Dose Reduction in Pediatric Oncology Patients with Delayed Total-Body [¹⁸F]FDG PET/CT

Abstract

Our aim was to define a lower limit of reduced injected activity in delayed [¹⁸F]FDG total-body (TB) PET/CT in pediatric oncology patients. <b>Methods:</b> In this single-center prospective study, children were scanned for 20 min with TB PET/CT, 120 min after intravenous administration of a 4.07 ± 0.49 MBq/kg dose of [¹⁸F]FDG. Five randomly subsampled low-count reconstructions were generated using ¼, ⅛, <math xmlns="http://www.w3.org/1998/Math/MathML" id="Mi1" display="inline" overflow="scroll"><mrow><mstyle scriptlevel="+1"><mfrac bevelled="true"><mn>1</mn><mrow><mn>16</mn></mrow></mfrac></mstyle></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" id="Mi2" display="inline" overflow="scroll"><mrow><mstyle scriptlevel="+1"><mfrac bevelled="true"><mn>1</mn><mrow><mn>32</mn></mrow></mfrac></mstyle></mrow></math> of the counts in the full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. For the 2 lowest-count reconstructions, smoothing was applied. Background uptake was measured with volumes of interest placed on the ascending aorta, right liver lobe, and third lumbar vertebra body (L3). Tumor lesions were segmented using a 40% isocontour volume-of-interest approach. Signal-to-noise ratio, tumor-to-background ratio, and contrast-to-noise ratio were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale. <b>Results:</b> In total, 113 malignant lesions were identified in 18 patients, who met the inclusion criteria. Of these lesions, 87.6% were quantifiable. Liver SUV_mean did not change significantly, whereas a lower signal-to-noise ratio was observed in all low-count reconstructions compared with the reference standard (<i>P</i> &lt; 0.0001) because of higher noise rates. Tumor uptake (SUV_max), tumor-to-background ratio, and total lesion count were significantly lower in the reconstructions with <math xmlns="http://www.w3.org/1998/Math/MathML" id="Mi3" display="inline" overflow="scroll"><mrow><mstyle scriptlevel="+1"><mfrac bevelled="true"><mn>1</mn><mrow><mn>16</mn></mrow></mfrac></mstyle></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" id="Mi4" display="inline" overflow="scroll"><mrow><mstyle scriptlevel="+1"><mfrac bevelled="true"><mn>1</mn><mrow><mn>32</mn></mrow></mfrac></mstyle></mrow></math> of the counts of the reference standard (<i>P</i> &lt; 0.001). Contrast-to-noise ratio and clinical image quality were significantly lower in all low-count reconstructions than with the reference standard. <b>Conclusion:</b> Dose reduction for delayed [¹⁸F]FDG TB PET/CT imaging in children is possible without loss of image quality or lesion conspicuity. However, our results indicate that to maintain comparable tumor uptake and lesion conspicuity, PET centers should not reduce the injected [¹⁸F]FDG activity below 0.5 MBq/kg when using TB PET/CT in pediatric imaging at 120 min after injection.

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