Radioactive iodine treatment FAQ

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How do I prepare and what are the radiation safety precautions after treatment with I-131 RAI?

  • No special preparation is necessary other than having the proper set up at home to prevent exposure to others (see table below). Your endocrinologist or radiologist should give you detailed instructions on precautions to take depending on the dose of I-131 you receive. 
  • Since RAI produces radiation, patients must do their best to avoid radiation exposure to others, particularly to pregnant women and small children. The amount of radiation exposure markedly decreases as the distance from the patient increases. Patients who need to travel in the days after I-131 RAI treatment are advised to carry a letter of explanation from their physician since radiation detection devices used at airports or in federal buildings may pick up even very small radiation levels.  
  • 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 feces.


Instructions to reduce exposure to others after I-131 RAI treatment

ActionDuration (Days)
Sleep in a separate bed (~6 feet of separation) from another adult1-11*
Delay return to work1-5*
Maximize distance from children and pregnant women (6 feet)1-5*
Limit time in public places1-3*
Do not travel by airplane or public transportation1-3*
Do not travel on a prolonged automobile trip with others2-3
Maintain prudent distances from others (~6 feet)2-3
Drink plenty of fluids2-3
Do not prepare food for others2-3
Do not share utensils with others2-3
Sit to urinate and flush the toilet 2-3 times after use2-3
Sleep in a separate bed (~6 feet of separation) from pregnant partner, child or infant6-23*
*duration depends on dose of I-131 given 

What equipment is used?

None, the patient simply swallows a pill. If the patient has thyroid cancer, they may be asked to follow up with a whole body thyroid nuclear scan 7-10 days after the treatment. Patients being treated for hyperthyroidism do not need such a scan. 

Are there long term risks of I-131 RAI?

In general, RAI is a safe and effective treatment. Hypothyroidism is a common side effect of RAI for hyperthyroidism and always seen after RAI for thyroid cancer (see Hypothyroidism brochure).  Loss of taste and dry mouth due to salivary gland damage may be seen. The use of lemon drops, vitamin C or sour stimulation to potentially decrease the exposure of the salivary glands to RAI may help and should be discussed with your physician. Importantly, once you have been treated with RAI, regular medical follow-up is lifelong.

What are the special concerns for women?

RAI, whether I-123 or I-131, should never be used in a patient who is pregnant or nursing. Pregnancy should be put off until at least 6 – 12 months after I-131 RAI treatment since the ovaries are exposed to radiation after the treatment and to ensure that thyroid hormone levels are normal and stable prior to pregnancy. There is no clear evidence that RAI leads to infertility.

Are there special concerns for men?

Men who receive RAI treatment for thyroid cancer may have decreased sperm counts and temporary infertility for periods of roughly two years. Sperm banking is an option in a patient who is expected to need several doses of RAI for thyroid cancer.


How will I feel after the 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. Also consider sucking on lemon drops for the first 1-3 days after swallowing the pill.  Drink plenty of fluids in the first 24 hours. 


Is there a risk of other cancers from the treatment?

Patients may be at slightly higher risk of acute myeloid leukemia (prevalence of 0.5% between 2 to 10 years after treatment and the risk is considerably lower when smaller I-131 doses are used) (1). In a report of 6840 patients treated in Europe with doses averaging 162 mCi I-131 there was an increased risk of bone and soft tissue cancers (relative risk 4.0), female genital organs (relative risk 2.2), and leukemia (relative risk 2.5) (2). There was no relationship identified with radioiodine and breast disease. Overall, a meta-analysis showed a relative risk of secondary malignancies of 1.19 in thryoid cancer patients given radioactive iodine versus those not treated with radioiodine (3). It is important to note the while cumulative doses of RAI may be associated with a statistically significant increase in second malignancies (relative risk), the actual magnitude of this risk (absolute risk) is very small.

References: (1) Radioiodine-131 in the diagnosis and treatment of metastatic well differentiated thyroid cancer. Maxon HR 3d, Smith HS Endocrinol Metab Clin North Am 1990 Sep;19(3):685-718. (2) Second primary malignancies in thyroid cancer patients. Rubino C, de Vathaire F, Dottorini ME, Hall P, Schvartz C, Couette JE, Dondon MG, Abbas MT, Langlois C, Schlumberger M Br J Cancer. 2003;89(9):1638. (3) Second primary malignancy risk after radioactive iodine treatment for thyroid cancer: a systematic review and meta-analysis. Sawka AM, Thabane L, Parlea L, Ibrahim-Zada I, Tsang RW, Brierley JD, Straus S, Ezzat S, Goldstein DP Thyroid. 2009;19(5):451
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