Thyroid cells use the iodine in food we consume to produce and secrete thyroid hormones into the bloodstream. Iodine is also incorporated into and remains in the thyroid gland. When patients consume radioactive iodine for treatment, the radiation released into the thyroid reduces the number of thyroid cells. As a result, thyroid swelling decreases and the production and secretion of thyroid hormones are reduced. This effect of radioactive iodine is used to treat Basedow’s disease and thyroid cancer. The use of radioactive iodine requires a special facility, and only a limited number of institutions can provide this kind of treatment. Our hospital has provided isotope therapy since 1955.

Radioactive iodine isotope therapy for Basedow’s disease

(1) Therapy schedule

In our hospital, patients can select outpatient or inpatient care. Outpatient care requires hospital visits for two successive days. Receiving care as an inpatient requires hospitalization for one week. In both cases, patients must temporarily observe dietary restrictions on iodine intake as well as halt other medications, including antithyroid drugs (mercazole, Thiuragyl/propacil), inorganic iodine (potassium iodide), and thyroid hormone replacement therapy (Thyradin S). The time period for these changes begins one week before isotope therapy and concludes three days after therapy finishes.

(2) Therapy method

Radioactive iodine capsules are taken orally.

(3) Post-therapy course

The thyroid decreases in size and thyroid hormone levels decline gradually after therapy. However, because hormone levels may fluctuate greatly for 1-6 months following isotope therapy, patients should visit the hospital monthly to adjust medications.
On a long-term basis, this therapy requires a shorter time than other antithyroid medications. Compared to surgery, isotope therapy is more effective and places less of a physical burden on patients.

(4) Complications

• ・Hypothyroidism may develop gradually after isotope therapy.
• ・There is a small possibility that eye symptoms may worsen following isotope therapy. Patients should see an ophthalmologist for evaluation of eye symptoms before therapy begins, and regularly following the therapy.
• ・Because antithyroid drugs are discontinued, thyroid hormone levels may increase during treatment. This can cause symptoms such as palpitations and lethargy. Sufficient caution needs to be exercised in patients who are elderly or suffer other ailments such as heart disease. In such circumstances, we may recommend that patients receive inpatient care at our hospital.

Isotope therapy of malignant tumors (cancer)

Malignant tumors are primarily treated with surgery. However, if cancer cells metastasize to other organs, such as the lungs, the entire thyroid gland will be removed. Thereafter, the patient will undergo isotope therapy.
Cells metastasizing from thyroid cancer incorporate radioactive iodine in the same fashion as the thyroid gland. In the same mechanism as treatment for Basedow’s disease, radioactive iodine is incorporated into and destroys metastasized thyroid cancer cells throughout the body. However, cancerous cells incorporate only a small amount of radioactive iodine. As a result, the dosage of radioactive iodine necessary to be effective in treating cancer is 20 to 30 times greater than that used for the treatment of Basedow’s disease. Also, since not all metastasized cancer cells incorporate radioactive iodine, it is necessary to run tests in advance to determine whether the cancerous cells incorporate iodine.

Isotope ablation

When total thyroidectomy is performed for thyroid cancer, a small amount of thyroid tissue called the “thyroid bed” is sometimes left near the trachea where the thyroid gland was previously located. It has been shown that the destruction (ablation) of this residual portion of the thyroid gland with radiation from radioactive iodine reduces future recurrence. This method is generally used in Western countries. Ablation may be performed in patients with lymph node metastasis or infiltration into surrounding organs; however, this technique is not performed for all patients who undergo a total thyroidectomy.
In Japan, ablation was originally approved only for inpatient treatment. However, restrictions have changed and now it is possible to perform ablation therapy in an outpatient setting as long as certain conditions are fulfilled. Our hospital has been performing outpatient ablation therapy since September, 2011. Thus, we offer both inpatient and outpatient ablation therapy.
In preparation for treatment, patients eat an iodine-restricted diet for two weeks. In general, patients also need to discontinue oral thyroid hormone replacement therapy for approximately four weeks before therapy and may have symptoms of hypothyroidism, such as lethargy, drowsiness, and cold sensitivity. In 2012, however, it became possible to continue hormone replacement therapy by using an injection (Thyrogen*). In this case, an additional two-day examination and costs of the injection are required.

What is Thyrogen?
Thyrogen is a drug that has the same function as thyroid-stimulating hormone (TSH), which stimulates the thyroid to produce thyroid hormones. In isotope testing and therapy, it is important to stimulate the thyroid to incorporate a large amount of radioactive iodine in order to improve the diagnostic accuracy of the examination or increase therapeutic effects. For this purpose, two types of preparation are required: restriction of iodine intake and elevation of blood TSH levels.
Previously, discontinuation of thyroid hormone replacement therapy before an examination or treatment was the only method of increasing TSH levels. However, recently health insurance began covering the drug Thyrogen, a new method of increasing TSH levels. Since this method does not require discontinuation of thyroid hormone replacement therapy, patients do not have to suffer from symptoms of hypothyroidism when undergoing isotope tests and treatment.
Both methods have advantages and disadvantages. We encourage patients to select Thyrogen or cessation of thyroid replacement therapy according to the conditions of their disease.