Osteosarcoma is the most common bone tumor in dogs that is commonly treated with amputation and intravenous chemotherapy. For some dogs, amputation may not be the most appropriate treatment option and limb-sparing treatments are sought after. Stereotactic body radiation therapy (SBRT) has been utilized to ablate tumor cells while leaving the affected limb intact and showing good primary tumor control rates. The biggest risk with using SBRT in this setting is the potential for pathologic fracture of the affected limb. To minimize risk of fracture prior to treatment, characteristics on computed tomography (CT) have been assessed to inform clinicians and owners of a percent fracture risk.

The investigators propose utilizing a dual energy CT scan to calculate bone mineral density (BMD) both before and after SBRT to assess changes that happen with treatment. The BMD measures calcium and other minerals within the bone and, theoretically, the more mineral, the denser and stronger the bone is and less likely it is to break. All patients will follow SBRT with standard of care chemotherapy and a dual energy CT three months after radiation. Additionally, the research team will serially collect bone breakdown markers before and after treatment to determine how these are correlated with the BMD and response to treatment.