Ablation with Low-Dose(1.1GBq) and High-Dose(3.7GBq) Radioiodine in Postoperative Low and Intermediate Risk Differentiated Thyroid Cancer

Objectives To compare the remnant ablation success rate with low- (1.1GBq) and high-dose (3.7GBq) radioiodine in postoperative low and intermediate risk differentiated thyroid cancer.

Methods Inclusion criteria were an age of 18 years or older, after total thyroidectomy and appropriate extent of neck lymph node dissection, low and intermediate risk DTC(T1N0~1M0, T2N0M0), including papillary and follicular thyroid cancer, receiving ¹³¹I therapy for the first time. Exclusive criteria were the presence of aggressive malignant variants(e.g., tall cell, insular, columnar cell carcinoma, poorly differentiated carcinoma, diffuse sclerosing variant, anaplastic thyroid carcinoma, medullary thyroid cancer), patients suffered from other tumor. Patients were randomly assigned to one group: low-dose or high-dose radioiodine group, radioactive ¹³¹I were administered at a dose of 1.1 GBq or 3.7 GBq, depending on the study group. Thyroid ablation was assessed 6 months after radioiodine administration. Successful remnant ablation were defined by a stimulated serum thyroglobulin of <1ng/mL in absence of interfering thyroglobulin antibodies, with or without confirmatory nuclear or other imaging studies, or suppressed thyroglobulin of <0.2 ng/mL with negative neck ultrasonography. An alternative definition in cases where thyroglobulin antibodies were present, was the absence of visible radioiodine uptake on a subsequent diagnostic radioiodine scan. Statistical analysis was performed by Frequencies, Crosstabs and chi-square test.

Results 120 patients were enrolled from October 2014 to June 2015. A total of 111 patients with data that could be evaluated(29 males and 82 females; 19-75 years old; 54 patients received low-dose radioiodine and 57 patients received high-dose radioiodine ). A neck ultrasound scan, diagnostic whole-body scanning and serum thyroglobulin assay (off thyroid hormone therapy) , or suppressed thyroglobulin with neck ultrasound scan were performed approximately 4 to 8 months after the initial ¹³¹I therapy. Thyroid ablation was complete in 91 of the 111 patients (82.0%), 43 patients in the low-dose group and 48 patients in the high-dose group. The successful ablation rates were 80.0% and 84.2% respectively, and there was no significant difference between the two groups(P=0.530﹥0.05).

Conclusions The remnant ablation success rate between low- (1.1GBq) and high-dose (3.7GBq) groups had no significant difference in postoperative low and intermediate risk differentiated thyroid cancer.