Use of the <scp>IlluminOss</scp> Photodynamic Bone Stabilisation System Following Stereotactic Body Radiation Therapy for Limb‐Sparing in Six Dogs With Presumptive Appendicular Osteosarcoma

Osteosarcoma is the most common primary bone tumour in dogs, with approximately 75% of cases occurring in the appendicular skeleton. Standard-of-care therapy consists of limb amputation followed by carboplatin chemotherapy. A minority of dogs have limb-sparing treatments including stereotactic body radiation therapy (SBRT) or surgery. SBRT has a high incidence of pathologic fracture (41%-80% of cases) following treatment, which often results in amputation or euthanasia. Prophylactic bone stabilisation following SBRT has not been recommended due to high complication rates. The IlluminOss system (IS) is an intramedullary implant consisting of a light-curable polymer within an inflatable balloon catheter, which is approved in humans for traumatic fractures and prevention of fractures secondary to bone metastases. We performed a study to assess the safety and feasibility of using the IS following SBRT in six dogs with suspected appendicular osteosarcoma. The IS was placed the day after completion of SBRT. Five of six dogs received adjuvant carboplatin chemotherapy. The IS was well tolerated with no implant-associated infections or immediate post-operative complications occurring. Pathologic fractures occurred in four dogs with a median fracture-free interval of 107 days. Three dogs ultimately underwent amputation due to pathologic fractures. No other post-operative complications occurred. The median survival time was 156 days. These findings suggest that the IS may be a palliative option for dogs following SBRT, but further research to optimise use in the dog and evaluation of the use of the IS with ancillary fixation is necessary.