This study is a phase III randomized controlled clinical trial on the role of adjuvant radiotherapy in high-risk locally advanced differentiated thyroid cancer. Patients who meet the inclusion criteria were randomly assigned 1:1 to either the experimental group (adjuvant radiotherapy+RAI) or the control group (RAI), with LRFS as the primary endpoint of the study.

Inclusion Criteria:

1. The patient voluntarily joined this study and signed an informed consent form;
2. Age: ≥ 14 years old,<80 years old, male or female not limited;
3. Histopathological diagnosis of differentiated thyroid cancer;
4. Surgical total or near total thyroidectomy;
5. The surgery did not achieve R0 resection, and R1/ R2 resection was performed. The volume of residual tumor in R2 resected patients is less than 2cm3;
6. The main organ functions are normal;
7. Good compliance and cooperation with follow-up.

Exclusion Criteria:

1. Previously received radiation therapy for the head and neck area;
2. Differentiated thyroid cancer with poorly differentiated, or undifferentiated components;
3. There is distant metastasis;
4. Previously received 131I treatment;
5. Previously received or currently receiving targeted therapy, immunotherapy, chemotherapy;
6. Within 5 years or simultaneously suffering from other active malignant tumors. Cured local tumors, such as skin basal cell carcinoma, skin squamous cell carcinoma, superficial bladder cancer, prostate carcinoma in situ, cervical carcinoma in situ, breast carcinoma in situ, can be included in the group;
7. Pregnant or lactating women;
8. Other physical illnesses that affect patients' ability to receive standard treatment;
9. According to the researchers' assessment, there may be other factors that could force the subjects to terminate the study, such as suffering from other serious illnesses (including mental illnesses) that require concurrent treatment, severe abnormal laboratory test values, family or social factors that may affect the safety of the subjects or the collection of experimental data;
10. Individuals with claustrophobia who are unable to undergo radiation therapy;
11. Patients deemed unsuitable for inclusion by other attending physicians.