Thyroid cancer: Radioactive iodine (RAI or I131) treatment
1. What is RAI?
RAI (I131) is a radioactive form of the more common iodine that can be found in foods (especially shellfish). Thyroid cells take up iodine much more than any other cell in the body in order to make thyroid hormone. When RAI is taken up by the thyroid, the radioactive iodine destroys the thyroid cells.
2. What are the reasons to use RAI?
The three main reasons to use RAIRAI - radioactive iodine are:
- To destroy or ablate hyperactive thyroid cells in hyperthyroidismHyperthyroidism - overactive thyroid (such as Graves' diseaseGraves' disease - autoimmune overproduction of thyroid hormone resulting in hyperthyroidism)
- To destroy or ablate remaining normal thyroid tissue and thyroid cancer cells after thyroidectomy
- To destroy or ablate thyroid cancer recurrences
In cases of thyroid cancer, RAI can reduce the chance that thyroid cancer will come back (i.e. recur). In cases of papillary thyroid cancer, RAI ablationRAI ablation - the use of radioactive iodine to destroy thyroid cells (either benign or cancer) is recommended if the tumor is over 4 cm in size, extends beyond the borders of the thyroid gland, has spread to the lymph nodes, or if the tumor has spread outside of the neck. RAI is usually not recommended if the cancer is less than 1 cm in size and if there is no evidence of cancer outside the thyroid. There is some controversy as to whether or not cancers between 1 and 4 cm that have not spread outside the thyroid should or those with multiple spots of cancer in the thyroid should be treated with RAI. In these situations, the use of RAI will be determined by your physician.
If you have had total removal of your thyroid for follicular or Hurthle cell cancer, RAI is recommended, unless your follicular cancer was considered "minimally invasive." If you have had total removal of your thyroid for medullary cancer, RAI is not recommended.
3. When and how is RAI performed?
RAIRAI - radioactive iodine is usually done 3 to 6 weeks after surgery, depending on how the patient is prepared for the iodine treatment. The dose of RAI is given by mouth, usually in a pill. One week after receiving the dose, a whole body scan will be performed to show where the iodine collects in the body. Uptake is normally seen in the salivary glands, gastrointestinal tract, and urinary bladder. Normal uptake may also be seen in the liver. Seeing these areas light up on scan does NOT mean that thyroid cancer has spread to these organs.
Figure 4: (left panel) normal RAI uptake in the salivary glands, gastrointestinal tract, and urinary bladder. (right panel) RAI uptake in remnant thyroid
Figure 5: (left panel) RAI uptake in the sides of the neck; may indicate spread of thyroid cancer to lymph nodes
Figure 6: RAI uptake in the middle upper portion of the chest (mediastinum) may be physiologic uptake in the esophagus or thymus or may indicate spread of thyroid cancer to the lymph nodes in the chest
Figure 7: RAI uptake in the lungs or bones may indicate spread of thyroid cancer
Often, uptake is seen in the mid portion of the neck where residual thyroid tissue (i.e. the remnant) is found. (Figure 4) Uptake in the sides of the neck may indicate that cancer has spread to lymph nodes. (Figure 5) Uptake in the upper-middle part of the chest (i.e. mediastinum) may be normal uptake in the esophagus or thymus or may indicate spread of thyroid cancer to the lymph nodes in the chest. (Figure 6) Uptake in the lungs or bones may indicate spread of thyroid cancer to these areas as well. (Figure 7)
4. Will I require multiple treatments?
The initial treatment after surgery is a single dose. You may receive additional doses of RAIRAI - radioactive iodine in the future if you are found to have persistent or recurrent disease.
5. How do I prepare for RAI?
In order for RAIRAI - radioactive iodine to work, residual thyroid tissue must be stimulated to take up as much iodine as possible. This is accomplished by increasing the TSHTSH - Thyroid stimulating hormone; also known as thyrotropin. The hormone that causes the thyroid to make and release thyroid hormone level which tells the thyroid take up iodine to make thyroid hormone. There are two main ways to stimulate thyroid cells that are equally effective:
Thyroid hormone withdrawal
By purposely not taking thyroid hormone replacement after total thyroidectomyTotal thyroidectomy - removal of the whole thyroid for 4 to 6 weeks, the pituitary will naturally respond by increasing the TSH level. It does not "know" that there is no thyroid to make thyroid hormone and keeps trying to stimulate it more and more. In short, the patient is hypothyroid. Towards the end of the withdrawal phase, patients will be very hypothyroid and may feel very tired, fatigued, unmotivated, etc. Many physicians will put patients on the shorter acting thyroid hormone (T3, Cytomel) for 2 to 4 weeks followed by no hormone for 2 weeks in order to reduce the amount of time the patient is symptomatic. The TSH level is then checked to ensure adequate stimulation before RAI treatment. A TSH >30 is recommended before RAI. Thyroid hormone is restarted 2 to 3 days after taking the dose of RAI.
Injections of recombinant TSHRecombinant TSH - injections of TSH (brand name - Thyrogen) in order to accomplish TSH stimulation before giving RAI. (or ThyrogenThyrogen - injections of TSH (brand name - Thyrogen) in order to accomplish TSH stimulation before giving RAI stimulation) involves giving a man-made form of TSH to stimulate the thyroid. This method allows patients to avoid the symptoms of hypothyroidismHypothyroidism - underactive thyroid seen with thyroid hormone withdrawalThyroid hormone withdrawal - not taking any thyroid hormone after a total thyroidectomy (so called thyroid hormone withdrawal), so that your brain will naturally increase its production of TSH; in preparation for RAI therapy. Typically two doses of Thyrogen are given on two consecutive days followed by the RAI dose on the third day.
The choice of which technique to use will depend on a discussion with your physician and his or her expertise. To maximize iodine uptake, a low iodine diet is recommended for 1-2 weeks prior to RAI. This is very important. Information about low iodine diets may be obtained on the Thyroid Cancer Survivors Association website (www.thyca.org).
Do I have to be in the hospital?
Treatment can be performed on an outpatient basis provided the patient can stick to certain radiation precautions (see below).
What radiation precautions are required?
In the first week after treatment, the RAI comes out of the body in the urine, saliva, and sweat. It also comes out in breast milk, so breast-feeding after RAI is not recommended. Typical recommendations for the first 3 to 5 days after RAI include:
- Do not share a toilet/bathroom. Sit down with urination and flush twice with the lid down.
- No exchange of saliva through kissing or food sharing.
- No prolonged close contact (<3 feet) with others, particularly pregnant women and children.
- Sleep alone.
- Refrain from sexual activity.
- Wash clothes, towels, and linens separately.
- Drink plenty of fluids, suck sour candy and chew gum to clear the unused iodine from your body.
- Shower/bathe and wash hands frequently.
What are the potential side effects of RAI?
Mild nausea, salivary gland swelling, and pain may occur within the first 24 hours after RAI. Some patients also complain of dry mouth, or change/loss of taste. RAI will NOT cause hair loss.
Does RAI cause cancer?
There is a small risk of developing a second, different cancer (i.e. other than thyroid) after RAI. This risk increases with cumulative doses of RAI greater than 400 to 500 mCi. One benefit of Thyrogen stimulated RAI is that it decreases the radiation dose delivered to unwanted areas of the body, compared to RAI after thyroid hormone withdrawal.
Can I get pregnant after RAI?
Yes. There is no increased risk of infertility or birth defects after RAI. The typical recommendation is to wait 6 months to one year after RAI before getting pregnant. There may, however, be an increased risk of miscarriage or menstrual irregularities during that 6-month period.