Due to different treatment methods, the dosage used is relatively different. When treating hyperthyroidism, the dose of 131 iodine should be calculated separately based on the treatment method and the patient's specific conditions. The main reference factors include thyroid weight, maximum iodine uptake rate of the thyroid gland, effective half-life, etc. The calculation formula is as follows:
Dose [microcurie (μCi) or becquerel (Bq)] = [planned μCi or Bq/gram of thyroid × thyroid weight (gram) × 100]/[maximum iodine uptake by the thyroid Rate(%)].
Thyroid weight estimation is difficult, including estimation by palpation and calculation by scanning. Generally, a thyroid gland with degree I to II enlargement weighs 30 to 40 grams; a thyroid gland with degree II to III enlargement weighs 40 to 80 grams. Even the error of thyroid radionuclide imaging can reach 20%. Because the thyroid uptake of 131I and the effective tracer dose are not consistent with the treatment dose, there are many influencing factors, and clinical adjustment still needs to be based on experience.
When treating hyperthyroidism, the dose of 131I has a decisive role in the treatment effect and complications. The following factors have an important influence on dosage.
(1) For severe hyperthyroidism, the dosage should be appropriately increased, and for those with mild hyperthyroidism and short course of disease, the dosage should be appropriately reduced.
(2) Older people have poor sensitivity to 131I, so the dose can be increased during treatment. Younger people, with high sensitivity, can reduce the dose.
(3) Antithyroid drugs and iodide can reduce the sensitivity of the thyroid to radioactive 131I, thereby affecting its efficacy; for those who have taken antithyroid drugs and iodide, the dose of 131I should be appropriately increased; Patients without any treatment are highly sensitive and should appropriately reduce the dosage.
(4) The hard thyroid gland has low sensitivity to 131I, so the dose of 131I should be appropriately increased during treatment.
(5) For patients with postoperative recurrence, the effective thyroid tissue is mixed with scars, and the dose can be appropriately reduced.
(6) If the 131I uptake rate in the thyroid site is low and the effective half-life is short, the treatment dose can be increased appropriately.
(7) Nodular hyperthyroidism has poor sensitivity to radiation, so the dose should be increased appropriately.