Thyroid Treatment Using Radiotherapy in Cats 💉🐱

By Dr Duncan Houston, BVSc

In 2025, radioactive iodine therapy (I‑131) remains the gold standard for curing feline hyperthyroidism. It's safe, effective, and minimally invasive. In this expert guide, Dr Duncan Houston explains the process, pros and cons, preparation, and post-treatment care. 🧪

🔬 What Is Radiotherapy for Hyperthyroid Cats?

Hyperthyroid cats produce excessive thyroid hormone due to benign thyroid tumors. I‑131 is a radioactive form of iodine that selectively destroys abnormal thyroid tissue—curing the disease without surgery or long-term medications. 🧬

🧪 How It Works

Thyroid cells naturally absorb iodine. When I‑131 is injected under the skin (like a vaccine), it’s taken up by the overactive thyroid cells. Inside the thyroid, the radioactive iodine emits high-speed electrons that destroy the tumor tissue from within, sparing the rest of the body. Only the thyroid is affected. 🔬⚡

🏥 The Treatment Process

1. 📋 Initial consultation with lab work, T4 testing, and kidney function screening.
2. 📸 Optional pertechnetate scan to assess thyroid mass and help calculate dose.
3. 💉 Subcutaneous I‑131 injection is administered—no anesthesia needed.
4. 🏨 3–7 days of isolation in a treatment facility while radiation dissipates.
5. 🏡 After discharge, a short confinement period (7–14 days) at home is required.
6. 📊 Follow-up bloodwork is performed at 1 and 3 months to confirm recovery.

📸 Pertechnetate Scan: What It Reveals

This optional scan maps the thyroid’s size, activity, and distribution. It’s used to:

• ✅ Confirm diagnosis
• 🧠 Identify if both glands are affected
• ⚠️ Detect ectopic (misplaced) or malignant thyroid tissue
• 📏 Determine the right dose of I‑131

Skipping the scan lowers treatment cost but increases risks of under- or over-treatment. It’s especially useful if malignancy is suspected. 📉

✅ Advantages of I‑131 Therapy

• 💯 Curative in 95–98% of cases—no daily pills or future surgeries needed
• 💉 No anesthesia required—ideal for senior or cardiac-compromised cats
• ⏱️ Quick treatment—one injection + brief boarding
• 😺 Low stress for cats, minimal handling
• 🛡️ Targeted safety—healthy tissues are unaffected
• 📈 Improves quality of life quickly—often within weeks

⚠️ Disadvantages & Limitations

• ⛔ Temporary separation from pet parent due to radiation
• 🚫 Close human contact restricted post-treatment (especially kids & pregnant women)
• 💰 Higher upfront cost compared to medication
• 🧪 Follow-up testing still required (1–3 months)
• 🧻 Use of special flushable litter needed post-treatment
• ❗ May unmask kidney disease once thyroid hormone levels normalize

👨‍⚕️ Kidney Screening Is Critical

Untreated hyperthyroidism boosts kidney filtration. Once thyroid hormone levels are restored, underlying kidney disease can surface. Screening before I‑131 is essential. If risks are found, a trial with methimazole may be recommended first. 🧪💧

📍 Post-Treatment: What to Expect

• 📆 7–14 days home confinement with reduced contact
• 🧼 Use of flushable litter only—no clay or clumping
• 🥼 No contact with immunocompromised persons during this time
• 🩺 T4 and kidney rechecks at 1 and 3 months
• ❄️ Some cats may become hypothyroid post-treatment (less than 5%)

🧑‍⚕️ When Is I‑131 Not Ideal?

• ❌ Confirmed or suspected severe kidney disease
• ❌ Cat cannot tolerate isolation/quarantine
• ❌ Owners unable to comply with post-treatment restrictions

🌍 Facility Access & Referrals

I‑131 treatment is not available at regular clinics. Your veterinarian will refer you to a specialty center. These facilities are licensed and regulated for safe radioactive handling. 📍

📱 Ask A Vet App Support

Before, during, or after I‑131 therapy, the Ask A Vet app gives you peace of mind:

• 🧪 Pre-treatment lab interpretation
• 📋 Therapy planning and referral questions
• 📤 Upload scans or recheck results
• 💬 24/7 Q&A with licensed vets

🏁 Final Takeaway

Radioiodine (I‑131) therapy is the most definitive, safe, and effective cure for feline hyperthyroidism in 2025. With proper screening and follow-up, most cats make a full and lasting recovery—no more pills, no more hormone swings, just better quality of life. 🐱❤️

For support at every step of the journey, download the Ask A Vet app. Your cat’s healthiest future starts today. 🩺✨