Objective To analyze the value of SPECT/CT and iodine uptake rate in predicting response to the first ¹³¹I treatment of patients with differentiated thyroid carcinoma (DTC).

Methods From January 2021 to January 2022, 138 postoperative patients with DTC who received ¹³¹I treatment for the first time in Suizhou Hospital, Hubei University of Medicine were retrospectively analyzed, including 36 males and 102 females aged (47.8±9.8) years. All patients underwent ¹³¹I whole-body scan and SPECT/CT imaging, determine the iodine uptake rate. After ¹³¹I treatment, the patients were followed up for at least 6 months to evaluate efficacy and response. The patients were divided into the excellent response (ER) group and non-ER group. Comparison of clinical data between the two groups select independent sample t-test, Mann Whitney U test, χ² conduct analysis, and Logistic regression analysis were used to identify the predictors of the unsatisfactory response to the first ¹³¹I therapy in patients with DTC. In addition, the receiver operating characteristic (ROC) curve was used to obtain the best critical value, and the area under curve (AUC) was used to determine the predictive value of predictive factors on treatment response.

Results The proportion of extraglandular invasion (63.89% vs. 36.27%); the proportion of tumor, node, metastasis (TNM) stages Ⅲ–Ⅳ (69.44% vs. 44.12%); the proportion of recurrence risk stratification medium/high risk (91.67% vs. 68.63%); preablation stimulated thyroglobulin (psTg) level before treatment (1.65 (0.90, 1.87) μg/L vs. 1.32 (0.65, 1.66) μg/L); and lymph node short diameter in the non-ER group ((6.33±2.01) mm vs. (4.52±1.43) mm) were higher than those in the ER group, and the thyroid-stimulating hormone (TSH) level (59.10 (35.32, 118.33) mU/L vs. 65.33 (42.41, 120.33) mU/L), and iodine uptake rate before treatment ((5.63±1.50)% vs. (8.65±2.33)%) were lower than those in the ER group, with statistically significant differences (t=5.314, 5.837; χ²=6.829–8.257; Z=4.683, 6.861; all P<0.05). Multivariate Logistic regression analysis showed the following predictive factors of the unsatisfactory response to the first ¹³¹I treatment after DTC operation: the level of TSH before treatment, the proportion of extraglandular invasion, the proportion of TNM stages Ⅲ–Ⅳ, the proportion of middle/high risk of recurrence risk stratification, the level of psTg, the short diameter of lymph nodes, and the iodine uptake rate (OR=1.941–4.545, all P<0.01). The ROC curve analysis results showed that the critical value of the maximum Yodon index of the short diameter of lymph nodes displayed by SPECT/CT was 5.52 mm, and the AUC that predicted the unsatisfactory response to the first ¹³¹I treatment of DTC was 0.766 (95%CI: 0.687–0.834). The critical value corresponding to the maximum Yodon index of the iodine uptake rate was 7.47%, with an AUC of 0.749 (95%CI: 0.669–0.819), and the AUC of the combination of the two is 0.911 (95%CI: 0.850–0.953). The AUC predicted by the two methods for the first ¹³¹I treatment response of DTC was higher than that predicted by the two methods alone, and the difference was statistically significant (P<0.001).

Conclusion The short diameter of lymph nodes of SPECT/CT imaging and the iodine uptake rate are considered as predictors of dissatisfaction with the first ¹³¹I treatment effect to DTC, and such predictors are of great importance in predicting the response of ¹³¹I treatment. Furthermore, the combination of the two methods has a better predictive value.