IR-192 INTERSTITIAL BRACHYTHERAPY FOR EQUINE PERIOCULAR TUMORS - TREATMENT RESULTS AND PROGNOSTIC FACTORS IN 115 HORSES

One hundred and fifteen horses with periocular tumours were treated wi th iridium-192 interstitial brachytherapy. Tumours included squamous c ell carcinomas (n=52) and sarcoids (n=63). All horses were scheduled t o receive 60 Gy (minimal tumour dose) given at a low dose rate (0.034 +/- 0.010 Gy/h). The mean and median follow-up times to last contact o r death were 24 and 16 months, respectively. Chronic radiation reactio ns included palpebral fibrosis (10.4%), cataract (7.8%), keratitis and corneal ulceration (6.9%). Cosmetic changes included permanent epilat ion (21.7%) and hair dyspigmentation (78.3%). The one year progression -free survival (PFS) rates for sarcoids and carcinomas were 86.6% and 81.8% and the 5 year PFS rates were 74.0% and 63.5%, respectively. The horse age and sex, histopathological type, anatomical subsite and cla ssification (WHO T1-3) were included in the analysis of prognostic fac tors. The only significant prognostic factor that independently affect ed PFS time was the WHO T-classification (P=0.009, relative risk=0.85) . When compared to horses with T1 lesions, horses with T2 and T3 lesio ns had 1.8-fold and 3.4-fold increased risks, respectively, for tumour recurrence (relative excess risk). The one year PFS rates for T1, T2 and T3 lesions were 95.2%, 89.5% and 66.2%, respectively. The 5 year P FS rates were 72.2%, 74.0% and 53.1%, respectively. The results of thi s study indicate that irradiation is an effective treatment option for horses with T1-2 lesions and should be part of a combined treatment m odality for horses with T3 lesions.