Radioactive Iodine (I-131) Therapy

What is Radioiodine (I -131) Therapy and how is it used?

Radioactive Iodine I-131 (also called Radioiodine I-131) therapy is a treatment for an
overactive thyroid, a condition called hyperthyroidism. Hyperthyroidism can be caused by
Graves' disease, in which the entire thyroid gland is overactive, or by nodules within the
gland which are locally overactive in producing too much thyroid hormone.

Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive
material to diagnose and determine the severity of or treat a variety of diseases, including
many types of cancers, heart disease, gastrointestinal, endocrine, neurological disorders and
other abnormalities within the body. Because nuclear medicine procedures are able to
pinpoint molecular activity within the body, they offer the potential to identify disease in its
earliest stages as well as a patient’s immediate response to therapeutic interventions.

The thyroid is a gland in the neck that produces two hormones that regulate all aspects of the
body's metabolism, the chemical process of converting food into energy. When a thyroid
gland is overactive, it produces too much of these hormones, accelerating the metabolism.

Radioactive iodine (I-131), an isotope of iodine that emits radiation, is used for medical
purposes. When a small dose of I-131 is swallowed, it is absorbed into the bloodstream in the
gastrointestinal (GI) tract and concentrated from the blood by the thyroid gland, where it
begins destroying the gland's cells.

Radioactive iodine I-131 may also be used to treat thyroid cancer.

Who will be involved in this procedure?

A radiologist who has specialized training in nuclear medicine and others, possibly including
an endocrinologist, thyroid surgeon and radiation safety officer, will be part of your treatment
team.

What equipment is used?

There is no equipment used during radioactive iodine therapy.

Who operates the equipment?

There is no equipment used during radioactive iodine therapy, the patient simply swallows a
prepared dose.

Is there any special preparation needed for the procedure?

You should not eat or drink after midnight on the day of the procedure. If you have been
taking anti-thyroid medications, you must stop at least three days before the therapy is given.
Frequently, the anti-thyroid medication is stopped for five to seven days before therapy.
You will be able to return home following radioactive iodine treatment, but you should avoid
prolonged, close contact with other people for several days, particularly pregnant women and
small children. The majority of the radioactive iodine that has not been absorbed leaves the
body during the first two days following the treatment, primarily through the urine. Small
amounts will also be excreted in saliva, sweat, tears, vaginal secretions, and faeces.

If your work or daily activities involve prolonged contact with small children or pregnant
women, you will want to wait several days after your treatment to resume these activities.
Patients with infants at home should arrange for care to be provided by another person for the
first several days after treatment. Your radiologist can be more specific for your given
situation, but usually this time period is only two to five days.

Your treatment team will give you a list of other precautions to take following your treatment
with I-131. The following guidelines comply with the Nuclear Regulatory Commission:

 Use private toilet facilities, if possible, and flush twice after each use.
 Bathe daily and wash hands frequently.
 Drink a normal amount of fluids.
 Use disposable eating utensils or wash your utensils separately from others.
 Sleep alone and avoid prolonged intimate contact for three or four days. Brief periods
of close contact, such as handshaking and hugging, are permitted.
 Launder your linens, towels, and clothes daily at home, separately. No special
cleaning of the washing machine is required between loads.
 Do not prepare food for others that requires prolonged handling with bare hands.
 If you are breast-feeding, you must stop several days before to ensure that milk
production has also stopped.
 You should avoid becoming pregnant from six months to one year after treatment.
 You must be sure you are not pregnant before receiving I-131. Many facilities require
a pregnancy test within 24 hours prior to giving I-131 in all women of child-bearing
age who have not had a surgical procedure to prevent pregnancy.

Patients who need to travel immediately after radioactive iodine treatment are advised to
carry a letter of explanation from their physician. Radiation detection devices used at airports
and federal buildings may be sensitive to the radiation levels present in patients up to three
months following treatment with I-131. Depending on the amount of radioactivity
administered during your treatment, your endocrinologist or radiation safety officer may
recommend continued precautions for up to several weeks after treatment.

Radioiodine therapy is not used in a patient who is pregnant. Depending on the stage of
pregnancy, I-131 given to the mother may damage the baby's thyroid gland. In such a case,
discussion of the issue with the patient's physician is advised. When given to a nursing
mother, radioactive iodine can reach a baby through her breast milk. Most physicians feel that
this procedure should not be used in women who are breastfeeding unless they are willing to
cease breastfeeding their newborn. Also, it is recommended that pregnancy be delayed until
at least six to 12 months after I-131 treatment.

Women who have not yet reached menopause should fully discuss the use of I-131 with their
physician.

How is the procedure performed?

Treatment for hyperthyroidism is almost always done on an outpatient basis because the dose
required is relatively small.

The radioiodine I-131 is swallowed in a single dose, in capsule or liquid form, and is quickly
absorbed into the bloodstream in the gastrointestinal (GI) tract and concentrated from the
blood by the thyroid gland, where it begins destroying the gland's cells. Although the
radioactivity from this treatment remains in the thyroid for some time, it is greatly diminished
within a few days. The effect of this treatment on the thyroid gland usually takes between one
and three months to develop, with maximum benefit occurring three to six months after
treatment. Usually, a single dose is successful in treating hyperthyroidism. However, rarely, a
second treatment is needed, and very rarely a third treatment may be needed.

What will I feel during this procedure?

Patients may experience some pain in the thyroid after I-131 therapy similar to a sore throat.
You should ask your physician to recommend an over-the-counter pain reliever to treat this
pain, should it occur.

Are there permanent side effects from the procedure?

It is highly likely that some or most of the thyroid gland will be destroyed with this
procedure. Since hormones produced by the thyroid are essential for metabolism, most
patients will need to take thyroid pills for the rest of their life following the procedure.
Thyroid pills are inexpensive, and patients will typically be instructed to take one per day.
There are essentially no other permanent side effects from the procedure.