In thyroid cancer, a distinction is made between differentiated carcinomas (papillary and follicular) and undifferentiated carcinomas (anaplastic). There is also C-cell carcinoma (medullary). Women are affected twice as often as men. The probability of developing thyroid carcinoma increases with age. The treatment of thyroid cancer consists of three pillars: surgery, radioiodine therapy, and lifelong intake of thyroid hormones. The primary treatment for thyroid cancer is surgery. In the case of thyroid cancer, removal of the thyroid gland is generally indicated. In the case of de-differentiated thyroid carcinoma, radiotherapy of the neck is usually carried out after surgical removal of the thyroid gland.

Aim of radioiodine therapy

It is hardly possible to remove the entire thyroid gland surgically. Radioiodine therapy can completely remove the remaining thyroid residue. Radioiodine therapy is also used if the tumor recurs in the area of the original operation or in cases of metastases. A prerequisite for successful therapy is the uptake of iodine-131, which is only the case with differentiated thyroid carcinomas. The location of iodine-storing tissue is documented by whole-body scintigraphy.

Preparation for radioiodine therapy

In a detailed discussion with the doctor, the planned thyroid examinations, lifelong medication with thyroid hormones, and regular follow-up care are discussed with the patient. Before the first radioiodine therapy, the size of the remaining thyroid tissue is determined using ultrasound. Subsequent scintigraphy is used to visualize the residual thyroid tissue to be treated and assess its storage behavior. A new operation must be considered if the level of retention exceeds 20%.

When can radioiodine therapy be carried out?

The first radioiodine therapy to remove the remaining thyroid gland takes place around 4-6 weeks after the thyroid operation. At this point, there is a significant reduction in thyroid hormones in the blood. This reduction is the most essential prerequisite for carrying out radioiodine therapy (TSH > 30 µU/ ml). For this reason, you must not receive any thyroid hormones, iodine-containing medication, or iodine-containing contrast media after the operation and before the planned radioiodine therapy. A diet low in iodine is recommended. Any thyroid hormone preparation taken in the meantime must also be discontinued 4 weeks before any necessary follow-up radioiodine therapy in the event of recurrence, lymph node metastases, or distant metastases, or alternatively, a hormone preparation (Thyrogen) must be given twice before therapy. Which of the two procedures can be used depends on the individual tumor classification and the current constellation of findings. Please note that driving is prohibited in the case of hypothyroidism.

When should radioiodine therapy not be carried out?

Radioiodine therapy is not adequate for tumors with a lack of iodine storage (usually medullary, dedifferentiated, or differentiated oncocytic thyroid carcinoma). This therapy is not used during pregnancy and breastfeeding. Therapy cannot be carried out if there are problems with radiation hygiene (urinary incontinence, need for care).

Radioiodine therapy

On the day of therapy, you should not have eaten for at least six hours beforehand. You will be given a capsule containing radioactive iodine-131 for treatment in the application room on the therapy ward. This is absorbed from the bloodstream by the thyroid remnant and is intended to destroy both the thyroid cells remaining after the operation and any micro-settlements that store iodine. One and a half hours later, you can eat again. The destructive radiation effect (ß-radiation) only has a range of a few millimeters. However, as gamma radiation is also produced simultaneously, and the staff should not be exposed to unnecessary radiation, we ask you to keep as much distance as possible during the treatment. Your thyroid dose rate is measured using a detector mounted in the ceiling above the bed. Your whole-body dose rate will be determined in the morning so that you know your approximate time of discharge. The duration of the inpatient stay for radioiodine therapy ranges from 3 to 5 days, in some cases up to 10 days. During your stay, the current value of the tumor marker (thyroglobulin) will also be determined. After the therapy, a whole-body scintigraphy is carried out on the day of discharge to monitor the treatment. Any metastases outside the thyroid gland are imaged and treated with radioiodine therapy. The effects of radioiodine therapy last up to three months.

Possible side effects of radioiodine therapy

High-dose radioiodine therapy can rarely lead to temporary inflammation of the thyroid gland and tumor remnants. These symptoms, usually mild, can be treated well with anti-inflammatory medication and an ice pack. As the salivary glands absorb some of the radioactive iodine, they can also become inflamed. Temporary inflammation of the stomach lining can occur. To prevent this, please drink enough fluids and stimulate your salivary flow, especially during the first few days of radioiodine therapy. Occasionally, a temporary change in the white blood count is observed. In 10-20% of patients treated with high-dose radioiodine therapy, there is an explicit permanent restriction of saliva production, especially in the parotid glands (sicca syndrome). The occurrence of leukemia (1%) is dose-dependent. In patients with metastases in the lungs, scarring may occur due to repeated high-dose radioiodine therapy (< 1%). In men, reduced sperm production is rarely observed with high-dose therapies. There is no evidence of increased malformations or other adverse effects in pregnancies following radioiodine therapy. However, suitable contraception should be used 6-12 months after the last radioiodine therapy to allow for any necessary renewed application of radionuclides.

Follow-up care

Despite the successful completion of the first radioiodine therapy for a differentiated thyroid carcinoma with an unremarkable whole-body scintigraphy and a thyroglobulin level that is no longer measurable, lifelong follow-up care is necessary. We will be happy to accompany you during this time. Follow-up care aims to detect a possible carcinoma recurrence or the occurrence of metastases in a timely manner.

Approximately four months after treatment, a consultation with the doctor, a physical examination, and an ultrasound of the neck are carried out as part of the tumor follow-up. Diagnostic iodine whole-body scintigraphy is then carried out on an inpatient basis to assess the response to therapy. It is imperative to monitor the lifelong intake of thyroid hormones, which must be observed with the tumor marker thyroglobulin. Calcium levels are checked regularly in patients with a post-operative parathyroid hormone deficiency.

Prognosis

The prognosis depends on the stage of the tumor, the histological type, and the patient's age. Younger patients have a significantly better prognosis.

The prognosis for differentiated thyroid carcinomas is generally excellent. The 10-year survival rate for papillary thyroid carcinomas is reported to be between 85 and 90 %, and between 75 and 80 % for follicular carcinomas. Local recurrence occurs in 5 - 20 % of cases, and metastases in 10 - 15 %.

Exemplary case study on radioiodine diagnostics: