Mise au point et validation d’un fantôme spécifique pour assurer le suivi des mesures quantitatives en tomographie par émission de positons

Abstract

Standardized uptake values (SUV) are widely used in positron emission tomography (PET) to quantify [18F]2-fluoro-2-deoxy- d-glucose (18F-FDG) uptake, particularly in therapeutic follow-up. However, this index depends on many factors, be they methodological or biological, and its use is still a subject of debate. In this context, it is fundamental to establish a regular quality control to ensure quantitative indices constancy. In this perspective, a specific phantom with different size cylinder-shaped inserts was developed. The purpose of this study is to show the sensitivity and the interest of this phantom. Methods The phantom sensitivity was studied through SUV and recovery coefficient (RC) measurements. Several data analysis methods based on region of interest definition (ROI) were used. Data were reconstructed using clinical routine algorithms. We studied RC variation using cylinders with relative change of size and uptake (simulating treatment response) for different tumor-to-background activity ratio (TBR). Subsequently, the phantom was tested on another PET scanner. Results For all data analysis methods, a considerable RC variation, of about 50%, was found with cylinder size. Measurement methods based on isocontours showed a strong correlation. This phantom also allowed to measure a relative uptake change which turned out to be independent of the measurement method. Despite calibration of the PET/CT systems, quantification differences of about 20% remained between the two centers studied. Conclusion The results obtained show the interest of this phantom in the framework of following-up quantitative measurements in a given institution, or of an intercomparison in multicenter studies.