi-square test revealed a linear trend in the distribution of doses for patients′ initial ¹³¹I therapy across different years (χ²_trend=239.731, P_trend<0.001). Spearman correlation analysis revealed a positive correlation between the year and the distribution of initial ¹³¹I therapy doses administered to patients (r=0.441, P<0.001). There was no statistically significant difference in the efficacy of ¹³¹I therapy among patients in different years from 2018 to 2022 (χ²=1.031, P=0.905).

Conclusions  Guided by the 2019 Consensus, the proportion of DTC patients without distant metastases who received only one ¹³¹I therapy after thyroidectomy has been increasing year by year in 2020 and beyond. Under the guidance of the 2021 Guidelines, the proportion of patients who received their initial ¹³¹I therapy at a dose of >3.70 GBq and ≤5.55 GBq increased slightly in 2022, and the treatment efficacy was satisfactory.