title: Iridium-192 interstitial brachytherapy for equine periocular tumours: treatment results and prognostic factors in 115 horses.
abstract: One hundred and fifteen horses with periocular tumours were treated with iridium-192 interstitial brachytherapy. Tumours included squamous cell carcinomas (n = 52) and sarcoids (n = 63). All horses were scheduled to 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 or death were 24 and 16 months, respectively. Chronic radiation reactions included palpebral fibrosis (10.4%), cataract (7.8%), keratitis and corneal ulceration (6.9%). Cosmetic changes included permanent epilation (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 classification (WHO T1-3) were included in the analysis of prognostic factors. The only significant prognostic factor that independently affected 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 lesions 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 PFS rates were 72.2%, 74.0% and 53.1%, respectively. The results of this study indicate that irradiation is an effective treatment option for horses with T1-2 lesions and should be part of a combined treatment modality for horses with T3 lesions.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis 95616-8745, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Théon
authors.forename: J R
authors.initials: JR
authors.lastname: Pascoe
mesh_terms: D000818:Animals; D001918:Brachytherapy / Q000662:veterinary*; D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy / Q000662:veterinary*; D005128:Eye Diseases / Q000532:radiotherapy / Q000662:veterinary; D005134:Eye Neoplasms / Q000532:radiotherapy / Q000662:veterinary*; D006734:Horse Diseases / Q000532:radiotherapy*; D006736:Horses; D007496:Iridium Radioisotopes / Q000009:adverse effects / Q000627:therapeutic use*; D011379:Prognosis; D012507:Sarcoidosis / Q000532:radiotherapy / Q000662:veterinary*
chemical_list: D007496:Iridium Radioisotopes