Diagnosis of Thyroid Cancer and Treatment with I-131
What is radioiodine I-131 treatment?
Radioiodine I-131 treatment is a time-tested and effective treatment for the two most common types of thyroid cancer – papillary and follicular. Most people have radioiodine I-131 for thyroid cancer after having surgical removal of all or part of the thyroid or for recurring thyroid cancer. Treatment with radioiodine I-131 can find remnant and metastasized cancer and destroy it by targeting the cancer cells and eliminating them wherever they may be.
What types of thyroid cancer are treated with radioiodine I-131?
Thyroid cancer is a rare type of cancer that starts in the cells of your thyroid gland. There are different types of thyroid cancer cells that are identified by a laboratory examination of biopsied tissue under a microscope. Two of these types of cancer, papillary and follicular thyroid cancer, take up iodine and can be treated with radioiodine I-131.
- Papillary thyroid cancer
This is the most common type of thyroid cancer, accounting for about 80% of cases. It usually grows slowly and is more common in women and younger people.
- Follicular thyroid cancer
This type is less common than the papillary variety, accounting for about 15% of thyroid cancers. It tends to grow faster and is more likely to spread to other parts of the body. It is more common in older people and in regions of the world where iodine intake is low.
Medullary and anaplastic thyroid cancers are uncommon varieties of thyroid cancer that do not take up iodine and require other forms of post-surgical treatment, such as chemotherapy, targeted therapy, or immunotherapy.
Diagnosis of thyroid cancer
Thyroid cancer can be discovered in several ways:
- A health care provider may feel a nodule or swelling during a physical examination of the neck and thyroid gland.
- A blood test can measure the levels of thyroid hormones and other factors.
- While most thyroid nodules do not cause symptoms, you may experience:
- A lump or swelling in the neck.
- Changes in voice, such as hoarseness or difficulty speaking.
- Trouble swallowing or breathing.
- Pain in the neck or throat.
- Swollen lymph nodes in the neck.
- Imaging tests, such as ultrasound, CT scan or MRI, are often performed to check the size and shape of the thyroid gland and look for any nodules or abnormal growths. Some thyroid cancers are found when a patient has an imaging exam for another reason and the radiologist notices a mass or nodule on the thyroid. This is called an incidental finding.
A fine-needle aspiration biopsy will confirm if and what type of thyroid cancer you have. This involves taking a small sample of tissue from the thyroid nodule or mass and examining it under a microscope. While thyroid nodules are common, they are usually not cancerous.
Treatment for thyroid cancer
After your medical team determines the type and stage of thyroid cancer you have, there are several options for treatment, including surgery to remove all or part of the thyroid, radiation, chemotherapy, hormone therapy, and targeted therapy. Your cancer care team will guide you on the best treatment for your cancer. For a detailed explanation of types of thyroid cancer and their treatment, please visit:
- The Thyroid Cancer page on the American Thyroid Association’s website
- The Thyroid Cancer Treatment page on National Cancer Institute’s website
After you have completed your initial treatment for papillary or follicular thyroid cancer, your cancer care provider may recommend treatment with radioiodine I-131, a well-established and widely used treatment for hyperthyroidism and thyroid cancer since its introduction in the 1940s. I-131 can find and eliminate thyroid cancer cells throughout the body that might have been missed by other treatments.
Treatment for thyroid cancer with radioiodine I-131
Radioiodine (radioactive iodine) therapy is a molecular radiology treatment that uses a radioactive form of iodine called iodine-131 (I-131) to destroy remaining thyroid cancer cells after surgery. The thyroid gland and thyroid cancer cells absorb nearly all the iodine in your body, so radioiodine I-131 can target them specifically without affecting other organs.
Radioiodine I-131 treatment can extend lives and improve quality of life for people with papillary or follicular thyroid cancer that has spread to the neck or other parts of the body (metastasized).
How does radioactive iodine therapy work?
Radioiodine therapy works by taking advantage of the fact that thyroid cells are very efficient at absorbing and storing iodine from your diet. When you swallow a capsule or liquid containing I-131, it travels into your bloodstream and reaches your thyroid gland. There, it is taken up by the thyroid cancer cells and emits radiation that damages or kills them. I-131 can also find metastasized thyroid cancer cells throughout the body and eliminate them.
The amount of radiation delivered by I-131 depends on the dose you receive and how much iodine your thyroid cells take up. The dose is calculated based the type and extent of your thyroid cancer, as well as other factors. Your healthcare provider will monitor your response to the treatment using blood tests and scans.
The radiation from I-131 is very targeted, so it mainly affects your thyroid gland, nearby tissues, and other thyroid cancer cells in your body. Most of the excess I-131 that is not absorbed by your thyroid cells is eliminated from your body through urine within a few days.