Stereotactic radiation therapy for the treatment of functional pituitary adenomas associated with feline acromegaly

BACKGROUND: Conventional fractionated radiotherapy has been shown to be partially effective for management of pituitary tumors in cats that cause acromegaly and diabetes mellitus (DM), but, the efficacy and safety of stereotactic radiation therapy (SRT) as a treatment for acromegalic cats has not been described. HYPOTHESIS: Stereotactic radiation therapy is an effective and safe treatment for controlling acromegaly associated with pituitary adenomas in cats. Additionally, SRT‐treated acromegalic cats with DM will experience a decrease in insulin requirements after radiation therapy. ANIMALS: Fifty‐three client‐owned cats referred to Colorado State University for SRT to treat pituitary tumors causing poorly controlled DM secondary to acromegaly. METHODS: Retrospective study of cats treated for acromegaly with SRT between 2008 and 2016 at Colorado State University. Diagnosis of acromegaly was based on history, physical examination, laboratory results, and cross‐sectional imaging of the pituitary. Signalment, radiation protocol, insulin requirements over time, adverse effects, and survival were recorded. RESULTS: Median survival time was 1072 days. Of the 41 cats for which insulin dosage information was available, 95% (39/41) experienced a decrease in required insulin dose, with 32% (13/41) achieving diabetic remission. Remission was permanent in 62% (8/13) and temporary in 38% (5/13) cats. Median duration to lowest insulin dose was 9.5 months. Of the treated cats, 14% developed hypothyroidism and required supplementation after SRT. CONCLUSIONS: Stereotactic radiation therapy is safe and effective for treating cats with acromegaly. Cats treated with SRT have improved survival time and control of their DM when compared to previously reported patients treated with non‐SRT.