Abstract
2385
Introduction: To explore the effects of total-body PET/CT with half-dose 18F-FDG activity on image quality and lesion detectability in pediatric oncological patients, and investigate the ultra-low-dose of administered tracer activity.
Methods: A total of 100 pediatric oncological patients who underwent total-body PET/CT using a uEXPLORER scanner with half-dose (1.85 MBq/kg) 18F-FDG activity were prospectively enrolled from May 2021 to December 2021. All patients were confirmed by postoperative pathologic examination or biopsy.
The acquisition time of the half-dose group was 600s. The PET images were first constructed using all 600s data and were further split into 300s, 180s, 60s, 40s and 20s duration groups, which were all referred to as G600s to G20s respectively, by truncating the list-mode PET data to stimulate low-dose images (0.06-0.93 MBq/kg).
Image quality was evaluated by subjective and objective indicators. The subjective analysis method was assessed with 5-point Likert scales. Objective quantitative metrics of PET image quality included the SUVmax, SUVmean and and standard deviation (SD) of the liver, the spleen and blood pool. The variability in lesion SUVmean, SUVmax and tumour-to-background ratio (TBR) were also calculated. The full-time PET images served as the reference for other duration groups to evaluate lesion detectability.
Results: The mean and SD of the overall image quality scores in G600s, G300s, G180s and G60s were 4.9 ± 0.2, 4.9 ± 0.3, 4.4±0.5 and 3.5±0.5, respectively. Image quality scores in G20s (2.0 ± 0.5) were significantly lower than other groups (all p< 0.05). Sufficient subjective image quality and lesion conspicuity could be maintained down to G60s (1/20-dose, 0.185 MBq/kg) of the administered dose of 18 F-FDG. The image noise was more deranged than the overall quality and lesion conspicuity. 100% of the micro-lesions identified in half-dose images were localized down to G60s images; while 92% and 56% and of the lesion could be clearly identified in G40s (1/30-dose) and G20s (1/60-dose) images, respectively.
With stimulated reduced doses, SUVmax and SD of backgrounds were gradually increased, while TBR values showed no statistically significant deviation among groups (all p > 0.1). Half-dose images as reference, the bias and variability in lesion SUVmean and SUVmax in all age groups were not significant (all p > 0.1).
Conclusions: Total-body PET/CT with half-dose 18F-FDG achieved good performance in pediatric oncological patients ensuring sufficient image quality and lesion conspicuity. Optimal image quality could be achieved with an administered dose-reduction down to G60s (1/20-dose, 0.185 MBq/kg).