Factors influencing survival after radiotherapy of nasal tumors in 130 dogs

Improvements in survival of dogs with nasal tumors have been slow to develo p throughout the past three decades. Despite multiple studies examining var ious radiation time-dose schema, the advancement of CT-based computerized t reatment planning, and the evaluation of detailed staging systems, the opti mal treatment regimen, and most important prognostic factors regarding surv ival remain unclear. In this study, data from four previous studies were co mbined with data from 44 additional dogs, and this population of 130 dogs w as evaluated for factors which influenced survival. Twenty-one dogs were tr eated with orthovoltage at the University of Pennsylvania. One hundred nine dogs were treated with cobalt photons at North Carolina State University. Sixty-five of these 109 dogs had been previously described. Of the 44 dogs not previously described, 35 were treated with a shrinking field technique. Survival was determined from the medical record, or from information deriv ed by telephone or mail survey. The univariate Cox regression model was use d to examine for relationship between various patient, tumor, and treatment variables and survival. Significant relationships identified in the univar iate analysis were further analyzed using the multivariate Cox regression m odel. Median survival of the 130 dogs was 8.9 months (95% C.I., 8-11 months ). In the univariate analysis, the following variables were associated with decreased survival: 1) age >10 years old, 2) regional lymph node metastasi s, 3) advanced tumor stage, 4) use of megavoltage radiation, 5) overall tot al dose >55 Gray, and 6) boost technique performed. In a multivariate analy sis of 125 dogs with complete data for age, radiation type, and radiation d ose, age (p < .001) and radiation type (p = .02) were identified as joint p redictors of survival. After adjusting for age, the staging system lost pro gnostic significance (p = .06). In a subset of dogs that received cobalt ra diation, after adjusting for age, dogs treated with a boost technique had d ecreased survival (p = .001). In general, local control of canine nasal tum ors following aggressive radiation therapy is poor. Early diagnosis and sel ection of appropriate patients is warranted and palliative types of treatme nt should be considered in dogs with a poor chance of long term survival.