Evaluating Feline Release Criteria Following 131 I Therapy for Hyperthyroidism.

Area of Science:

• Veterinary Medicine
• Endocrinology
• Radiological Health

Background:

• Hyperthyroidism is a common endocrine disorder in cats, often treated with radioactive iodine (131I) ablation.
• Post-treatment, cats become a radiation source, necessitating release criteria to minimize risks to owners.
• Current veterinary release criteria for hyperthyroid cats are significantly more restrictive than those in human medicine, leading to prolonged hospitalization.

Purpose of the Study:

• To evaluate the administered activities and exposure rates in hyperthyroid cats treated with 131I at LSU Veterinary Teaching Hospital.
• To determine if current veterinary release criteria for hyperthyroid cats are overly restrictive.
• To assess the potential radiological risk to cat owners by measuring radioactivity and calculating total effective dose equivalents.

Main Methods:

• Measurement of administered 131I activities and exposure rates in hyperthyroid cats.
• Radioassays on cat surfaces, excreta, and environment to quantify residual radioactivity.
• Calculation of annual total effective dose equivalents (TEDE) to cat owners using Nuclear Regulatory Commission (NRC) guidelines (Regulatory Guide 8.39 Revision 1).

Main Results:

• Minimal radioactivity was detected on cats and their environment post-treatment.
• Calculated TEDE for cat owners was unlikely to exceed 1 mSv.
• The study indicates that most hyperthyroid cats could be safely discharged on the same day as their 131I injection.

Conclusions:

• Current veterinary release criteria for hyperthyroid cats treated with radioactive iodine are likely overly conservative.
• Same-day discharge for hyperthyroid cats is feasible, minimizing the burden on owners, veterinary staff, and the animal.
• Revising veterinary release criteria could align with human medicine standards, improving patient and owner convenience without compromising safety.