When treating thyroid cancer with iodine 131, especially differentiated thyroid cancer, the risk of postoperative recurrence of thyroid cancer and the advantages and disadvantages of using nuclear therapy should be fully evaluated, so as to avoid “over-treatment” that is not done when treatment is needed, or not done when it is not needed! Iodine 131 therapy should be considered in the following cases: i. distant metastases such as lung and bone; ii. tumor breaking through the true perithelium of the thyroid gland; iii. tumor not breaking through the perithelium but having lymph node metastasis, poor pathological subtypes of papillary carcinoma (high cell, columnar cell, diffuse sclerosis, etc.), multiple carcinoma foci, vascular invasion, non-papillary carcinoma (follicular, low differentiation). IV. Other conditions that are assessed as high risk of recurrence and metastasis after surgery. Note: For those who are older than 45 years old and whether the tumor diameter exceeds 2cm or 3cm, whether these cases must be treated with iodine 131 therapy needs to be combined with clinical risk assessment and cannot be used as indications for iodine 131 therapy across the board. Timing of starting iodine 131 therapy after surgery After the wound has healed, iodine 131 therapy can be performed after avoiding iodine-rich foods (such as seaweed, seaweed, sea fish and other seafood) and stopping taking thyroxine tablets for 1 month. During this period, it is not advisable to undergo enhanced CT examinations and not to eat iodized salt. Preparatory measures needed before treatment Because iodine-containing foods and thyroid hormones can affect the uptake of iodine-131 by the thyroid gland, you should generally stop using thyroid hormones, iodine-containing foods and medications for more than 4 weeks before treatment. In addition, before taking iodine-131 treatment, blood should be drawn to check thyroid function, thyroglobulin (Tg) and globulin antibody (TgAb) and blood count, ultrasound of the neck, plus chest X-ray or CT scan of the chest if necessary. However, enhanced CT examinations are not done – because the enhancer contains iodine, which affects the treatment effect. Focus on protective isolation after iodine 131 treatment. i. Sleep in separate beds for 12 days; ii. Maintain a distance of more than 1 meter from your family for 3 days (assuming 6 hours of contact per day); iii. You can go to work after 5 days (assuming a distance of more than 1 meter from your colleagues and 8 hours of contact per day). It is recommended to extend the above time. However, iodine 131 for medical use is a nuclide with a short half-life, which means that it is metabolized quickly and after 1 month there is no 131 iodine in the body and normal activities can be carried out. Also after taking iodine-131, after urinating and defecating for the first 1 week, flush the bathroom with water more often because a lot of iodine-131 will be discharged from urine and faeces during this time, and irradiate your family. Also, after iodine-131 treatment, it is better to avoid contact with children for one month, especially infants and children.