Re-evaluation of pediatric ¹⁸F-FDG dosimetry: Cristy–Eckerman versus UF/NCI hybrid computational phantoms

Abstract

Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost all reported pediatric absorbed dose estimates, however, have been determined using adult pharmacokinetic data with radionuclide S values that take into account the anatomical differences between adults and children based upon the older Cristy-Eckerman (C-E) stylized phantoms. In this work, we use pediatric model-derived pharmacokinetics to compare absorbed dose and effective dose estimates for F-FDG in pediatric patients using S values generated from two different geometries of computational phantoms. Time-integrated activity coefficients ofF-FDG in brain, lungs, heart wall, kidneys and liver, retrospectively, calculated from 35 pediatric patients at the Boston's Children Hospital were used. The absorbed dose calculation was performed in accordance with the Medical Internal Radiation Dose method using S values generated from the University of Florida/National Cancer Institute (UF/NCI) hybrid phantoms, as well as those from C-E stylized computational phantoms. The effective dose was computed using tissue-weighting factors from ICRP Publication 60 and ICRP Publication 103 for the C-E and UF/NCI, respectively. Substantial differences in the absorbed dose estimates between UF/NCI hybrid pediatric phantoms and the C-E stylized phantoms were found for the lungs, ovaries, red bone marrow and urinary bladder wall. Large discrepancies in the calculated dose values were observed in the bone marrow; ranging between -26% to +199%. The effective doses computed by the UF/NCI hybrid phantom S values were slightly different than those seen using the C-E stylized phantoms with percent differences of -0.7%, 2.9% and 2.5% for a newborn, 1 year old and 5 year old, respectively. Differences in anatomical modeling features among computational phantoms used to perform Monte Carlo-based photon and electron transport simulations for F, and very likely for other radionuclides, impact internal organ dosimetry computations for pediatric nuclear medicine studies.

Patient-adapted organ absorbed dose and effective dose estimates in pediatric 18F-FDG positron emission tomography/computed tomography studies

“…Dose coefficients for urinary bladder, kidneys, heart, red bone marrow and lungs were estimated by OLINDA 2.0 to be lower than <1Y = patients aged less than one year at scan time 1-5Y = patients aged one year to five years old at scan time 6-10Y = patients aged five years to ten years old at scan time 11-15Y = patients aged eleven to fifteen years old at scan time 16-17Y = patients aged sixteen to seventeen years old at scan time SD = Standard Deviation <1Y = patients aged less than one year at scan time 1-5Y = patients aged one year to five years old at scan time 6-10Y = patients aged five years to ten years old at scan time 11-15Y = patients aged eleven to fifteen years old at scan time 16-17Y = patients aged sixteen to seventeen years old at scan time ICRP 128. Relative differences between ICRP 128 coefficients and those reported in our study are consistent with those demonstrated by Khamwan et al, in which lower lung and urinary bladder dose coefficients were attributed to improved approximation of adjacent organ boundaries as modeled by newer phantoms, compared to older stylized phantoms [32]. As a result of the organ dose differences between the two methods, the ED coefficients also differ, with those estimated by OLINDA 2.0 being approximately 34% less than those provided by ICRP 128.…”

Nuclear Medicine Dosimetry in Paediatric Population

“…Paediatric pharmacokinetic data are collected for diagnostic imaging agents, relevant to paediatric studies and the field conversions from older stylized phantoms to more detailed computation hybrid phantoms were created. The effective doses, computed by the UF/NCI hybrid phantom S values, were different than those seen using the C−E stylized phantoms for newborns, 1-year-old and 5 years old, Figures 3 and 4 [6].…”

“…RADAR Dose Estimates Report in 2018 based on OLINDA/EXM Version 2.0 for Radiopharmaceutical Dose Estimates [9]. [6].…”

“…Figure 4.Three-D visualization of University of Florida/National Cancer Institute (UF/NCI) hybrid computational phantoms for various age groups[6].…”

Investigating Low-Dose Image Quality in Whole-Body Pediatric 18F-FDG Scans Using Time-of-Flight PET/MRI

“…Investigation into the optimal radiotracer activity is critical to pediatric nuclear medicine because children have a higher sensitivity to develop radiation-induced malignancies (1)(2)(3)(4) . A major challenge to radiotracer dosing in pediatrics is the large variation in patient sizespanning an age range from newborn to >18 yrs-old-which impacts dosimetry calculations and image quality measurement techniques (5)(6)(7)(8)(9)(10) . There have been several studies evaluating how the radiotracer dose regimen affects pediatric image quality, and specifically for 18F-Fluorodeoxyglucose (18F-FDG), optimized regimens of 2.0 MBq/kg -5.3 MBq/kg (3 min/bed position) have been reported (11)(12)(13).…”