18 F-FDG PET/CT Derived Volumetric Parameters Can Predict Outcome in Pediatric Ewing Sarcoma

OBJECTIVE: To evaluate the prognostic and predictive value of metabolic and volumetric parameters obtained from baseline (PET1) and post-chemotherapy (PET2) 18 F-FDG PET/CT in pediatric Ewing sarcoma (EWS) patients, focusing on their associations with histopathologic response, metastatic presentation, overall survival (OS), and progression-free survival (PFS). METHODS: This retrospective single tertiary academic center study included 55 pediatric EWS patients who underwent PET1. Twenty-four patients also had PET2. SUVmax, SUVpeak, metabolic tumor volume (MTV), total lesion glycolysis (TLG) and their percentage changes (∆) between PET scans were calculated using absolute (SUV 2.0 and 2.5) and relative (40% and 45%) thresholds. Anatomic tumor volume was also measured. Histopathologic evaluation was available for 40 patients with PET1 and 18 patients with PET2. Associations were analyzed using logistic and Cox regression models. RESULTS: Baseline metabolic and volumetric PET parameters were significantly higher in patients with presenting metastasis. Among these, TLG (45%) was identified as the only independent predictor of metastatic presentation (OR = 1.026, p = 0.019). Baseline MTV (2.0) was independently associated with shorter OS (HR = 1.026, p = 0.003) and PFS (HR = 1.035, p = 0.038). Combined stratification using MTV (2.0) and histologic response revealed that patients with an unfavorable histologic response but low MTV demonstrated superior OS and PFS rates than those with an unfavorable response and high MTV. The survival outcomes of patients with a favorable histologic response and high MTV were comparable to those with an unfavorable response and low MTV. However, PET parameters did not reliably predict histopathologic response in this cohort. CONCLUSIONS: Baseline MTV (2.0) demonstrated prognostic value for OS and PFS, while TLG (45%) independently predicted metastatic presentation in pediatric EWS. The combination of MTV (2.0) and histologic response appears to provide complementary prognostic information. Prospective, multicenter studies with standardized imaging and treatment protocols are warranted to validate the role of volumetric 18 F-FDG PET parameters in clinical risk stratification.