The purpose of this study is to make a dialectical classification of patients who will receive 131I treatment after operation of thyroid cancer from the point of view of dialectics of syndrome elements of traditional Chinese medicine. By observing the changes of TSH among patients with different syndrome types, investigators can better understand the reasons for the differences in TSH changes among patients. Thus, it provides a basis for putting forward the scheme of stopping taking levothyroxine before iodine treatment, improving the quality of life of patients after radical thyroidectomy, and providing reference for individualized guidance of the timing of radioactive iodine therapy for patients after DTC.

Thyroid cancer is a common thyroid tumor. In the past few decades, the incidence of thyroid cancer in most parts of the world has increased steadily year by year. At present, the best treatment for differentiated thyroid cancer at home and abroad is surgery + radioactive iodine + thyroid hormone replacement inhibition.131I therapy, as an important adjuvant therapy for patients with DTC, can effectively remove the residual thyroid tissue and unresectable local and distant metastatic lesions during the operation.

It is considered that the level of TSH and the time of thyroid hormone withdrawal are important factors affecting the efficacy of radioiodine therapy, and there is a close relationship between the two factors. Clinically, investigators also observed that TSH changes were different in patients who were about to receive iodine treatment after DTC during the withdrawal of thyroxine. In some patients, TSH levels rise rapidly in a short period of time, while others rise slowly. For patients with rapid increase of TSH (sometimes even more than 100uIU/ml), it may promote tumor growth, recurrence and recessive metastasis. Patients with slow rise of TSH may need to constantly review thyroid function until reaching the standard, which brings inconvenience to patients, and withdrawal of drugs for too long will affect patients' physical, psychological and living conditions, resulting in patient discomfort.

In this study, the dialectical classification of TCM syndrome factors was carried out in the patients before radioiodine therapy after DTC. After collecting the patients who met the inclusion and exclusion criteria, they were divided into two groups according to TSH ≤ 30uIU/mL and TSH > 30uIU/mL on the 14th day. The TCM syndrome elements and other clinical information of each group were collected respectively. Investigators will observe the changes of TSH in patients with different types of TCM syndrome factors, and gain a deeper understanding of the reasons for the differences in TSH changes. Investigators hope to provide a basis for putting forward a plan to stop thyroxine before iodine therapy, to improve the quality of life of postoperative patients with thyroid cancer, and to provide a reference for individualized guidance of the timing of radioactive iodine therapy for patients after DTC.

Inclusion Criteria:

1. Study time: June 1, 2021, to January 1, 2022;
2. Study site: The First Affiliated Hospital of Shandong First Medical University;
3. 18-75 years old (including upper and lower limits), male or female;
4. Patients with differentiated thyroid carcinoma diagnosed pathologically after total thyroidectomy
5. Patients with oral levothyroxine tablets ≥ 4 weeks after operation
6. Patients who have stopped taking levothyroxine tablets and whose TSH < 4.2uIU/ml at the time of withdrawal
7. Patients who meet the 131I treatment criteria

Exclusion Criteria:

1. Pregnant or lactating women
2. Patients with various mental disorders, unconscious, etc.
3. Cases with inaccurate information collection

Patients with thyroid cancer who need 131I therapy after operation