18F-FDG PET SUVmax correlates with osteosarcoma histologic response to neoadjuvant chemotherapy: preclinical evaluation in an orthotopic rat model.

UNLABELLED: Assessment of osteosarcoma response to neoadjuvant chemotherapy is performed by histopathologic analysis after surgical resection of the primary tumor. The purpose of this study was to evaluate whether (18)F-FDG PET could be a noninvasive surrogate to histopathologic analysis and allow for earlier response evaluation to neoadjuvant chemotherapy in osteosarcoma. METHODS: Metabolic response to neoadjuvant chemotherapy was assessed in immunocompetent rats with a preestablished orthotopic osteosarcoma using (18)F-FDG PET before and after receiving 2 doses of ifosfamide. Comparison was then made by assessing histologic responses on euthanized animals. RESULTS: Maximum standardized uptake value (SUVmax) measured by (18)F-FDG PET after 2 doses of chemotherapy was correlated to histologic classification (P < 0.01). An SUVmax less than 15 corresponded to good responders, whereas an SUVmax greater than 15 but less than 20 and an SUVmax greater than 20 corresponded to partial responders or nonresponders, respectively. A 40% decrease in SUVmax between the first and second (18)F-FDG PET scans distinguished between partial and good response to chemotherapy. CONCLUSION: Determination of SUVmax using semiquantitative (18)F-FDG PET predicts response to neoadjuvant chemotherapy earlier than does histologic analysis.