1. If there is too much residual thyroid tissue after surgery, it is recommended to operate again to remove as much residual thyroid tissue as possible; however, those who are contraindicated to surgery or refuse surgery can be treated with iodine 131 directly; 2. Stop using L-T4 for at least 2-3 weeks or use recombinant human TSH (rhTSH) to raise serum TSH to >30 mU/L before iodine 131 treatment; 3. Avoid iodine-containing contrast agents and medications (e.g., amiodarone, etc.) for 1-2 weeks; 4. Perform nuclide whole-body imaging between 2-10 days after iodine 131 therapy; 5. Start (or continue) L-T4 therapy within 24-72 hours after iodine 131 therapy; 6. Avoid pregnancy in female patients for 6-12 months after iodine 131 therapy.