What and how should we measure in paediatric oncology FDG-PET/CT? Comparison of commonly used SUV metrics for differentiation between paediatric tumours

BACKGROUND: In clinical routine, SUV(max) and SUV(peak) are most often used to determine the glucose metabolism in tumours by (18)F-FDG PET/CT. Both metrics can be further normalised to SUVs in reference regions resulting in a SUV ratio (SUV(ratio)). The aim of the study was to directly compare several widely used SUVs/SUV(ratios) with regard to differentiation between common tumours in paediatric patients; a special focus was put on characteristics of reference region SUVs. METHODS: The final study population consisted of 61 children and adolescents with diagnoses of non-Hodgkin lymphoma (NHL, n = 25), Hodgkin lymphoma (HL, n = 14), and sarcoma (n = 22). SUV metrics included SUV(max) and SUV(peak) as well as both parameters normalised to liver and mediastinal blood pool, respectively, yielding the SUV(ratios) SUV(max/liver), SUV(max/mediastinum), SUV(peak/liver), and SUV(peak/mediastinum). RESULTS: The metrics SUV(max), SUV(peak), SUV(max/liver), and SUV(peak/liver) all proved to be sensitive for tumour differentiation (p ≤ 0.008); in contrast, SUV(max/mediastinum) and SUV(peak/mediastinum) revealed to be non-sensitive approaches. Correlation analyses showed inverse associations between reference region SUVs and SUV(ratios) (p < 0.05). Multiple regression analyses demonstrated significant effects of factors as bodyweight and uptake time on reference region SUVs (p < 0.01), and thus indirectly on the corresponding SUV(ratios). CONCLUSIONS: In the paediatric population, the ability to differentiate between common tumours remarkably varies between SUV metrics. When using SUV(ratios), the choice of reference region is crucial. Factors potentially influencing reference region SUVs (and thus SUV(ratios)) should be taken into account in order to avoid erroneous conclusions. When not possible, SUV(max) and SUV(peak) represent less complex, more robust alternatives.