Retrospective study of orthovoltage radiation therapy for nasal tumors in 42 dogs

Megavoltage radiation therapy currently is the standard of care for dogs wi th nasal tumors. Some studies report that surgery and adjunctive orthovolta ge radiation therapy result in longer control of these tumors than does meg avoltage radiation therapy alone. This study reports less effective control of nasal tumors in dogs treated with surgery and orthovoltage radiation th an previously observed, supporting the superiority of megavoltage radiation therapy for these tumors. In addition, this study suggests 2 new prognosti c indicators for dogs with nasal rumors and describes toxicity associated w ith surgery and orthovoltage therapy. Forty two dogs with nasal rumors were treated with surgical cytoreduction and 48 Gy orthovoltage radiation thera py administered in twelve 4-Gy fractions. Median survival was 7.4 months. O ne- and 2-year survival rates were 37% and 17% respectively. Dogs with faci al deformity had shorter survival than those without deformity (P = .005). Dogs with resolution of clinical signs after treatment had longer survival than those with chronic nasal signs (P = .0001). Acute radiation toxicity w as moderate to severe for skin and eye and negligible for oral mucosa. Toxi city healed within 1 month after radiation therapy. Late toxicity was mild, but 70% of evaluable dogs experienced persistent ocular signs. Only 39% of dogs achieved a disease-free period.