Abstract
1517
Introduction: For 131I-avid metastases, it always recommend 6-12 months interval for repeated radioiodine therapy (RAI). However, it’s not clear that how to choose the proper interval and the results if we prolong the interval more than 12 months, so in this study, we respectively compare RAI efficiency and side effects on different RAI interval for DTC patients with pulmonary metastases.
Methods: Collecting data of DTC patients with pulmonary metastasis who undertook at least three RAI from 2012 to 2018 in our department. Surveillance suppressed thyroglobulin(Tg) every 3-6 months during RAI interval, if the Tg level of post-RAI decreased first and then at least kept stable when compared with tg level before the lasted treatment, the interval was prolonged to 12 or more than 12 months. Patients with bone metastasis and positive Tg antibody (serum TgAb>40IU/ml) were excluded. Recording the stimulated serum Tg, tumor number and size on computer tomography (CT), salivary function and blood test results of each RAI. Included patients were categorized into three groups based on the time to lasted RAI: 1) Group 1: less than six months, 2) Group 2: six to twelve months, and 3) Group 3: more than twelve months. In subgroup analyses, patients were then divided into three groups depending on the number of total RAI: a) Group 4: equal to three times, b) Group 5: four to six times, and c) Group 6: more than seven times. We used SPPSS software to analyze the differences among these groups.
Results: A total of 73 patients, receiving 235 times RAI, were included in the final analysis, among which 52 (69.9%) were female. The mean age was 33±14 (8-68) years old, the mean number of treatment was 3±1.8(3-12)times, , and the mean RAI activity was 22.2±13.3(14.8-88.8)GBq. Complete response was 3 patients (4.1%), partial response was 65 patients (89.0%), and stable disease was 5 cases (6.8%). At the end of treatment, the lesions of 40 patients (54.8%) continued to uptake I-131, while that of 33 patients (45.2%) did not uptake I-131. The median change of stimulated serum Tg of every two RAI (δTg) decreased for 42.84% in the Group 1(109 times), for 34.98% in Group2 (102 times), and for 38.54% in the subgroup of more than twelve months (n=24); there was no significance statistic difference of δTg among three groups (p=0.203). while in subgroup analysis depending on the number of total RAI , median δTg decreased for 50.1% in Group 4 (different time intervals: 45.57%,50.89% and 50.25%, P=0.865), for 36.8%in the Group 5 (different time intervals: 39.71%, 36.09%, and 37.90%, P=0.546), and for 27.7% in the Group 6 (different time intervals: 35.29%, 21.75% and 33.33%, P=0.277); there was statistic difference of δTg among different treatment number (p=0.001). Salivary gland function impairment was significantly associated with increased number of treatment(r=0.363, P=0.001) and increased cumulative dose (r=0.323, P=0.022), while lung function and blood cell count were not statistically different among (P>0.05).
Conclusions: For DTC patients with pulmonary metastases who needs repeated RAI, when serum Tg decreases and then keeps stable under TSH suppression after one RAI, prolonged time to the next RAI did not have significant impact on the efficacy of RAI, although the extent of Tg change becomes weak with RAI number increase. Moreover, prolonged RAI interval might reduce adverse events, and consequently benefit patients.