Outcome of 9 dogs treated with stereotactic radiation therapy for primary or metastatic vertebral osteosarcoma.

Primary and metastatic vertebral osteosarcoma (OSA) in the dog carries an overall guarded prognosis. Previously reported definitive treatments in dogs with vertebral OSA have included surgery, radiotherapy, chemotherapy or a combination of those therapies. This retrospective study was completed to determine patterns of failure, duration of local control and survival time in dogs with vertebral OSA treated with stereotactic radiation therapy (SRT). Nine dogs were treated with SRT for vertebral OSA. Protocols ranged from 1 to 5 fractions with total prescription ranging from 13.5 to 36 Gy. Six dogs had primary lesions and 3 had metastatic lesions. Neurologic score improved in 4 patients, remained the same in 4 and worsened in 1. Five of the 6 dogs that presented with assessable spinal pain had reported improvement in pain. Overall median survival time was 139 days and median duration of pain control was 77 days. There was not a statistically significant survival difference between dogs presenting with primary or metastatic disease, or dogs that had improvement in neurologic score following SRT. The data suggests similar survival times to the previously reported definitive treatments in dogs with vertebral OSA and displays continued difficulty in controlling this tumour. The dose limiting structure is the late responding spinal cord, but many of the patients herein died prior to the expected time to development of late radiation side effects.