MEGAVOLTAGE IRRADIATION OF NEOPLASMS OF THE NASAL AND PARANASAL CAVITIES IN 77 DOGS

Seventy-seven dogs with malignant tumors of the nasal and paranasal ca vities were treated by use of radiotherapy. The tumors included carcin omas (58) and sarcomas (19). Radiographic findings, including site of involvement and tumor extension, were the basis of clinical staging. S taging was performed according to the tumor, node, metastasis staging of the World Health Organization, and a modified staging scheme based on prognostic factors that seemed to correlate best with response to t reatment. All irradiations were done with a telecobalt 60 unit. Fifty- six dogs were treated with irradiation alone, and 21 had partial tumor resection prior to radiotherapy. Treatment dose was 48 Gy (minimal tu mor dose) administered on a Monday-Wednesday-Friday basis at 4 Gy/frac tion over 4 weeks. The irradiation technique emphasized rostral field with a generous treatment volume. Duration of follow-up after irradiat ion ranged from 1 month to 61 months. The 1- and 2-year overall surviv al rates were 60.3% and 25%, respectively, and the 1- and 2-year relap se-free survival rates were 38.2% and 17.6%, respectively. Results of histologic examination and our modified staging scheme were significan t (P = 0.02 and P = 0.04, respectively) prognostic factors of relapse- free survival. Conversely, tumor site, tumor extension, World Health O rganization clinical stage, and cytoreductive surgery prior to irradia tion did not affect the outcome of treatment. According to our modifie d staging scheme, dogs with stage-2 disease have a poorer prognosis th an dogs with stage-1 disease, with a relative risk of relapse 2.3-fold higher. Dogs with carcinoma had a poorer prognosis than dogs with sar coma (predominantly chondrosarcoma) with a relative risk of relapse 3. 3-fold higher. Furthermore, dogs with chondrosarcomas fared significan tly (P = 0.05) better than those with adenocarcinomas. Most acute radi ation reactions were acceptable. Chronic ocular complications were see n in 45% (35/77) of the dogs.