LAUSR

The purpose of this bi-institutional retrospective study was to determine whether survival for dogs with extremity osteosarcoma is improved through the use of stereotactic radiotherapy (SRT; a single fraction of 25 Gy, or 36 Gy total given in 3 consecutive daily fractions) plus chemotherapy, versus lower dose conventionally planned and delivered hypofractionated radiotherapy (CHRT; 14-20 Gy total in 1-2 consecutive daily fractions) plus chemotherapy. We also sought to determine whether baseline pain severity influences oncologic outcomes following radiotherapy for canine extremity osteosarcoma. The medical records of 82 dogs undergoing radiotherapy for confirmed or presumed osteosarcoma were reviewed. In dogs receiving combinations of both chemotherapy and radiotherapy, survival was significantly longer with SRT vs. CHRT (median overall survival time: 350 vs. 147 days; p = 0.031). In a univariate analysis, dogs with pulmonary metastases and high pain at the time of irradiation had short overall survival times; use of high radiation doses and chemotherapy were associated with improved survival. Separate multivariable models were built to assess the predictive nature of various factors that might influence event-free or overall survival in dogs treated with radiotherapy, with or without chemotherapy; for dogs treated with both chemotherapy and radiotherapy, overall survival times were significantly longer when baseline pain scores were "low" (vs. "high"; hazard ratio: 0.258; p = 0.030), radiation doses were high (hazard ratio: 0.943; p = 0.034). Neither pain nor radiation dose were associated with survival in dogs treated with radiotherapy, without chemotherapy. This article is protected by copyright. All rights reserved.