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. Thyroid cells have a special affinity for iodide. After a certain amount of 131 iodine is taken orally, it can be absorbed by the thyroid gland in large quantities, and the radioactive 131 iodine with damaging effects 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 use of radioactive iodine in the treatment of hyperthyroidism.
(1) Diffuse goiter with hyperfunction.
(2) Those who have undergone thyroidectomy in the past and have recurrence; it is not as safe as 131 iodine treatment because there is a greater risk of injury to the recurrent laryngeal nerve or parathyroid glands during surgery.
Those who have serious organic pathologies, such as heart disease, chronic nephritis, hypertension, liver stiffness, chronic bronchitis or lung disease, severe diabetes, mental disorders and organic pathologies of the nervous system, should not be treated surgically.
④Those who are ineffective in long-term treatment with anti-thyroid drugs, or those who are allergic to drugs and should not be treated with drugs or relapse after stopping drugs.
⑤ Those who do not want to operate or are not suitable for surgery.
(6) Patients with severe proptosis (most of the proptosis is reduced after 131 iodine treatment).
3.What are the relative contraindications to radioactive iodine treatment for hyperthyroidism?
Relative contraindications mean that it is better to consider other treatment methods under the following conditions
(1) Nodular goiter with hyperthyroidism and cold nodules confirmed by scan are generally not treated with 131 iodine. Because of the difference in iodine uptake capacity, the dosage of treatment is larger and the results are slightly poorer, often requiring repeated treatment.
②For those with peripheral blood leukocyte count below 3×109/liter, 131 iodine should be used only after improvement by leukocyte promotion therapy.
(3) 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.
(2) Huge goiter has already produced symptoms of tracheal compression, which are often not easily eliminated after taking 131 iodine, and may be aggravated in some cases.
(3) Patients with serious 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 treatment, 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 treatment.
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 when treating hyperthyroidism with radioactive iodine?
The dose used differs 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 (%)].
7. What is the effect 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 60% of patients are cured in one course of treatment and more than 95% in the second course.
8.What should I pay attention to after taking 131 iodine?
In order to obtain the best results in the treatment of hyperthyroidism with 131 iodine, 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 radiation thyroiditis such as itching and pain in the neck can be seen in the early days after receiving 131 iodine treatment, you should avoid looking into or squeezing the thyroid gland in the first week after treatment.
⑤ Avoid prolonged contact with children under 10 years of age within 10 days after taking 131 iodine.
9.What are the early toxic reactions of radioactive iodine treatment for hyperthyroidism?
The treatment of hyperthyroidism with 131 iodine is relatively simple and effective, and most of them have no adverse effects. Adverse reactions are generally divided into two types: 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 to 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.
10.What should I do about 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 this complication is a serious complication of 131 iodine treatment. Most of them occur between 2 and 6 months after treatment, but some occur much later or several years later. Temporary hypothyroidism often recovers on its own, while in a few cases it is permanent and requires lifelong replacement therapy with thyroid preparations.
11. 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 can improve proptosis in most patients (about 70% of reported cases) after treatment, but only in a few cases can proptosis 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.
12. Does radioactive iodine have any effect on fertility and offspring?
The incidence of congenital malformations, stillbirths and prematurity 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. It is not possible to get pregnant 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.
13.Can radioactive iodine treatment for hyperthyroidism cause cancer?
After about 30 years of clinical application of this therapy, the incidence of leukemia and thyroid cancer does not increase compared to the natural incidence of these two diseases. 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 were reported, and their incidence was not higher than the natural incidence of the general population, and these two cases occurred about 1 year after 131 iodine treatment, both with a short onset time, so it is inconclusive whether they are directly related to 131 iodine treatment. Since young patients are more sensitive to radiation, 131 iodine treatment does not directly cause the occurrence of thyroid cancer.