The goal of postoperative radioactive iodine (RAI) therapy is to remove postoperative residual thyroid tissue (i.e., “clear nail”) and metastases that could not be removed during surgery (i.e., “clear foci”), thereby reducing the risk of postoperative recurrence or metastases. RAI therapy is followed by lifelong monitoring because:
- The dose of thyroid hormone required after RAI treatment varies from patient to patient and may need to be adjusted dynamically, so regular follow-up monitoring helps your doctor determine the most appropriate dose and make adjustments when appropriate.
- Monitoring for persistence or recurrence of thyroid cancer.
When to monitor?
If there are no signs of recurrence, monitoring is usually done every 3-6 months for 2 years after surgery and at least annually thereafter. The interval may be extended after clinical cure of thyroid cancer [meaning no residual tumor, no lymph node visualization, and thyroglobulin (Tg) levels less than 1 ng/mL].
Many factors, including the size of the primary tumor, the number of metastatic lymph nodes, and the presence of distant metastases, can affect the follow-up schedule. Your doctor will develop a monitoring plan based on your specific situation, and you will need to ask your doctor at the end of each review when your next visit will be, and follow the doctor’s instructions to the letter.
What indicators are monitored?
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At the follow-up visit, the following tests will be done:
Neck check
The doctor will palpate the thyroid growth and probe the neck for abnormal swellings or enlarged lymph nodes.
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Neck ultrasound
Cervical ultrasound can accurately assess the condition of the lymph nodes in the neck and detect the presence of lymph node metastasis in a timely manner, and is the method of choice for monitoring postoperative recurrence of differentiated cancer or lymph node metastasis in the neck.
When an ultrasound is performed, the doctor glides a probe over the neck without causing pain and without radiation. This test is indicated for most patients, including adolescents and pregnant women, among others.
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Fine needle aspiration biopsy
If there are no characteristic ultrasound findings, but there is a high clinical suspicion of cancer, the physician may recommend fine needle aspiration (FNA) of the node to avoid missing the diagnosis.
If the ultrasound suggests suspicious malignancy in the lymph nodes, FNA, or thyroglobulin (Tg) concentration in the aspirate, may be performed, with a positive result suggesting lymph node metastases.
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Blood indicators
Which blood indicators need to be tested are related to the type of thyroid cancer. Of these, Tg is particularly important. It is a protein produced by thyroid cells (both normal and cancerous) and can be used as a “cancer marker”. When the thyroid is completely cleared, Tg levels should be very low or even “undetectable”.
Surgery and RAI treatment
After surgery and RAI treatment, it can take months or years for Tg to drop to zero or “undetectable” levels. If the Tg test is positive, it means that there are still thyroid cells in the body, either normal or cancerous, and your doctor will decide whether to monitor more closely and/or treat them with other tools.
A blood test for indicators of thyroid function can evaluate whether the dose of thyroid hormone is appropriate, and the doctor adjusts accordingly.
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A year after surgery, the frequency of blood tests will be reduced.
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Whole body radioiodine scan
Common sites of metastatic thyroid cancer are the cervical lymph nodes, both lungs, and bones throughout the body. Most recurrent or metastatic lesions of differentiated carcinoma are able to take up iodine. Therefore, a whole-body scan is done within 2 to 10 days after initial RAI treatment to diagnose metastatic or recurrent lesions. The physician may also choose to use it when Tg is elevated after total thyroidectomy and no suspicious lesions are detected by neck ultrasound.
In general, the “specificity” of a whole-body scan can be 100%, meaning that if a whole-body scan finds a lesion, it is usually not “off”; the sensitivity of finding a lesion increases with the dose of imaging agent.
Do all patients need to have a whole-body radioiodine scan at the time of review? There is still controversy in the profession, but the general consensus is that if the risk of recurrence is low (e.g., no iodine uptake outside the thyroid on post-treatment scans, no abnormalities on neck ultrasound, low serum Tg levels), a whole-body scan can be avoided.
What should I look for at the follow-up visit?
What should I look for at follow-up?
At the follow-up visit, you should tell your doctor exactly what you are doing. If you are scheduled for a radioactive iodine scan at your follow-up visit, stop taking thyroxine tablets and eat a low iodine diet 1 month in advance.
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Prompt consultation with a physician is required in the following cases:
- After RAI treatment, you have another serious disease, or you are in poor health.
There is a need to re-evaluate whether to continue RAI therapy, usually after other diseases have been treated and your health has recovered.
- If multiple RAI treatments are required, iodine-containing medications (e.g., amiodarone) need to be stopped for the entire treatment and follow-up period. If other medications are needed, ask your doctor promptly.
- Women of childbearing age should report to their physician if they need to prepare for pregnancy.
- RAI treatment has some side effects, causing radiographic inflammatory reactions such as malaise, dry mouth, neck swelling and discomfort, nausea and abdominal discomfort, and urinary tract damage. The side effects usually occur within a short period of time and subside spontaneously and usually do not require special treatment, but if they are more severe, you will need to consult your doctor.
- RAI treatment may lead to malignancies in the hematological system and other systems. It is important to pay attention to your health during follow-up and consult your doctor if you notice anemia, easy infection, easy bleeding, or other abnormal symptoms.
In addition, it is important to ask your doctor when you encounter some uncertainty during the follow-up visit, and remember not to take matters into your own hands.
Co-author: Dr. Kai Guo, Cancer Hospital of Fudan University