Clinical outcomes of low-dose and high-dose postoperative radioiodine therapy in intermediate-risk papillary thyroid carcinoma patients with low postoperative stimulated thyroglobulin (1-20 ng/ml) and non-structural or functional metastasis: study protocol for a randomized-controlled trial

Abstract Background: For some intermediate risk papillary thyroid carcinoma patients, if there are structural metastases, reoperation is preferred. If there are functional metastases (131I avidity), they can be treated with high-dose radioactive iodine (131I). However, it is still controversial whether 131I ablation should be used and the determination of 131I dosage for another part of intermediate risk patients with non-structural or functional metastases, especially those with postoperative stimulated thyroglobulin (ps-Tg) 1-20 ng/ml. The aim of the present study is mainly to compare the 3-years disease-free survival between low-dose group (1.1 GBq) and high-dose group (3.7 GBq) in intermediate risk papillary thyroid carcinoma patients with non-structural or functional metastases and ps-Tg 1-20 ng/ml.Methods: A single-center, randomized, double-blind parallel controlled study is designed at the Zhujiang Hospital of Southern Medical University. Participants will be randomized to low-dose group (1.1 GBq) or high-dose group (3.7 GBq) in a 1:1 ratio. After orally receiving different dosage of 131I once on an empty stomach, all patients will return to our hospital every 3-12 months to be performed related inspection items. Discussion: We believe that the 3-year disease-free survival of low-dose group (1.1 GBq) may not be lower than that of high-dose group (3.7 GBq) in intermediate-risk thyroid papillary carcinoma patients with no structural or functional metastases and ps-Tg 1-20 ng/ml. Besides we expect to clarify whether there are apparent differences in successful remnant ablation, efficacy, progression-free survival, safety, and health economics evaluation between the two groups.Trial registration: ClinicalTrials.gov (https://clinicaltrials.gov/), ID: NCT04354324. Registered on 16 April, 2020.