RT Journal Article SR Electronic T1 Optimizing Reconstruction Parameters Allows Dose Reduction in Pediatric Oncology Patients with Delayed Total-Body FDG PET/CT JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 241358 OP 241358 VO 65 IS supplement 2 A1 Mingels, Clemens A1 Spencer, Benjamin A1 NALBANT, HANDE A1 Rokni, Mehrad A1 Omidvari, Negar A1 Rominger, Axel A1 Sen, Fatma A1 Cherry, Simon A1 Badawi, Ramsey A1 Abdelhafez, Yasser A1 Nardo, Lorenzo YR 2024 UL http://jnm.snmjournals.org/content/65/supplement_2/241358.abstract AB 241358 Introduction: Given the increased signal collection efficiency, total-body (TB) PET/CT allows for protocol flexibility including dose reduction which is of particular interest in pediatric patients undergoing multiple PET/CT examinations. Therefore, the aim of the study was to define a lower limit of reduced injected dose in delayed [18F]FDG TB PET/CT without loss of diagnostic image quality in pediatric oncology patients.Methods: In this single-center study, 19 children (12 y/o (5-17y), 54.53±19.75kg) were scanned for 20 min with TB PET/CT, 120 min after administration of 4.07±0.49 MBq/kg [18F]FDG intravenously. Five low-count reconstructions without replacement were generated using 1/4th, 1/8th, 1/16th, 1/32nd of the counts of the randomly resampled full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. Follow-up [18F]FDG TB PET/CT from 12/19 patients were used to select the optimal reconstruction parameters for the simulated low-dose protocols. Low-count reconstruction protocols with varying number of iterations (4-6) and smoothing filters (46 mm FWHM Gaussian or non-local means (NLM)) were evaluated and compared to the full-dose dataset reconstructed with 4 iterations (20 subsets), 256x256 matrix, and with no smoothing, which is the clinical standard at our institution. All reconstructions were simultaneously displayed and independently rated from 1 (best) to 4 (worst) for interpretation/diagnosis by three nuclear medicine physicians.Optimal reconstruction parameters selected for each low-dose protocol were used with the initial staging scans of the 19 patients to define the lower limit of dose reduction for pediatrics. Background uptake was measured on the low-count reconstructions and compared to the clinical reference standard image, with volumes-of-interest (VOI) placed on the ascending aorta, right liver lobe, and lumbar vertebra body three (L3). Tumor lesions were segmented using a 40% iso-contour VOI approach. Coefficient-of-variation (COV), tumor-to-background ratio (TBR), and contrast-to-noise ratio (CNR) were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale.Results: In total, 113 malignant lesions were identified in the full-dose PET/CT in 18/19 patients, who met the inclusion criteria. 87.6% of the lesions were quantifiable. Lowest COV was detected in the 20 min reference standard. All low-count reconstructions obtained significantly higher COV (p<0.0001). Tumor uptake (SUVmax), TBR, and total lesion count were significantly lower in the reconstructions with 1/16th and 1/32nd counts of the reference standard (p<0.05). CNR and clinical image quality were significantly lower in all low-count reconstructions compared to the reference standard. Additionally, readers selected the reference reconstruction parameters for the 1/4th and 1/8th dose reduction (4 iterations, 20 subsets, no filter), but preferred additional smoothing by applying either Gaussian or NLM filters on 1/16th and 1/32nd respectively to compensate for the higher COV. Conclusions: Dose reduction with delayed [18F]FDG TB PET/CT imaging in children is possible without loss of subjective image quality or lesion conspicuity after optimizing TB PET/CT reconstruction parameters. However, our results indicate that PET centers should not reduce the dose below 0.5 MBq/kg (1/8th of 4.07MBq/kg) for [18F]FDG pediatric imaging at 120-min p.i. to maintain diagnostic image quality and provide conclusive images to the pediatric oncologists.