Mesh-based detailed human kidney models of the ICRP reference adults for radiopharmaceutical therapy dosimetry: macroscale models

Abstract Objective. In radiopharmaceutical therapy, the kidney is a major dose-limiting organ for many radiopharmaceuticals. The ICRP adult mesh-type reference computational phantoms (MRCPs) define the kidneys only with cortex, medulla, and pelvis regions, limiting the ability to characterize heterogeneous dose distributions within the kidneys. The present study aims to develop anatomically detailed macroscale kidney models for the adult MRCPs—comprising the capsule, cortex, medullary pyramids, papillae, pelvis wall, pelvis epithelium, and urine. Approach. The cortex, medullary pyramids, and papillae were constructed by segmenting 15 cadaveric kidney specimens and scaling them in accordance with the reference volumes and location, whereas the capsule, pelvis wall, pelvis epithelium, and urine were constructed based on target thicknesses. The developed models were integrated into the MRCPs and implemented in PHITS Monte Carlo code to compute absorbed fractions and specific absorbed fractions (SAFs) for photons, electrons, and alpha particles. The S values for clinically relevant therapeutic and diagnostic radionuclides were then derived using the SAF dataset and the ICRP Publication 107 decay data. Main Results. Anatomically detailed macroscale kidney models were developed for the adult male and female in a tetrahedral mesh format. The total masses were matched to the ICRP reference masses within 0.1% deviation. Compared with the original MRCP kidneys, the new kidney models produced substantial differences in SAFs, particularly for source–target combinations involving the renal pelvis, reflecting the more anatomically detailed representation of the collecting system. These differences resulted in corresponding differences in S values, depending on the radionuclide and source–target combination. Significance. The developed kidney model and established dataset enable subregional dose assessment within the kidney for radiopharmaceutical therapy dosimetry. This capability facilitates evaluation of heterogeneous dose distributions among kidney substructures and may support optimization of administered activity in treatment planning.