A Single Institution Retrospective Comparison of Two Radiotherapy Protocols for the Palliative Treatment of Canine...

Optimal radiation protocols for canine nasal carcinoma are not established. Co-morbidities, access, and owner compliance can influence scheduling. Between 2015 and 2022, two radiotherapy protocols were used in the palliative treatment of canine nasal carcinoma at a single institution. Group A comprised 17 cases receiving 40 Gy in ten 4 Gy fractions delivered Monday, Wednesday, and Friday. Epistaxis was present in 11/17 (65%) cases. Median survival time (MST) was 298 days (95% CI: 163.54-432.45); progression-free survival was 173 days (95% CI: 117.87-228.12). Group B comprised 24 cases receiving 36 Gy in six 6 Gy fractions delivered Monday and Friday. Epistaxis was present in 20/24 (83%) cases. MST was 375 days (95% CI: 240.73-509.27); progression-free survival was 243 days (95% CI: 138.42-347.58). Dogs with Adams Stage 1 disease had the longest median overall (593 days) and progression-free survival (609 days). Four cases each received additional radiation treatment and/or toceranib at relapse. Palliative radiation therapy achieved control of clinical signs in the majority of cases, with an overall response rate of 100% (Group A) and 96% (Group B). In a multivariate Cox regression model with backwards elimination, when cases were stratified for tumor stage, neither the presence of epistaxis nor treatment (6 vs. 10 fractions) was independently associated with significant improvements in survival. Epistaxis at presentation did not appear to influence survival. These results indicate that palliative radiation therapy is highly effective in controlling clinical signs associated with nasal carcinoma. Increasing fractionation may have a limited effect on survival outcome or toxicity in the palliative setting.