Mesh-type reference computational phantoms (MRCPs) for the next general recommendations

A full set of ICRP mesh-type reference computational phantoms (MRCPs), including adult, paediatric, and pregnant-female phantoms, is under development to produce dose coefficients for the next General Recommendations. The MRCPs are high-fidelity human models for radiation protection dosimetry, including all the source and target regions for effective dose calculations. The phantoms include micron-thick stem cell layers in the respiratory and alimentary tract organs, urinary bladder, and skin. The phantoms also include very detailed eye models and skeletal models. The MRCPs are developed in the fourth-generation phantom geometry, i.e. tetrahedron mesh geometry. This geometry, classified as an unstructured volume mesh, provides several key advantages. Firstly, it allows the phantoms to be directly incorporated into various Monte Carlo codes, such as Geant4, MCNP6, PHITS, and EGSnrc, without the need for voxelisation. This preserves the original high fidelity of the mesh phantoms during dose calculations, ensuring the most accurate results. The tetrahedron mesh geometry is volume representation, not surface or boundary representation, and provides the capability of suborgan/structure density variation modelling using the tetrahedra. A notable aspect of the mesh technology is its flexibility, allowing the phantoms to be easily adjusted for different body shapes and postures as required. In this article, the deformability of the MRCPs will be highlighted by reporting that the MRCPs were deformed into a library of 212 phantoms for adults and 637 phantoms for adolescents and children to represent different body sizes and shapes. It will also be reported that the phantoms were deformed into several different postures.