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Radioactive Iodine Therapy
Radioactive iodine (I-131) therapy is the gold standard treatment for feline hyperthyroidism. It cures the disease by destroying overactive thyroid tissue with targeted radiation while sparing normal tissue.
Key Facts
- Single injection of iodine-131 given under the skin; curative in 96-98% of cats
- Iodine attaches selectively to thyroid tissue; emitted beta particles destroy only the tumor
- Cat must be quarantined at the facility for 3-7 days until radiation levels drop
- Home restrictions for ~10 days after release: confined indoors, flushable litter, limited human contact
- Children and pregnant women must avoid the cat during this period
- Pertechnetate scan before treatment identifies tumor extent, guides dosing, detects malignancy (3-5%)
- Skipping the scan risks under- or overdosing and missing cancer
- Less than 5% of cats become hypothyroid afterward (requiring thyroid supplementation)
- Not recommended for cats with poor kidney function until kidney status is evaluated
- Also used for canine thyroid carcinoma at much higher doses
- Species: cats (primarily); dogs (for thyroid carcinoma)