Radioactive Iodine Therapy for Feline Hyperthyroidism

  • Is the gold standard for treatment
  • Is more cost effective than other treatment options
  • Produces little or no stress during treatment
  • Eliminates all thyroid tumor tissue regardless of location
  • Does not affect normal thyroid tissue
  • Does not affect other tissues or organs in the body
  • Produces no harmful side effects
  • Avoids the complications and inconvenience of surgery or medical therapy
  • Results in normal thyroid function usually within one month

We look forward to helping you and your cat get back to a healthy, happy, long life.

Your cat’s veterinarian will need to refer your pet for treatment.  To make an appointment or to inquire about the Center, please call our toll-free number at 1-877-RADCATS (723-2287) or (919) 967-9261 and ask to speak to one of our Radiation Treatment Technicians.  You may also email questions to

Frequently Asked Questions

■      What is Feline Hyperthyroidism?

■      What are my treatment options?

■      How does the radioactive iodine cure hyperthyroidism in my cat?

■     What are the expected results of the treatment?

■     Is my cat a candidate for treatment?

■      What pretreatment evaluation is needed?

■      What is the cost and how do I pay?

■      What arrangements will I need to make to have my cat treated?

■      What happens while my cat is at the center?

■      What precautions are necessary when my cat returns home?

■      How will I know if my cat is cured?


What is Feline Hyperthyroidism?

Feline Hyperthyroidism is one of the most common endocrine disorders in middle-aged and older cats. Reports estimate that one in three hundred cats are affected by hyperthyroidism. The thyroid glands are located in the neck and produce hormones that regulate cellular metabolism in all organs of the body.

The amount of thyroid hormone produced by the thyroid glands is regulated by the pituitary gland in the brain. The pituitary gland signals the thyroid glands to maintain proper levels of circulating thyroid hormone. This mechanism keeps cellular metabolism in balance. Most cases of feline hyperthyroidism are due to benign tumors called nodular hyperplastic goiters.

These tumors produce excess thyroid hormone and do not respond to regulation by the pituitary gland. Unfortunately, the thyroid tumor cannot always be palpated in the neck. Some cats will have thyroid tumor in the chest or other locations in the body. Any of these tumors can produce excessive amounts of thyroid hormone.

The signs and symptoms of hyperthyroidism are multi-systemic and relate to increased metabolic changes. Hyperactivity, weight loss, increased appetite, increased thirst, increased elimination, vomiting, diarrhea, panting, rapid heart rate, increased shedding, and occasionally lethargy have been observed. High blood pressure is a common clinical finding. Blindness due to retinal hemorrhage and heart disease (including heart failure) may also be associated with hyperthyroidism. Untreated hyperthyroidism is fatal.


What are my treatment options?

  • Iodine 131 therapy is the optimal treatment for hyperthyroidism in cats. It is the safest and most effective treatment currently available. A single dose of iodine 131 results in a rapid return to normal thyroid function in most cats.
  • Surgical Treatment is limited to the removal of tumor tissue in the neck region and carries several risks. In addition to the anesthetic risk for older cats and the stress of surgery, there can be post-operative complications affecting surrounding structures. Damage to or removal of the parathyroid glands can cause hypocalcemia and can lead to seizures. Damage to regional nerves can also cause paralysis of the vocal cords. The estimated cost of surgery is between $900 and $1,400. In cases where one affected gland is removed, 70% of the cats develop tumors in the other gland or at other sites in the body.
  • Medical Management does not cure the disease. To properly regulate hormone levels, anti-thyroid drugs must be given daily for the pet’s lifetime once they’ve developed disease.. If medication is stopped, hyperthyroid symptoms return. Undesirable side effects such as vomiting, itching, hair loss, and serious blood disorders can occur. Frequent blood chemistry monitoring and dose adjustment are required. The cost for medical therapy and monitoring often exceeds $1,000 per year.


How does the Iodine 131 treatment cure hyperthyroidism in my cat?

Iodine 131 emits beta particles that kill cells instantly. The beta particles can only penetrate distances of one to two millimeters. The only organ in the body that uses iodine is the thyroid gland. The tumor cells are destroyed as they trap radioactive iodine. Normal thyroid tissue has become dormant due to suppression by the pituitary gland. Since the normal thyroid tissue is dormant, only the tumor cells take up the iodine 131. Destruction of the tumor cells allows the normal thyroid tissue to return to normal function over several months.


What are the expected results of the treatment?

More than 95% of cats given a single dose of iodine 131 will return to normal thyroid function within three months of treatment. Some cases can take longer to return to normal thyroid function. A small percentage of cats treated with iodine 131 will not be cured with one dose. These cats may have a thyroid carcinoma. Carcinomas often do not respond to one dose of iodine 131. Cats with thyroid carcinomas will usually be cured after a second treatment given three to four months after the initial treatment.

Adverse effects associated with the treatment are rare. There may be mild discomfort in the neck and difficulty swallowing for a few days due to transient thyroiditis. Permanent hypothyroidism can occur, but this is usually limited to cats with significantly elevated thyroid levels before treatment. These cats require higher doses of iodine 131 to destroy the tumor.

Hyperthyroidism often masks signs and symptoms of other diseases. Removing the symptoms and laboratory abnormalities associated with hyperthyroidism can allow your veterinarian to better evaluate your cat for other common medical conditions.  Speak to your cat’s veterinarian about a 30 day medical trial of anti-thyroid medication to help rule out underlying diseases.

Observable changes in cats after successful treatment may include weight gain, better hair coat and grooming habits, normal appetite, an absence of vomiting, and a greater tendency to "cat nap" during the day and sleep at night.


Is my cat a candidate for treatment?

Radcats Treatment Center accepts medically stable cats for treatment. Cats with kidney disease or symptomatic heart disease must be evaluated carefully. Your veterinarian will decide if your cat is a candidate for treatment.


What pretreatment evaluation is needed?

We request the following from your veterinarian:

  • Physical examination and complete medical and surgical history
  • Complete Blood Count and Serum Biochemistry panel
  • Urinalysis with specific gravity
  • Diagnostic T4 level (absolute value) from a reference laboratory, not an in-house T4

Laboratory tests performed within 30 days of treatment are required for accurate iodine 131 dosing. If any additional testing is needed we will contact your veterinarian.

If your cat has been on an anti-thyroid drug like methimazole (Tapazole®), please stop the medication 3 days before your appointment.


What is the cost and how do I pay?

The current fee, as of January 1, 2018, is $1600. This includes the iodine 131 treatment and hospitalization during treatment. This does not include any other medical procedures or services. We will contact you and your veterinarian if we feel we need to perform any other medical procedures while your pet is with us.

A $600 deposit is necessary when the appointment is made to guarantee the dose of iodine 131 and the treatment date. This deposit is fully refundable if the appointment is rescheduled or canceled by noon on Friday prior to the treatment date. The balance is due upon admission to the Center. We accept cash, personal checks, MasterCard, Visa, American Express, and Care Credit.


What arrangements will I need to make to have my cat treated?

Once we have received the pretreatment laboratory information from your veterinarian you can call to schedule a date for treatment. If your veterinarian has not sent results, we will call and request the information. Some cats may benefit from sedation prior to a drive or an airplane trip to the Center. You and your veterinarian can make this decision. Please make sure any sedatives for the trip home are sent with your pet.

What happens while my cat is at the center?

When you and your cat arrive you will be greeted by our Receptionists who will introduce you to one of our Radiation Treatment Technicians. Our technician will explain procedures, answer questions, and review any special requests you may have. You will have the opportunity to meet Dr. Anderson and discuss any concerns you may have regarding treatment.

We have a variety of foods on hand to help ensure that even the most finicky eater will be pleased. Should your cat have specific preferences or dietary needs, please bring that special food. Items such as toys and blankets may be left with your cat for the duration of the stay. Please be aware that these items cannot be returned to you.

We will shave a small area of hair on your cat's side prior to the injection. We will then give a precise amount of Iodine 131 subcutaneously or under the skin. This injection is comparable to an annual vaccination. An iodine 131 technician will call you with an update after dosing.

During the rest of the treatment time, your cat will enjoy soft music in our comfortable, climate-controlled radiation isolation facility. This facility has its own backup generator to ensure your cat remains comfortable during any power outages. Our radiation technicians will visit all cats twice daily to feed, water, change litter pans, pet, and read cards from home.

Because cats treated with iodine 131 release radiation during their stay, access to the isolation facility is strictly limited to our trained radiation personnel who wear radiation monitoring devices at all times. State radiation safety protocols do not allow visits or tours of the actual treatment center. You are welcome to call us to check up on your pet and to pass on any pats or messages from home. We are happy to give you a tour of the main hospital and show you the accommodations your pet will have during his or her stay.

Radiation safety regulations mandate that we keep cats in our isolation facility until their levels of radiation do not pose a threat to human health. Most cats will stay at the center at least 3 days. We will begin measuring radiation levels 2 days after treatment. We will call you as soon as your cat may be discharged. Your cat may stay with us a total of 14 days post-treatment at no additional charge for your convenience.

Hyperthyroid cats are older citizens and owners are often concerned their pets will not fare well during their hospitalization. Rest assured we will attend to any need your pet may have. You may even leave recordings so your pet can hear your voice during his or her stay. We will also read any notes or cards you may want to send.


What precautions are necessary when my cat returns home?

We suggest common sense safety precautions for the 10 days following your pet's return home. Confine your cat to the house. Limit close contact between your cat and people. Use gloves and litter pan liners, and double bag litter in plastic bags. Do not let your cat sleep with you. Pregnant women should have no contact with your cat or the litter box for 21 days. A more detailed set of guidelines is included with the release form you will receive when your cat is discharged.


How will I know if my cat is cured?

A blood sample to check the serum thyroid hormone levels will be taken by your veterinarian 30 days and 90 days after treatment. Your veterinarian will send this information to us. Most cats have normal values at the 30-day evaluation although some cats can take 2 to 3 months to return to normal levels.