To investigate the response to ¹³¹I therapy and to explore the influence factors in postoperative differentiated thyroid carcinoma (DTC) patients with negative preablative stimulated thyroglobulin (psTg) and iodine-positive lymph node after the first radioablation.

From May 2016 to October 2018, 108 DTC patients (28 males, 80 females, age: (45.7±10.4) years) with negative psTg who underwent ¹³¹I treatment for the first time in the Affiliated Hospital of Qingdao University were retrospectively enrolled. All patients had iodine-positive lymph nodes, which were showed by SPECT/CT imaging 5-6 d after ¹³¹I treatment. The treatment response was evaluated at 6-24 month after ¹³¹I treatment. Patients were divided into excellent response (ER) group and non-excellent response (non-ER) group according to the response to the first ¹³¹I treatment. Independent-sample t test, χ² test and Mann-Whitney U test were used to analyze differences of factors (e.g. age, gender, extraglandular infiltration) between the 2 groups, and then multivariate logistic regression was performed to find the influence factors for treatment response. The receiver operating characteristic (ROC) curve was employed to evaluate the predictive value of the iodine-positive lymph node size in ¹³¹I treatment response.

A total of 82 patients (75.93%, 82/108) achieved ER, and 26 (24.07%, 26/108) was non-ER patients. There were significant differences in age (t=-2.540, P=0.016), extraglandular infiltration (χ²=5.764, P=0.016), T stage (χ²=19.857, P<0.001), N stage (χ²=14.145, P=0.001), risk stratification of recurrence (χ²=11.487, P=0.003), ultrasound results before ¹³¹I treatment (χ²=44.819, P<0.001), dose of the first¹³¹I treatment (U=780.0, P=0.018), size (long diameter) of iodine-positive lymph node (U=184.0, P<0.001), and psTg level (U=776.0, P=0.037) between ER and non-ER groups. Multivariate logistic regression showed that age, size of iodine-positive lymph node and ultrasound results before ¹³¹I treatment were closely related to ¹³¹I treatment response. The odds ratio (OR) values (95% CI) were 1.123 (1.025-1.231), 4.275 (1.893-9.653) and 260.86 (8.123-8 376.764), respectively. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value for non-ER were 100%(26/26), 70.73%(58/82), 77.78%(84/108), 52.00%(26/50) and 100%(58/58) respectively when the cut-off value of iodine-positive lymph node size was 5.5 mm.

The response of some DTC patients with negative psTg and iodine-positive lymph node after the first radioablation were non-ER. Age, ultrasound results before ¹³¹I treatment and size of iodine-positive lymph node are sensitive indicators for predicting clinical outcome in DTC patients with negative psTg and iodine-positive lymph node after the first radioablation.

Thyroid neoplasms; Radiotherapy; Iodine radioisotopes; Thyroglobulin