1. What is the principle of radioactive iodine treatment for hyperthyroidism?
Radioactive 131 iodine was first used as a treatment for hyperthyroidism in 1942, and it is an effective anti-thyroid drug. The thyroid cells have a special affinity for iodide, so after a certain amount of 131 iodine is taken orally, it can be absorbed by the thyroid gland in large quantities, and the damaging radioactive 131 iodine can be seeded into the thyroid tissue. 131 iodine, when decaying into 131 xenon, can radiate beta rays (99%) and gamma rays (1%). The former has an effective range of only 0.5 to 2 mm, and can selectively destroy the epithelium of the thyroid vesicles without affecting the adjacent tissues. Therefore, some people call 131 iodine treatment for hyperthyroidism as “internal thyroid surgery”.
2. What are the indications for radioactive iodine treatment of hyperthyroidism?
The following conditions must be met for the treatment of hyperthyroidism with radioactive 131 iodine.
(1) Patients with Graves’ hyperthyroidism.
(2) Adolescent patients with Graves’ hyperthyroidism who are allergic to antithyroid drugs, or who have poor efficacy of antithyroid drugs, or who have relapsed repeatedly after treatment with antithyroid drugs, or who have relapsed after surgery.
(3) Patients with Graves’ hyperthyroidism with leukocytopenia or thrombocytopenia.
(4) Patients with Graves’ hyperthyroidism with atrial fibrillation.
(5) Patients with Graves’ hyperthyroidism combined with increased rate of 131I uptake in Hashimoto’s disease
3. What are the relative contraindications to radioactive iodine treatment for hyperthyroidism?
Relative contraindications mean that other treatments are best considered under the following conditions.
(1) Nodular goiter with hyperthyroidism, with cold nodules confirmed by scan, is generally not treated with 131 iodine. Due to the difference in iodine uptake capacity, the dosage of treatment is larger and the effect is slightly poorer, and repeated treatment is often required. In such cases, surgical removal should be considered first.
(2) In severe cases of hyperthyroidism, thyroid crisis and heart failure may be induced, so it is better to control the symptoms with anti-thyroid drugs before 131 iodine treatment.
4. What are the absolute contraindications to radioactive iodine treatment for hyperthyroidism?
Radioactive 131 iodine therapy is not indicated for the following conditions.
①Women during pregnancy and lactation. When 131 iodine is ingested by the mother, it can enter the thyroid gland of the fetus or infant through the placenta and breast milk, causing cretinism in the fetus and infant.
②Patients with acute myocardial infarction.
③Patients with severe liver and kidney diseases.
5. What preparations should be made before radioactive iodine treatment for hyperthyroidism?
The following preparations should be made in advance for the treatment of hyperthyroidism with radioactive iodine.
①It is advisable to avoid iodine and other iodine-containing foods or drugs 2 to 4 weeks before taking 131 iodine.
②If the condition is serious before 131 iodine therapy, with heart rate over 160 beats/minute and significantly elevated serum T3 and T4, it is advisable to first treat with anti-thyroid drugs or insulin, etc., and wait for the symptoms to be reduced before using 131 iodine therapy.
③Patients using anti-thyroid drugs need to stop taking them, for example, stopping tabazol for about 3-5 days, and stopping PTU for 2 weeks, and then making 131 iodine uptake rate measurement, followed by 131 iodine treatment.
④ Perform routine blood and urine tests, chest X-ray, etc. to understand the function of major organs.
⑤ Perform thyroid uptake rate of 131 iodine and thyroid scan in order to calculate the drug dose.
⑥Explain to the patient the precautions related to 131 iodine treatment.
⑦For a few days before and after taking 131 iodine, the patient should rest in bed and avoid strenuous activities.
6. How to calculate the dose of radioactive iodine in the treatment of hyperthyroidism?
The dosage used varies depending on the treatment method. In the treatment of hyperthyroidism, the dose of 131 iodine should be calculated according to the method of treatment and the patient’s specific situation. The main reference factors are the weight of the thyroid gland, the maximum rate of 131 iodine uptake by the thyroid gland, and the effective half-life. The calculation formula is as follows.
Dose (μCi or Bq) = [plan μCi or Bq/g thyroid x thyroid weight (g) x 100] / [maximum thyroid iodine uptake rate (%)
The estimation of thyroid weight is difficult and includes estimation by palpation and calculation by scanning. Generally, an enlarged thyroid gland of degree I to II weighs 30 to 40 grams; an enlarged thyroid gland of degree II to III weighs 40 to 80 grams. Even the error of thyroid radionuclide imaging can be up to 20%, because the thyroid uptake of 131 iodine and the effective tracer amount is not consistent with the treatment amount, and there are many factors affecting it, which requires some experience.
7. Why is the dose of radioactive iodine adjusted in the treatment of hyperthyroidism?
When treating hyperthyroidism, the dose of 131 iodine is decisive for both treatment outcome and complications. The following factors have an important influence on the dose.
①Severe hyperthyroidism requires an appropriate dosage increase, while mild hyperthyroidism with a short duration of disease requires an appropriate dosage reduction.
② Older people with poor sensitivity to 131 iodine can increase the dosage in treatment, while younger people with high sensitivity can reduce the dosage.
③Anti-thyroid drugs and iodide can reduce the thyroid’s sensitivity to radioactive 131 iodine? s sensitivity, thus affecting its efficacy; for those who have taken antithyroid drugs and iodide, the dose of 131 iodine should be increased appropriately; for patients with high sensitivity without any treatment, the dosage should be reduced appropriately.
④Hard-textured thyroid gland has low sensitivity to 131 iodine, and the dosage of 131 iodine should be increased appropriately during treatment.
⑤ Post-operative relapsed patients with effective thyroid tissue adulterated with scars may reduce the dosage appropriately.
(6) Those with low 131 iodine uptake rate in the thyroid area and short effective half-life, the treatment dose can be increased appropriately.
(7) Nodular hyperthyroidism has poor sensitivity to radiation, and the dose should be increased appropriately.
8. What are the methods of administration of radioactive iodine for hyperthyroidism?
The route of administration is usually oral. There are many kinds of dosing methods, such as one-time dosing method, standard dosing method and multiple small dosing method, etc. Most of them are based on the calculated one-time dosing method.
One-time dosing method: the calculated dose of the drug is taken orally on an empty stomach at one time, this method is effective, short course of treatment, more commonly used at home and abroad. When the total dose is not more than 10 millicuries (mCi) and the clinical symptoms are not serious, the one-time dosing method is used, and food can be eaten only 2 hours after taking the drug to avoid affecting the absorption of the drug. If the disease is heavy and the drug dose is more than 10 mCi, 2/3 to 1/2 can be taken first, and then the remaining dose can be taken after 2 to 3 days, and the interval between the second administration should not be too long.
Multiple small dose method: For hyperthyroidism patients not according to the patient’s condition, 131 iodine 2 millicuries is given every few weeks until the clinical symptoms are relieved. This method has long delay, poor effect, high dosage, and no reduction of hypothyroidism complications, so it is less used clinically.
Standard dose method: For all patients with hyperthyroidism, regardless of the patient’s condition, 131 iodine is administered at 3-4 millicurie at the first treatment. Although this method takes into account the differences in individual sensitivity, the course of treatment is long and the efficacy is not well predicted.
9. What is the effectiveness of radioactive iodine treatment for hyperthyroidism?
If the indications for treatment of hyperthyroidism with 131 iodine are properly selected, the dosage and delivery method are correct, and the patient and doctor cooperate with each other, the efficiency is more than 90%. After taking the medication, the effect will appear in 3-4 weeks, and then the symptoms will decrease month by month, the thyroid gland will shrink and the weight will increase. Generally, about 50% to 80% of patients are cured in one course of treatment, and about 20% to 40% are cured in the second course of treatment.
10. How to repeat treatment after taking 131 iodine?
After taking 131 iodine, it takes more than 3 months for thyroid function to return to normal, and in some cases, it takes 6 months to a year for the patient to be in remission, and about 2/3 of cases can be cured at once, while 1/3 of cases need 2 or more courses of treatment. After the first dose of 131 iodine, a second treatment should be considered only after an interval of at least 6 months, depending on the patient’s condition, in order to reduce the occurrence of complications of hypothyroidism. The dose of the second treatment should be based on the response to the first treatment. If the first 131 iodine dose is insufficient, the dose of the second treatment should be increased by about 50% of the first dose; if the first treatment improves and then the patient relapses, the dose of the second treatment should be increased by 25% compared to the previous one; if the symptoms improve but not cured, the dose of the second treatment can be estimated according to the situation. In principle, the calculation of the dose after the second time is the same as the second time.
11. What should I pay attention to after taking 131 iodine?
In order to obtain the best efficacy of 131 iodine in the treatment of hyperthyroidism, it is necessary to pay attention to the following aspects.
①Eat only after 2 hours of taking 131 iodine on an empty stomach to avoid affecting the absorption of iodine.
②After taking 131 iodine, the therapeutic effect usually starts to appear after 3 weeks. During the period before the clinical symptoms start to improve, it is not advisable to use iodine, bromine and anti-thyroid drugs arbitrarily, so as not to affect the reabsorption of 131 iodine and reduce the therapeutic effect. A low iodine diet for 2 to 4 weeks after treatment and no sea plants such as seaweed and nori.
③Patients should take rest, avoid strenuous activities and mental stimulation, and prevent infection for a few days after taking 131 iodine.
④Since symptoms of radioactive thyroiditis, such as itching and pain in the neck, can be seen in the early stage of 131 iodine treatment, you should avoid looking into or squeezing the thyroid gland during the first week after treatment.
12. What should I do if I take too much radioactive iodine by mistake?
Overdose of 131 iodine during hyperthyroidism treatment can lead to thyroid crisis and hypothyroidism, so it must be treated immediately. The principles are
①Block the accumulation of 131 iodine in the thyroid gland: take 200-300 mg of potassium perchlorate orally 3 times a day or 40 mg of potassium iodide once a day.
(ii) Blocking the organicization of 131 iodine in the thyroid gland: oral tabazol 20 mg 3 times a day for 3 to 5 days.
③Accelerate the clearance of 131 iodine by kidney, reduce the reabsorption of 131 iodine in the body, drink more water, and use diuretic drugs such as glucose, mannitol and dihydrocotrimoxazole to accelerate the excretion of 131 iodine.
13. What are the early toxic effects of radioactive iodine treatment for hyperthyroidism?
The treatment of hyperthyroidism with 131 iodine is simple and effective, and most of them have no adverse effects. Adverse reactions are generally divided into early toxic reactions and late complications. Early toxic reactions refer to reactions that occur within 2 weeks after taking the drug, and are commonly seen as follows.
① Systemic reactions are often dominated by digestive system symptoms, such as anorexia, nausea, vomiting, etc. A few have skin pruritus, rash, dizziness, malaise, etc., which can disappear in 2-3 days with symptomatic treatment.
②Local reactions are more common, mainly the manifestation of thyroid edema and radiation thyroiditis. Patients have itching in the neck, swelling and pressure, and even pain in the lower throat and cough, which do not require special treatment and gradually disappear after a few days or 1 week.
(3) During the first 2 weeks of treatment, some patients may experience increased symptoms (elevated basal metabolic rate and serum protein-bound iodine concentration), which can gradually improve with bed rest or application of some sedatives and some beta-blockers such as benzodiazepines. Individual serious patients may develop hyperthyroid crisis, manifested as mental agitation, high fever, sweating, accelerated heart rate (often above 140 beats/min), increased pulse pressure, and even atrial fibrillation, diarrhea and coma, etc., which can often be life-threatening if not treated in time. This is due to the destruction of thyroid follicles by radioactive damage and the release of large amounts of thyroxine into the blood or many other factors. For patients with severe clinical symptoms and a large thyroid gland, thioureas should be administered before 131 iodine is given and should be closely monitored when 131 iodine is given.
④ Leukopenia, which mostly occurs after a single dose of 131 iodine, can generally be gradually recovered.
What should be done for hypothyroidism after radioactive iodine treatment?
Hypothyroidism is very simple to treat and can be easily corrected by giving thyroxine tablets.
Hypothyroidism is one of the late complications of 131 iodine treatment, and most of them occur between 2 and 6 months after treatment, but some occur later or several years later. The incidence of hypothyroidism after 131 iodine therapy is reported to be different at home and abroad, but the incidence increases gradually with time after treatment. In China, it was reported that the incidence of long term hypothyroidism was 25% for 2-5 years after 131 iodine treatment, which is related to the gradual development of hypothyroidism with age due to the natural failure of thyroid disease itself. Currently, with the standardization of iodine-131 treatment, the incidence of hypothyroidism is generally around 5-15%.
One of the possible reasons for hypothyroidism is that ionizing radiation damages the nucleus of the thyroid epithelial cells so that they cannot divide and regenerate, and the longer the treatment, the more hypothyroidism will occur. How to reduce the occurrence of hypothyroidism after 131 iodine treatment is still a problem that has yet to be solved.
15. Can radioactive iodine treatment for hyperthyroidism aggravate proptosis?
Severe progressive proptosis can occur spontaneously or after subtotal thyroidectomy, but less frequently after 131 iodine treatment. 131 iodine improves proptosis in most patients (reported to be about 70%), but only in a few cases does it worsen. It is generally believed that 131 iodine causes a gradual decrease in thyroid function, so that thyrotropin or proptosis-producing substances in the pituitary gland do not increase suddenly, which is why some scholars consider hyperthyroidism with significant proptosis to be an indication for treatment with 131 iodine.
16. Does radioactive iodine have any effect on fertility and offspring?
The incidence of congenital malformations, stillbirths and premature births in the offspring is not increased, and the incidence of infertility is not significantly different from that of the normal population. Although the radiation damage from a single treatment is not as great as that from a single gastrointestinal fluoroscopy, many scholars have conducted more in-depth studies. Patients treated with 131 iodine have been observed to have chromosomal variants that can gradually return to normal. Therefore, the risk of increasing genetic mutations and chromosomal aberrations after 131 iodine treatment is very low. However, considering the long-term effects of ionizing radiation, genetic effects, long-term follow-up observation is also needed to draw the correct conclusion. In order to protect the health of the next generation and intergenerational children, it is necessary to include pregnancy as a contraindication to 131 iodine treatment. Pregnancy is not allowed during the treatment period, and it is generally recommended that it is perfectly safe to consider a childbirth plan after 3 months of treatment when the radioactivity in the body drops below the background, more than 6 months after treatment.
17. Can radioactive iodine treatment for hyperthyroidism cause cancer?
The incidence of leukemia and thyroid cancer has not increased compared to the natural incidence of these two diseases after about 30 years of clinical application of this therapy. One group of data showed that the incidence of thyroid cancer was 0.5% in 22714 cases in the 131 iodine treatment group, 0.5% in 11732 cases in the surgical group, and 0.3% in 1238 cases with anti-thyroid drugs. Among nearly 60,000 cases of hyperthyroidism treated with 131 iodine in China, only 2 cases of leukemia have been reported, and their incidence rate is not higher than the natural incidence rate of the general population, therefore, 131 iodine treatment does not directly cause the occurrence of thyroid cancer.