Author: Wesley E. Bolch, Chansoo Choi, Chan Hyeong Kim, Suhyeon Kim, Bangho Shin, Yeon Soo Yeom 👨🔬
Affiliation: Hanyang University, University of Florida, 2) Department of Radiation Convergence Engineering, Yonsei University 🌍
Purpose: Task Group 103 of International Commission on Radiological Protection (ICRP) recently released new-generation adult and pediatric mesh-type reference computational phantoms (MRCPs) via ICRP Publications 145 and 156. In the present study, we developed the final series of MRCP—the pregnant-female MRCPs—representing pregnant women with the male or female fetus at fetal ages (=conceptual ages) of 8, 10, 15, 20, 25, 30, 35, and 38 weeks.
Methods: Prior to phantom construction, datasets specific to fetal age—including organ data (i.e., masses, densities, and elemental compositions) and anthropometric measurements (e.g., maternal breast morphology and fetal crown-rump length)—were established. The pregnant-female MRCPs were then constructed in high-fidelity mesh format using the adult female and newborn MRCPs, abdominal organs of University of Florida (UF) pregnant female phantom series, and UF and Ferdowsi University of Mashhad fetal phantom series. To investigate dosimetric impact of the developed phantoms, specific absorbed fractions (SAFs) were calculated for selected maternal organs as source regions and the entire fetus as a target region using Geant4 Monte Carlo code.
Results: The present study developed a set of pregnant-female MRCPs, including both maternal and fetal phantoms, in a tetrahedral volume mesh format. This format features the advantages of both voxel and boundary representation (BREP) formats, such as sub-organ density variation and fast computation speed. In terms of dose estimates, the pregnant-female MRCPs exhibited age-dependent SAF trends, with values varying predicably with fetal age based on source-target distance.
Conclusion: The pregnant-female MRCPs faithfully reflect maternal and fetal anatomy of different fetal ages, providing reliable dose values. As the first ICRP reference phantoms for pregnant women and fetuses, these phantoms will be used for the calculation of reference dose coefficients following both the current ICRP 2007 recommendations and the forthcoming general recommendations. They will also have broad applications, including medical exposures such as nuclear medicine.