EFFICACY OF COBALT-60 RADIOTHERAPY IN DOGS WITH PITUITARY-DEPENDENT HYPERADRENOCORTICISM

Objective-To determine efficacy of cobalt 60 radiotherapy in dogs with pituitary-dependent hyperadrenocorticism (PDH) that have detectable t umors but no neurologic abnormalities. Design-Case series. Animals-6 d ogs with PDH that had a detectable pituitary mass an magnetic resonanc e images. Procedure-Radiation was delivered in 11 fractions during a 3 .5-week period for a total dose of 44 Gy. Clinical signs were evaluate d, a urinalysis and ACTH stimulation test were performed, and urine co rtisol-to-creatinine ratio and plasma endogenous ACTH concentration we re measured before, immediately after, and 1, 3, 6, 9, and 12 months a fter radiotherapy. Magnetic resonance imaging was repeated 1 year afte r radiotherapy. Results-Clinical signs of hyperadrenocorticism resolve d in 3 dogs but recurred in 2 of the 3, Clinical condition of 2 dogs i mproved but did not return to normal. One dog did not improve. Results of ACTH stimulation tests and urine cortisol-to-creatinine ratios cor related with clinical signs. Plasma endogenous ACTH concentration tran siently decreased in all 6 dogs, One year after radiotherapy size of t umors was decreased by 25% in 2 dogs; in the other 4 dogs, tumors coul d no longer be detected. None of the dogs developed neurologic abnorma lities. Adverse effects of radiotherapy were mild. Clinical Implicatio ns-Radiotherapy did not result in adequate control of clinical signs o f hyperadrenocorticism in 5 of 6 dogs, but size of pituitary tumors wa s dramatically reduced. Thus, it may be reasonable to recommend radiot herapy in dogs with PDH that have pituitary tumors for which greatest vertical height is 8 mm or more.