Analysis of image data from the EuroNet PHL-C2 trial indicates a potential reduction in injected F-18 FDG activities in children: a proposal to update the EANM Paediatric Dosage Card

Abstract

Background: The aim of this work is to provide the currently missing evidence that may allow an update of the Paediatric Dosage Card provided by the European Association of Nuclear Medicine (EANM) for conventional PET/CT systems.

Methods: In a total of 2082 consecutive [¹⁸F]FDG-PET scans performed within the EuroNet-PHL-C2 trial, the administered [¹⁸F]FDG activity was compared to the activity recommended by the EANM Paediatric Dosage Card. None of these scans had been rejected beforehand by the reference nuclear medicine panel of the trial because of poor image quality. For detailed quality assessment, a subset of 91 [¹⁸F]FDG-PET scans, all performed in different patients at staging, was selected according to pre-defined criteria, which (a) included only patients who had received substantially lower activities than those recommended by the EANM Paediatric Dosage Card, and (b) included as wide a range of different PET systems and imaging parameters as possible to ensure that the conclusions drawn in this work are as generally valid as possible. The image quality of the subset was evaluated visually by two independent readers using a quality scoring system as well as analytically based on a volume-of-interest analysis in 244 lesions and the healthy liver. Finally, recommendations for an update of the EANM Paediatric Dosage Card were derived based on the available data.

Results: The activity recommended by the EANM Paediatric Dosage Card was undercut by a median of 99.4 MBq in 1960 [¹⁸F]FDG-PET scans and exceeded by a median of 15.1 MBq in 119 scans. In the subset analysis (n = 91), all image data were visually classified as clinically useful. In addition, only a very weak correlation (r = 0.06) between activity reduction and tumour-to-background ratio was found. Due to the intended heterogeneity of the dataset, the noise could not be analysed statistically sound as the high range of different imaging variables resulted in very small subsets. Finally, a suggestion for an update of the EANM Paediatric Dosage Card was developed, based on the analysis presented, resulting in a mean activity reduction by 39%.

Conclusion: The results of this work allow for a conservative update of the EANM Paediatric Dosage Card for [¹⁸F]FDG-PET/CT scans performed with conventional PET/CT systems.

Keywords: Activity reduction; EANM Paediatric Dosage Card; EuroNet-PHL-C2 trial; New activity recommendation for [18F]FDG-PET; Radiation protection; [18F]FDG dosage; [18F]FDG-PET.

Fig. 1

Baseline characteristics of the subset of 91 selected [¹⁸F]FDG scans from the EuroNet-PHL-C2 trial. Histograms of weight (top left, bin size = 5 kg), age (bottom left, bin size = 1 year) and administered activity as well as activity recommended by the EANM Paediatric Dosage Card (right, bin size = 10 MBq). Vertical dashed lines indicate the mean activities. The cyan box marks the weight range > 68 kg not defined by the EANM Paediatric Dosage Card

Fig. 2

Examples of the visual assessment of image quality for still acceptable image quality (a QSV of 4.0) and very good image quality (b QSV of 7.5). A transversal slice (top left) and axial slices of the three areas considered in the assessment are shown: neck (top right), mediastinum (centre right) and liver (bottom right). The scores of the three areas considered as well as the total score are given at the bottom

Fig. 3

Linear regression analysis of the TBR in a 1-ml lesion (healthy liver background) based on the activity reduction $\mathrm{\Delta }A\%$ showing a very weak correlation (Pearson correlation coefficient, r(242) = 0.06, p = 0.352). The regression line (slope, 1.16 ± 1.35 MBq/kg and intercept, 5.21 ± 0.60 MBq) is plotted in green with 95% confidence intervals plotted in grey

Fig. 4

Activities recommended by the current EANM Paediatric Dosage Card (orange) [4] suggested update based on this work (green), and 3.7 MBq/kg activity regimen (blue line) as a function of body weight. In addition, the administered activities from all 2082 patient scans (grey dots) and the subset used in this study are given (dark red dots). Lastly, patients with body weight > 68 kg are indicated by the red box