Prognostic value of 18F-FDG PET/CT derived metabolic parameters in pediatric osteosarcoma.
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OBJECTIVE: To investigate whether metabolic and volumetric 18F-FDG PET parameters are associated with histopathological response, metastatic disease at diagnosis, overall survival (OS), and progression-free survival (PFS) in pediatric osteosarcoma (OST) patients. Additionally, to compare absolute and relative threshold methods for metabolic tumor volume (MTV) calculation. METHODS: This single-center retrospective study included 26 pediatric OST patients who underwent 18F-FDG PET/CT at diagnosis and, when available, after neoadjuvant chemotherapy. SUVmax, SUVpeak, MTV, total lesion glycolysis (TLG) and anatomic tumor volume of the primary tumor, along with whole-body MTV (wb-MTV) and whole-body TLG encompassing all FDG-avid metastatic lesions, were measured and their percentage changes (∆) between PET scans were calculated. MTV and TLG were calculated using absolute (SUV 2.0) and relative (40% of tumor SUVmax) threshold methods. RESULTS: Baseline 18F-FDG PET parameters did not predict histopathological response. But, we found that ΔSUVmax, ΔMTV (2.0), ΔTLG (2.0), and ΔTLG (40%) were associated with histopathological response (p = 0.029). Although not statistically significant, patients with metastases had higher baseline SUVmax, SUVpeak, MTV (2.0), and TLG (2.0) values. Anatomic tumor volume did not differ between the metastatic and localized groups. Patients with wb-MTV (40%) > 137.5 had a significantly higher mortality risk (HR = 4.27, p = 0.017). Kaplan-Meier analysis revealed that patients with primary tumors exhibiting SUVmax > 5.56 and SUVpeak > 4.57 had significantly lower estimated 5-year OS rates (p = 0.036 and 0.029), even after excluding patients with metastasis at diagnosis. CONCLUSIONS: ΔSUVmax, ΔMTV (2.0), ΔTLG (2.0), and ΔTLG (40%) were found to be associated with histopathologic response, suggesting that these changes may serve as predictors of histopathologic outcome. MTV (2.0) may be a more reliable indicator of tumor aggressiveness than anatomic tumor volume, as it tended to be higher in the metastatic group. Our finding suggests that using absolute threshold may better reflect tumor burden in primary lesions with high metabolic activity, whereas relative threshold may be more suitable for evaluating total tumor burden, including low 18F-FDG uptake metastases. Inferior survival outcome is associated with elevated baseline SUVmax and SUVpeak values persisted even when patients with metastatic disease were excluded, suggesting their potential prognostic value.