Pediatric tumor patients scanned with a long axial field of view scanner – a single center experience on the use of lower administered doses of [18F]FDG

Introduction: The administered activity for [18F]FDG-PET/CT in pediatric patients has been a topic of ongoing discussion. Current guidelines suggest a dose range of 3.7-5.2 MBq/kg body weight (BW). With the technological advancements in the latest generation scanners, there is a promising opportunity to reduce the administered dose. In this evaluation, we present our experiences with pediatric tumor patients who underwent PET/CT scans using reduced doses on a long axial field of view (LAFOV) scanner.

Methods: 25 [¹⁸F]FDG-PET/CT conducted with LAFOV-PET/CT scanner (field-of-view: 106 cm) in 18 children and adolescences (age < 18 y/o) were included in this retrospective analysis. Amongst them, three groups were identified depending on the administered activity: 1 MBq per kg body weight, 2 MBq/kg BW and 3 MBq/kg BW. Acquisition duration was 10 minutes for all groups starting 1h post injection. In addition to the before-mentioned three groups, a fourth group was created by simulating 0.5 MBq/kg BW by artificially reconstructing all images conducted with the before-mentioned activities. In addition, 12 scans conducted with a high-end standard axial FOV scanner (field-of-view: 26.3 cm) in nine children were comparatively assessed. The quality of all scans was assessed in a blinded manner by four readers using a 5-point Likert scale, where a score of 5 indicated the best quality and a score of 1 indicated the worst. The differences were evaluated using the Kruskal-Wallis test, and a p-value lower than 0.05 was deemed to be statistically significant.

Results: The mean (± SD) Likert scale of the different groups were as follows: 2.7 ± 0.66 for 0.5 MBq/kg; 3.4 ± 0.75 for 1 MBq/kg; 4.4 ± 0.53 for 2 MBq/kg, 5.0 ± 0 for 3 MBq/kg and 2.88 ± 0.79 for the group acquired on a standard FOV scanner. There was a significant association between higher activities and higher Likert scales: p=0.004 for the comparison between group 1 MBq/kg vs. group 0.5 MBq/kg, p=0.002 for the comparison between group 2 MBq/kg vs. group 1 MBq/kg and p=0.013 for the comparison between group 3 MBq/kg vs. group 2 MBq/kg. No significant difference was found between the 1 MBq/kg group and the group scanned with the high-end standard FOV scanner (p = 0.23). On the other hand, the image quality of the 0.5 MBq/kg group was lower compared to the standard FOV group (p=0.013).

Conclusions: The image quality achieved using a dose of 3 MBq/kg with the LAFOV-PET/CT scanner was exceptional, despite being lower than the recommended dose stated in the guidelines, which were established based on data from standard FOV scanners. As anticipated, image quality noticeably declined when lower doses of [18F]FDG were used. However, scans performed with a dose of 1 MBq/kg on the LAFOV-PET/CT scanner yielded comparable quality to scans conducted with a full dose on a standard FOV scanner. Depending on the specific clinical requirement, the dose can be further adjusted to meet the clinical needs.