Some thyroid drugs contain radioactive iodine

Radiation Oncology and Nuclear Medicine

Department / University Clinic for Small Animals and Horses

Overactive thyroid gland (hyperthyroidism) in cats is a condition that affects elderly patients in particular and leads to weight loss, increased appetite, vomiting, diarrhea, high blood pressure and other symptoms. Therapy is absolutely necessary, as in chronic illnesses without therapy additional heart and kidney problems occur and the patient can die.
An overactive thyroid can be treated either with regular medication, surgical removal, or irradiation of the affected thyroid. The most effective therapy for this disease is radioiodine therapy. In doing so, the cat becomes radioactive 131Iodine is administered, which the body treats like normal iodine and is only stored in the thyroid gland. It accumulates in overactive thyroid areas 131Iodine increases, which leads to intensive local irradiation of the diseased parts of the thyroid with beta radiation (particle radiation). Beta radiation only has a very limited range in the body. This achieves a maximum radiation effect on the diseased tissue while protecting the healthy areas and the environment. This enables normalization of thyroid function in around 95% of patients. Because of the gamma radiation that is also emitted, there is also radiation exposure of the environment after administration (in contrast to beta radiation, gamma radiation penetrates the body). This does not represent a greater burden for the patient than a computed tomography, but the people living with the patient must not be exposed to any unnecessary additional radiation. Therefore the patients have to stay in the animal hospital for about 5 days after the therapy.