Feline Hyperthyroidism is a disease of the thyroid gland that affects older cats of all breeds. The symptoms are due to excessive secretion of thyroid hormones T3 (triiodothyronine) and T4 (thyroxine) which affect several body systems by increasing their metabolic rate. Hyperthyroidism is now one of the most frequently diagnosed diseases of the cat.

Symptoms include weight loss (over 80‰) in spite of a normal or ravenous appetite. Most are hyperactive, restless, anxious and easily stressed. Cardiopulmonary signs are tachycardia, heart murmurs, congestive heart failure, panting and difficult breathing. Vomiting is more often seen than diarrhea. Simultaneous kidney disease is often present.

Left untreated, hyperthyroidism can result in severe debilitating disease and death. Appropriate and effective treatment, on the other hand, can prevent and resolve these symptoms. A diagnosis of hyperthyroidism is made by history, recognition of clinical signs, and thyroid function tests: increased total T4 and/or free T4. Additional tests are sometimes needed to evaluate the heart, kidneys and gastrointestinal tract.

Radiotherapy for Feline Hyperthyroidism
Recovery from hyperthyroidism without treatment does not occur. If left untreated, the hyperthyroid cat will progress to emaciation, severe metabolic and cardiac disease and death. In hyperthyroid cats that are medically stable, radiotherapy with the radioisotope Iodine-131 is the safest and most effective method of treatment.

A simple injection of a small volume of iodine-131 is made under the skin. The I-131 is specifically metabolized by the thyroid tissue and destroys the abnormal thyroid cells without damage to other tissues. Because the patient is radioactive after this injection, state law requires special hospitalization under strict confinement for 3-5 days, until the radioactivity is measured below acceptable patient release levels.

Methemazole (Tapazole) vs I-131 Treatment

Treatment Facility
I-131 treatment requires a special isolated and radiation-shielded treatment and hospitalization room. The radioiodine treatment room at Sugar Land Veterinary Specialty and Emergency Center is specifically designed for the purpose of radiation safety and patient comfort. The cat cages are glass-backed and positioned against windows that provide a view of the walled and landscaped exercise yard through 1 ½" thick plate glass.

Six special feline cages with plate glass backs against leaded windows for a view, resting platform and litter room, and a trough drain for easy decontamination of spills, litter and wastes allow our personnel to manage the hyperthyroid case load more efficiently.

The cages each have litter compartments which allow our technician to feed and change litter daily in a less time, thus keeping technician exposure time to minimum levels. A special air-conditioning and heating unit plus a strong exhaust system keep the air in this room separate from the rest of the facility.

Closed circuit video monitoring is used to observe our patients throughout their treatment period without the need for personnel to be in the radioactive treatment room. Additional radiation detection and survey equipment is needed to ensure safe and effective handling of the radioiodine. Animal waste and bedding materials will become contaminated and then require special handling, storage, monitoring and disposal.

A Radioactive Material (RAM) license has been issued to Sugar Land Veterinary Specialists by the Texas Department of State Health Services, Radiation Control Program, after a thorough screening and documentation process.

A linear accelerator, also called a LINAC, is a large and very heavy machine used to create a uniform, very high energy x-ray beam used to treat cancer in all parts of the body. These x-rays can destroy cancer cells while sparing the normal surrounding tissues.

The x-ray beam is projected from the LINAC Head, which is part of the gantry which rotates around the patient while delivery the tumor dose of radiation. 

The x-ray beam is shaped by our integrated multi-leaf collimator to conform to the shape of the tumor. As the gantry rotates during the treatment fraction, the shape of the tumor, seen from the different gantry positions, will change. The multi-leaf collimator will simultaneously change accordingly to treat only the tumor and minimize the radiation dose to surrounding normal tissues as the gantry rotates around the patient. This advanced radiation treatment method is called Intensity Modulated Radiastion Therapy.

Multi-leaf collimator conformed to tumor.

Monitor display of treatment area.

This equipment is capable of up to 15 MEV and requires extreme shielding. The construction process is thorough and complex, requiring numerous calculations by certified and licensed radiation physicists and the State Certification. The LINAC vault is contructed of 7000 psi concrete. The floor of our vault is 36" plus 14" of sand and another 4-6" of floor concrete. The lid (ceiling) is 53", the primary walls are 53" and 45", the secondary walls are 20" and 28".