Development of paediatric mesh-type reference computational phantom series of International Commission on Radiological Protection

Abstract

Very recently, Task Group 103 of the International Commission on Radiological Protection (ICRP) completed the development of the paediatric mesh-type reference computational phantoms (MRCPs) comprising ten phantoms (newborn, one year-old, five year-old, ten year-old, and fifteen year-old males and females). The paediatric MRCPs address the limitations of ICRP Publication 143’s paediatric reference computational phantoms, which are in voxel format, stemming from the nature of the voxel geometry and the limited voxel resolutions. The paediatric MRCPs were constructed by converting the voxel-type reference phantoms to a high-quality mesh format with substantial enhancements in the detailed anatomy of the small and complex organs and tissues (e.g. bones, lymphatic nodes, and extra-thoracic region). Besides, the paediatric MRCPs were developed in consideration of the intra-organ blood contents and by modelling the micron-thick target and source regions of the skin, lens, urinary bladder, alimentary tract organs, and respiratory tract organs prescribed by the ICRP. For external idealised exposures, the paediatric MRCPs provide very similar effective dose coefficients (DCEs) to those from the ICRP-143 phantoms but significantly different values for weakly penetrating radiations (e.g. the difference of ∼20 000 times for 10 keV electron beams). This paper introduces the developed paediatric MRCPs with a brief explanation of the construction process. Then, it discusses their computational performance in Geant4, PHITS, and MCNP6 in terms of memory usage and computation speed and their impact on dose calculations by comparing their calculated values of DCEs for external exposures with those of the voxel-type reference phantoms.

Development of Respiratory Tract Organs for ICRP Pediatric Mesh-type Reference Computational Phantoms

“…The respiratory tract organs of the pediatric MRCPs were produced first by converting the University of Florida and National Cancer Institute (UF and NCI) pediatric phantoms (Lee et al 2010) into the polygonal mesh (PM) format and then by matching the mesh models to the pediatric VRCPs (ICRP 2020a), following the procedure shown in Fig. 2, which also had been used in previous studies (Choi et al 2021a and b, 2022; Yeom et al 2022). Note that the UF and NCI phantoms in the non-uniform rational B-spline (NURBS) and PM formats are the origins of the pediatric VRCPs (i.e., before voxelization and other adjustment processes), which strongly facilitated their conversion to the high-quality PM format.…”

“…Next, the μm-thick target and source regions prescribed in ICRP 66 (Tables 1 and 2) were defined in the respiratory tract of the pediatric MRCPs. For the ET 1 , ET 2 , tracheal, and main BB regions, the target and source regions were defined simply by uniformly enlarging the airway surface following the method applied in previous studies (ICRP 2020b; Kim et al 2017; Choi et al 2021a, 2022). However, this method could not be applied to the other airway generations of the BB region (airway generations 2–8) or to any of the subsequent generations of the bb region (airway generations 9–15) because they are not represented in the pediatric VRCPs and, consequently, in the pediatric MRCPs.…”

“…The adult MRCPs include the complex and small organs, even all of the μm-thick target and source regions prescribed by the ICRP (ICRP 1994, 2006, 2010), thereby significantly improving the dosimetric accuracy relative to the adult VRCPs (Nguyen et al 2015; Yeom et al 2016a–c, 2019, 2020; Kim et al 2017; ICRP 2020a). Following the completion of the adult MRCPs, TG 103 recently completed the development of the pediatric (newborn, 1-, 5-, 10-, and 15-y-old) male and female MRCPs (Choi et al 2021a and b, 2022; Shin et al 2021; Han et al 2021; Yeom et al 2022) and the mesh counterparts of the pediatric VRCPs of ICRP Publication 143 (ICRP 2020a), which share functionally the same level with that of the adult MRCPs.…”

“…Following up on our previous studies (Choi et al 2021a andShin et al 2021;Han et al 2021;Yeom et al 2022), in the present study, we developed a new set of respiratory tract organs for the pediatric MRCPs, consisting of the following regions: extrathoracic (ET 1 and ET 2 ), bronchial (BB, airway generations 0-8), bronchiolar (bb, airway generations 9-15), and alveolar-interstitial (AI) regions. The ET 1 , ET 2 , tracheal (airway generation 0), and main BB (airway generation 1) regions and exterior lung boundaries were developed by converting those of the pediatric VRCPs into the mesh format with anatomical improvement, especially in the ET 2 region.…”

A Review of Computational Phantoms for Quality Assurance in Radiology and Radiotherapy in the Deep-Learning Era

“…These phantoms are the next generation of ICRP pediatric (newborn, 1-, 5-, 10-, and 15-yearold male and female) reference phantoms in a mesh format that will replace those of ICRP Publication 143 in a voxel format. Choi et al [153] introduced developed pediatric MRCPs with a brief explanation of the development process and discussed their computational performance in the general-purpose Monte Carlo codes.…”