Prospective pilot study utilizing changes in quantitative values obtained on serial fluorine-18 fluorodeoxyglucose ( 18 F-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 ( 18 F-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 18 F-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 18 F-FDG PET/CT (PET1), with nine dogs having their end-of-therapy 18 F-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 (SUV max% ) 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), MTV 1 , TLG 1 , and SUV max on the EoT PET (SUV maxEoT ) were predictive of metastasis (P < .05), and the SUV max% was significantly correlated to the time to first event (P < .05). Based on this data, serial 18 F-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.