A simple visual score of heterogeneity of FDG uptake as prognostic marker in sarcoma patients

Objectives
Spatial heterogeneity of FDG uptake in the tumor is a promising predictor of patient outcome in various tumor entities. Different definitions have been proposed for spatial heterogeneity of tracer uptake and mathematical approaches range from simple to very sophisticated algorithms. Here we propose a simple score for visual assessment of both heterogeneity (VSHETER) and shape irregularity (VSIRREG) of FDG uptake in the primary tumor. The prognostic value of these new scores was evaluated in sarcoma patients with F18‐FDG‐PET for initial staging.
Methods
In total 56 sarcoma patients (30 m, median age 15 y, range 2‐61 y) were included retrospectively. Histological subtypes were 22 Ewing sarcomas (EWS), 17 osteosarcomas (OS) and 17 sarcomas with various subtypes (VS). Primary tumors were visually analyzed for maximum tracer uptake relative to the liver uptake (5‐score), size (3‐score), heterogeneity of FDG uptake (3‐score), irregularity of the shape of FDG uptake (3‐score) and central necrosis (yes/no). The presence or absence of metastases was also taken into account (yes/no). The metabolic tumor volume (MTV) was measured using the semi‐automatic ROVER 3D segmentation tool which is based on thresholding at the volume‐reproducible intensity threshold after subtraction of the local background. Cox proportional hazards models and corresponding hazard ratios (HR) were used to analyze the predictive value of the visual scores as well as SUVmax and MTV for overall survival (OAS) and progression free survival (PFS).
Results
40 patients (17 EWS, 15 OS, 8 VS) survived till the end of the follow‐up with OAS times ranging from 9.1 to 97.8 months (median 46.5 months). OAS of non‐survivors ranged from 2.7 to 49.6 months (median 17.1 months). A significant association with sarcoma subtype was observed for SUVmax (p<0.01), VSHETER (p=0.05) and central necrosis (p<0.01). Multivariate cox proportional hazard analysis revealed VSHETER (HR=2.4, p=0.01) and tumor subtype (VS vs EWS, HR=4.9, p<0.01) as significant predictors of PFS whereas there was no significant association of PFS with VSIRREG, central necrosis, presence of metastatses, SUVmax or MTV. OAS was associated with the presence of metastases (HR=5.1, p=0.01), VSHETER (HR=2.6, p=0.04) and tumor subtype (VS vs EWS, HR=3.2, p=0.05). Conclusion A simple visual 3‐score for heterogeneity of FDG uptake in the primary tumor provides additional power for the prognosis of sarcoma patients based on F18‐FDG‐PET. Simple visual scores are easily implemented in the routine clinical workflow.