Abstract
BackgroundThe current de facto standard for quantification of tumor metabolism in oncological whole-body PET is the standardized uptake value (SUV) approach. SUV determination requires accurate scanner calibration. Residual inaccuracies of the calibration lead to biased SUV values. Especially, this can adversely affect multicenter trials where it is difficult to ensure reliable cross-calibration across participating sites. The goal of the present work was the evaluation of a new method for monitoring scanner calibration utilizing the image-derived arterial blood SUV (BSUV) averaged over a sufficiently large number of whole-body FDG-PET investigations.Data of 681 patients from three sites which underwent routine 18F-FDG PET/CT or PET/MR were retrospectively analyzed. BSUV was determined in the descending aorta using a three-dimensional ROI concentric to the aorta’s centerline. The ROI was delineated in the CT or MRI images and transferred to the PET images. A minimum ROI volume of 5 mL and a concentric safety margin to the aortic wall was observed. Mean BSUV, standard deviation (SD), and standard error of the mean (SE) were computed for three groups of patients at each site, investigated 2 years apart, respectively, with group sizes between 53 and 100 patients. Differences of mean BSUV between the individual groups and sites were determined.ResultsSD (SE) of BSUV in the different groups ranged from 14.3 to 20.7% (1.7 to 2.8%). Differences of mean BSUV between intra-site groups were small (1.1–6.3%). Only one out of nine of these differences reached statistical significance. Inter-site differences were distinctly larger (12.6–25.1%) and highly significant (P<0.001).ConclusionsImage-based determination of the group-averaged blood SUV in modestly large groups of whole-body FDG-PET investigations is a viable approach for ensuring consistent scanner calibration over time and across different sites. We propose this approach as a quality control and cross-calibration tool augmenting established phantom-based procedures.
Highlights
The current de facto standard for quantification of tumor metabolism in oncological whole-body positron emission tomography (PET) is the standardized uptake value (SUV) approach
There is a slight decrease of measured blood SUV (BSUV) over time (P < 0.02) which is essentially removed after normalization
In view of the relatively small inter-subject variability (SD between 14.3 and 20.7%), the mean BSUV could be determined with high statistical accuracy in all patient groups for the chosen group sizes (SE between 1.7 and 2.8%)
Summary
The current de facto standard for quantification of tumor metabolism in oncological whole-body PET is the standardized uptake value (SUV) approach. Residual inaccuracies of the calibration lead to biased SUV values This can adversely affect multicenter trials where it is difficult to ensure reliable cross-calibration across participating sites. SUV computation requires quantitative determination of the tracer concentration with PET which in turn necessitates a regularly performed thorough scanner calibration (and crosscalibration against a dose calibrator) based on suitable phantom measurements adhering to standardized procedures [2, 4,5,6]. Residual inaccuracies of the calibration procedure or inadequacies that manifest themselves only in vivo lead to SUV values which might be systematically biased relative to the true values This can adversely affect multicenter trials [7]. Otherwise, existing systematic calibration differences between sites need to be corrected by suitable cross-calibration factors between the different centers/PET systems to enforce data consistency [10]
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