Prospective pilot study utilizing changes in quantitative values obtained on serial fluorine‐18 fluorodeoxyglucose (18F‐FDG) positron emission tomography–computed tomography (PET/CT) in dogs with appendicular osteosarcoma before and after stereotactic body radiation therapy (SBRT) and carboplatin chemotherapy to assess for prediction of survival and therapeutic effectiveness

Serial fluorine 18 fluorodeoxyglucose (18F‐FDG) positron emission tomography–CT (PET/CT) is commonly used in human oncology to prognosticate and evaluate for therapeutic effectiveness. In this pilot study, dogs with naturally occurring appendicular osteosarcoma were evaluated with serial 18F‐FDG PET/CT in an attempt to assess for response to therapy, prognostic factors, and appropriateness of imaging intervals. Fourteen dogs were enrolled in the trial. All dogs had the initial 18F‐FDG PET/CT (PET1), with nine dogs having their end‐of‐therapy 18F‐FDG PET/CT (EoT PET) 3 months after stereotactic body radiation therapy (SBRT) to the primary tumor. The median percent change from the PET1 to the EoT PET for the standard uptake value maximum (SUVmax%) was −58% (range: −17 to −88%), metabolic tumor volume (MTV%) was −99.8% (range: −65 to −100%), and total lesion glycolysis (TLG%) was −99.8% (range: −75 to −100%), all of which were significant (P < .05, <.05, and <.05, respectively). On evaluation, it was found that volumes of GTV and CTV were significant for survival (P < .05 and <.05), MTV1, TLG1, and SUVmax on the EoT PET (SUVmaxEoT) were predictive of metastasis (P < .05), and the SUVmax% was significantly correlated to the time to first event (P < .05). Based on this data, serial 18F‐FDG PET/CT performed 3 months after SBRT can show a significant reduction in avidity, and the quantitative data collected may help predict metastatic disease in canine appendicular osteosarcoma.