HOW CAN FELINE HYPERTHYROIDISM BE TREATED?
Hyperthyroidism can be treated medically, surgically or with radioiodine. Medical treatment consists of administration of methimazole 2 or 3 times per day for the life of the cat. Surgery consists of the removal of one or both lobes of the thyroid gland. Radioiodine treatment consists of 1 injection of radioiodine.

WHY WOULD RADIOIODINE BE USED INSTEAD OF MEDICINE OR SURGERY?
Medical therapy is effective for the majority of cats but there can be several reasons it is not the best choice. First, some cats are simply impossible to pill. Secondly, a few cats have reactions to the medication (blood or liver problems.) Finally, some owners may not want to have to medicate their relatively young cat for the rest of its life.

Surgery can present several problems. Many hyperthyroid cats have heart problems and are not the best anesthetic risks. If both lobes of the thyroid gland are removed at once there is a risk that there will be temporary damage to the associated parathyroid glands resulting in temporary hypocalcemia (low blood calcium.) This complication can be life threatening. Surgery that removes only 1 of the 2 lobes of the thyroid gland at a time can minimize this risk but results in the need for 2 surgeries. A few cats have thyroid tissue in unusual sites (ectopic thyroid tissue) which may not be surgically accessible. Finally, there is a small risk that the condition will reoccur.

Radioiodine therapy has some distinct advantages over the other methods of treatment but it also has at least one drawback. The advantages are that it eliminated the need for lifetime medication, there is no chance that the patient will develop a problem with the antithyroid medication, it eliminates the need for anesthesia and the risk of hypocalcemia (low blood calcium.) The major drawback is that it requires a brief period of isolation from the family. There is minimal risk (less than 1%) that the condition will reoccur.

HOW DOES RADIOIODINE THERAPY WORK?
Iodine is an element required for normal health. In the body it is used primarily by the thyroid gland (located in the neck) to produce thyroid hormone (thyroxin.) The major effect of thyroid hormone is regulation of metabolic rate. When present in excess, thyroxin is toxic to many organs including the heart and liver. Untreated, hyperthyroidism may lead to death. (decay) in which it gives off radiation and becomes an inert element, Xenon. The radiation given off consists of 2 types: Gamma rays (similar to x-rays) and beta particles (electrons.) The half-life of I-131 is 8 days; that is one-half of the radioiodine goes through this process every 8 days.

When injected in the body a large percentage of radioiodine is accumulated into the thyroid gland. The bulk of the remainder is excreted primarily in the urine and to a lesser degree the feces. That which is concentrated in the thyroid gland emits radiation. The beta particles are particularly lethal to the thyroid cells. The gamma rays also effect the thyroid but many escape the cat's body. The radiation kills the thyroid cells and thus treats the hyperthyroid condition.

ARE THERE ANY RISKS INVOVLED?
The incidence of reaction to radioiodine is reported to be extremely low.

HOW IS THERAPY ADMINISTERED?
The radioiodine is administered by injection and your cat is placed in isolation. Your pet is then monitored over the next few days until her/his radioactivity level is low enough to permit his/her return to you.

WHAT DO I DO ON THE DAY OF THE TREATMENT?
Bring your cat to the hospital. Your primary care veterinarian will have performed all or the majority of tests necessary before treatment. If further tests are required they can be performed that day and treatment scheduled for another day soon. If your cat has been on methimazole (Tapazole) or propylthiouracil (PTU) he/she must be off this medication for at least 1 week prior to treatment. IF he/she is on heart medication this should be continued through the morning of therapy.

IS RADIOIODINE THERAPY EXPENSIVE?
The cost of any treatment for feline hyperthyroidism is significant. The cost for radioiodine therapy is $1225. This includes the radioiodine itself, the hospitalization in isolation and the monitoring. Tests required prior to therapy are not included. This compares reasonably with most fees for surgical removal using the 2-surgery approach. The cost of medication would average approximately $275 per year plus the cost of repeat blood tests.

HOW LONG DOES THE ISOLATION PERIOD LAST?
The usual period is from 3 to 5 days.

ARE THERE ANY SIDE EFFECTS OF THERAPY?
Side effects are extremely rare.

WHAT HAPPENS AFTER THE ISOLATION IS OVER?
Upon discharge your cat will still be minimally radioactive. This will decrease to undetectable levels over a period of 2 to 3 weeks. Even though the level of radioactivity is very low (much lower than the level at which human patients are discharged from hospitals), you still must exercise prudence during this period. You should scoop the litter box daily wearing plastic or rubber gloves. You MUST use clumping litter and dispose of the waste down the toilet. DO NOT put waste in the regular trash. You should not sleep with your cat during this period. Your hands should be washed after petting your cat.

CAN THE HYPERTHYROIDISM EVER REOCCUR?
Yes. Although it is very uncommon, some cats with extreme hyperthyroidism can have only a partial response to treatment or have reoccurrence. In cases where this is thought to be a potential problem, surgical removal of one thyroid lobe prior to radioiodine therapy may be recommended. If there is only a partial response or reoccurrence, repeat therapy is usually successful.

WHAT AFTERCARE WILL MY CAT NEED?
Almost no cats require specific aftercare. Your primary care veterinarian will test your cat's thyroid in 2 weeks. These results usually show a low level. Normal levels take a while to reappear. It is very unlikely that thyroid supplements will ever be needed. Periodic rechecks should be sufficient afterwards.

DISCHARGE INSTRUCTIONS FOR CATS THAT RECEIVED RADIOIODINE
Your cat has been injected with radioiodine (Iodine-131) for the treatment of its hyperthyroidism. It has been maintained at the Animal Medical Center at Cooper City since its treatment so that the radioactivity would decrease to a point that it was safely practical for your cat to be returned to your household. It is important for you to take proper steps in its care to protect you, your family and your cat.

Much of the remaining radioactivity will disappear due to the normal process of radioactive decay. Until this is complete your cat is emitting a very low level of radiation. This will not harm you unless you expose yourself to it at very close rages for prolonged periods of time. Therefor, do not sleep with your cat in your bed for the next 2 weeks. If you should find that he or she has sneaked in one night, do not be alarmed. However, it is important that you make every effort to prevent this and it not occur again. If you cannot prevent your cat from sleeping with you, your pet should be boarded. You should contact your primary care veterinarian for this service.

Some of the minimal residual radioiodine will be eliminated through the urine and feces. It is important that you change the litter daily and not get any urine or feces on your hands or clothes. We require that scoopable litter be used during this period and that all wasted be flushed down the toilet. DO NOT DISPOSE OF THE WASTES IN THE TRASH! You must wear gloves when changing your cat's litter box. We will be happy to provide plastic gloves for you to wear when you do this or you may wear commercially available rubber gloves. After changing the litter please wash the gloves under copious amount of running water. Do not touch your face or mouth with gloves or fingers that have touched your cat's urine or feces and have not been thoroughly washed.

If you have any concerns or questions about these instructions you should call immediately. We will be happy to check your cat's level of radioactivity at any time upon your request.

WHAT ARE THE BENEFITS OF RADIATION THERAPY?
Radiation therapy shrinks and destroys cancers that are not affected by chemotherapy alone or cannot be surgically removed. In some instances permanent control of the tumor is possible through the use of radiation therapy. In other cases, even when a cure is not possible, radiation therapy can still bring a measure of relief. Shrinking a large tumor with radiation therapy may improve the quality of life by reducing pressure, bleeding or pain.

ARE THERE RISKS INVOLVED?
There are risks involved with any type of treatment for cancer. Some normal cells will be killed by the radiation in addition to cancer cells. Some side effects may be apparent because of the normal cells being killed. Usually the side effects are outweighed by the benefits.

In addition, radiation therapy requires that your pet be perfectly still during each treatment. Thus, general anesthesia is required for each treatment. Your pet will be fully evaluated to assess any unusual anesthetic risks. While there is always a minimal risk associated with general anesthesia, nearly all cancer patients withstand this aspect of the treatments very well.

HOW IS THERAPY ADMINISTERED?
In radiation therapy, a machine directs a high-energy radiation beam to the cancer and some normal tissue around it. each series of treatments is specifically designed for the individual patient.

IS RADIATION THERAPY EVERY COMBINED WITH CHEMOTHERAPY?
Yes. Some tumors have been shown to be more responsive if chemotherapy is given in combination with radiation. Dr. Burk and Dr. DiBernardi will discuss this with you if your pet's tumor is one in which this might be useful.

WHAT DO I DO ON EACH DAY OF TREATMENT?
Specific arrangements will be made with you as to when your pet should be presented and picked up daily. While we will work to minimize difficulties, you should plan to drop your pet off each morning and leave him/her for the day. Your pet should not have food after midnight and should only have a limited amount of water on mornings of treatment days. Routine morning medications should be administered even on treatment days.

WILL MY PET BE RADIOACTIVE AFTER A TREATMENT?
No! In no way will your pet ever be radioactive after a treatment. The radiation does its damage to the cells during the treatment and does not leave any residual radioactivity.

WHO PERFORMS THE RADIATION THERAPY TREATMENTS?
The decision as to whether or not radiation (alone or in concert with other therapies) will be made by you with the consultation and guidance of our Oncologits. If radiation therapy is selected, your pet will go through a series of steps to develop an individualized treatment plan. The first treatment will be performed by the Oncologist and Chief Radiation technologist. After the first treatment the technologists will perform the remaining treatments under the doctors' direction. The doctors will monitor your pet's progress and are always available for your questions.

IS RADIATION THERAPY EXPENSIVE?
Treatment of cancer with irradiation can be costly. It involves complex equipment as well as the expertise of highly trained, specialized veterinary professionals. The exact cost of a pet's treatment will depend upon the type of tumor he/she has and the therapeutic prescription. You will have a thorough discussion with Dr. Burk or Dr. DiBernardi about all fees and a fee estimate will be given to you before any therapy is instituted.

HOW LONG DOES RADIATION THERAPY TAKE?
Radiation therapy for most tumors is administered as a series of treatments over a period of six to seven weeks. This schedule helps protect normal healthy tissues and increases the effect in tumor tissue. The total dose of radiation used and the number of treatments, called fractions, in which the total dose is administered depends upon many factors such as size and location of the tumor, the type of tumor, and the general health of your pet.

WHAT STEPS ARE TAKEN DURING THE TREATMENT PERIOD?
After radiation therapy has been chosen as a method of treatment there will be a number of steps taken before treatment is actually started. In most cases a staging procedure consisting of a series of standard and special radiographs will be made to more clearly delineate the size and extent of tumor so that therapy can be designed to cover the entire tumor and a small margin of normal tissue. Next, a treatment simulation will be performed. During the simulation you pet will be anesthetized and positioned on the treatment couch. A series of x-rays and adjustments will be made to determine the optimum position of the radiation source and your pet. THE DYE MARKS ALL TREATMENTS HAVE BEEN COMPLETED! After the simulation, your pet's Oncologist will use the data from the staging studies and the simulation with our radiation therapy-planning computer to develop an optimized treatment plan for your pet. Then, your pet will begin having her/his daily treatments as prescribed.

WHAT ARE THE EFFECTS OF TREATMENT?
During treatment we will monitor the effect of the radiation on the cancer as well as on the surrounding normal tissues. It may become necessary to alter the plan because of changes in the tumor or normal tissues. But this is usually not necessary. Most side effect that occur during radiation therapy are usually not serious but may be unpleasant.

Most pets will develop skin changes in the area being treated. A redness of the skin will probably develop. This may progress to a dry flakiness or even a moist redness, similar to eczema. If moistness does develop your pet may want to scratch at it. If this occurs we will give you medications or recommend over the counter preparations to control the problem. If it develops the moistness and scratching usually subsides in 7 to 10 days after therapy is completed. Hair loss in the treated area is common and may be permanent. More commonly, the loss persists for 3 to 6 months and then hair starts to slowly regrow. It may regrow in lighter or darker than its original color.

It is unusual for pets to become nauseated or have vomiting and diarrhea as a result of radiation therapy. In this sense pets are much more fortunate than people having radiation therapy. In those cases that do develop such symptoms medication is usually effective in relieving the problem.

When cancer of the oral or nasal cavity is treated with radiation therapy a foul odor may develop as the cancerous tissue is destroyed. The odor is temporary and decreases after the bulk of the tumor is killed.

Radiation will affect the lacrimal (tear) and salivary glands if they are in the radiation field. The effects will be a decrease in production and a change in texture to a thicker consistency. Eye lubricants will be prescribed if problems with tears develop. Problems with saliva can usually be handled by providing adequate water for drinking.

CAN THE RADIATION THERAPY CAUSE CANCER IN LATER YEARS?
While it is theoretically possible for this to happen, it would be extremely unlikely. This usually requires decades to occur in people and is extremely rare in pets.

WHAT DO I DO IF PROBLEMS DEVELOP DURING TREATMENT?
During regular business hours, call the hospital and ask to speak with Lisa. If she is not familiar with the problem (which will be unusual since she has years of experience with radiation therapy) she will have Dr. Burk or Dr. Dibernardi return your call.

WHAT HAPPENS AFTER TREATMENT IS OVER?
It is important for pet's Oncologist to examine your pet after radiation therapy is completed. The first post treatment exam is performed 10 to 14 days after treatment. Further exams will be scheduled periodically thereafter. This will allow normal tissue side effects to be detected before they become advanced, and the effect of the radiation on the tumor to be evaluated. It is the goal of radiation therapy to completely eradicate the cancer. In some pets this happens and no evidence of tumor persists. In other pets the cancer or lump may never completely disappear but its growth is arrested and the tumor is controlled. You will also need to have your pet examined periodically by your primary care veterinarian for regular vaccinations, worming, heartworm prevention, flea control, or any illness.

Finally, it is important to keep in mind that our goal is to provide additional months or years of comfortable, happy life for your pet with cancer. Radiation therapy, although an involved process, is a means for achieving the goal in many cancer patients. Dr. Burk,Dr. DiBernardi, Lisa and the staff at the VSSF are committed to working with you to achieve this goal.