Radioactive iodine therapy (RAI), also known as radioiodine remnant ablation (RRA), is a treatment some patients with papillary or follicular thyroid cancer may receive after thyroidectomy. RAI or RRA is administered to destroy remaining (or remnant) thyroid cells after surgery. This treatment is considered effective in properly selected patients because the thyroid cells are the main cells in the body that absorb iodine. When the thyroid cells absorb the radioactive iodine, the cells are destroyed (ablated, ablation).
Before RAI or RRA, you and your doctor have a choice about how treatment is administered: (1) with Thyrogen® [Genzyme Corporation], or (2) Traditional RAI/RRA. The purpose of both treatments is to destroy remaining thyroid cells after thyroid cancer surgery, or to aid in the diagnosis of a recurrence of thyroid cancer. The information below explains both options.
Thyrogen is a drug administered before radioactive iodine therapy (or RRA). RAI/RRA is performed to destroy (ablate) remaining (remnant) thyroid cells after thyroid cancer surgery (eg, thyroidectomy). Thyrogen is a recombinant human form of thyroid-stimulating hormone (TSH). The biological term recombinant is related to molecular cloning. Furthermore, Thyrogen may be used in the diagnosis of recurrence of well-differentiated thyroid cancer with RAI or RRA. Well-differentiated means the cancer cells resemble normal cells and grow more slowly than undifferentiated cancer cells (abnormal looking cells).
Thyrogen allows you to keep taking your thyroid hormone replacement medication (eg, levothyroxine) before, during and after radioactive iodine therapy or radioiodine remnant ablation. You can avoid experiencing the signs or symptoms of hypothyroidism, which can improve quality of life.
When Thyrogen is utilized to test/diagnose possible thyroid cancer recurrence, the injection is given on days 1 and 2. On day 3 RAI is administered, and on day 5 a blood test with or without a whole body scan. Of course, similar to any medical test, there is the risk for a diagnosis to be missed.
Side effects may include: nausea, fatigue, vomiting, dizziness.
Traditional radioactive iodine therapy or radioiodine remnant ablation may be utilized to destroy thyroid cells after thyroidectomy and/or test for recurrence of thyroid cancer. RAI or RRA requires you to stop taking your thyroid hormone replacement medication (eg, levothyroxine). Medication may be withheld for 4 to 6 weeks.
When thyroid hormone medication is withheld, you become hypothyroid (hypothyroidism). Signs and symptoms of hypothyroidism may be slight to severe, and may include:
Why withhold thyroid hormone medication? The purpose of withholding thyroid hormone replacement medication is to increase your level of thyroid-stimulating hormone (TSH). It may be necessary for you to go without your thyroid hormone replacement medication for weeks. Furthermore, some doctors recommend a low-iodine diet for several weeks prior to radioactive iodine therapy (radioiodine remnant ablation). Reducing foods containing iodine sets up iodine-starved thyroid cells to absorb the radioactive iodine. Foods to be avoided include iodized salt (or foods containing same), dairy products, fish/seafood, soy products, and foods made with red dye (food coloring).
Your doctor recommends where radioactive iodine therapy (radioiodine remnant ablation) is administered: hospital or outpatient facility. As early as 4 weeks after thyroid surgery, radioactive iodine therapy or radioiodine remnant ablation may be administered. The common type of radioactive iodine is I-131 (iodine 131). It is administered in capsule form taken by mouth and swallowed. The exact dose of I-131 is determined by your doctor.
Today, most patients have their treatment in an outpatient setting and are allowed to go home the same day. However, because therapy is radioactive, you are given precise instructions that include staying at home and away from people for several days until the I-131 becomes inactive.
Side effects may include: nausea, swelling/pain in the neck where thyroid cells remain, dry mouth, temporary loss of smell and/or taste. Rare side effects are infertility in women who receive a high dose of I-131 and cancer years after treatment.
Bridget Brady, MD, FACS is the first fellowship-trained endocrine surgeon in Austin, Texas. She has a passion for and expertise in disease of the thyroid, parathyroid, and adrenal glands. Dr. Brady has performed thousands of thyroidectomies and parathryoidectomies with a focus on minimally invasive techniques to optimize patients’ medical and cosmetic outcomes.
Managing thyroid cancer with Thyrogen® (thyrotropin alfa for injection). Thyroid Cancer Survivors' Association, Inc. http://www.thyca.org/.
Pacini F, Landenson PW, Schlumberger M, Driedger A, et al. Radioiodine ablation of thyroid remnants after preparation with recombinant human thyrotropin in differentiated thyroid carcinoma: results of an international, randomized, controlled study. J Clin Endocrinol Metab. 2006;91:926-932.