A realistic multiregion mouse kidney dosimetry model to support the preclinical evaluation of potential nephrotoxicity of radiopharmaceutical therapy

Suborgan absorbed dose estimates in mouse kidneys are crucial to support preclinical nephrotoxicity analyses of α- and β-particle-emitting radioligands exhibiting a heterogeneous activity distribution in the kidneys. This is, however, limited by the scarcity of reference dose factors (S values) available in the literature for specific mouse kidney tissues. Methods: A computational multiregion model of a mouse kidney based on high-resolution MRI data from a healthy mouse kidney was developed. The model was used to calculate S values for 5 kidney tissues (cortex, outer and inner stripes of outer medulla, inner medulla, and papilla and pelvis) for a wide range of β- or α-emitting radionuclides (45 in total) of interest for radiopharmaceutical therapy, using Monte Carlo calculations. Additionally, regional S values were applied for a 131I-labeled single-domain antibody fragment with predominant retention in the outer stripe of the renal outer medulla. Results: The heterogeneous activity distribution in kidneys of considered α- and low- to medium-energy β-emitters considerably affected the absorbed dose estimation in specific suborgan regions. The suborgan tissue doses resulting from the nonuniform distribution of the 131I-labeled antibody fragment largely deviated (from -40% to 57%) from the mean kidney dose resulting from an assumed uniform activity distribution throughout the whole kidney. The absorbed dose in the renal outer stripe was about 2.0 times higher than in the cortex and in the inner stripe and about 2.6 times higher than in inner tissues. Conclusion: The use of kidney regional S values allows a more realistic estimation of the absorbed dose in different renal tissues from therapeutic radioligands with a heterogeneous uptake in the kidneys. This constitutes an improvement from the simplistic (less accurate) renal dose estimates assuming a uniform distribution of activity throughout kidney tissues. Such improvement in dosimetry is expected to support preclinical studies essential for a better understanding of nephrotoxicity in humans. The dosimetric database has added value in the development of new molecular vectors for radiopharmaceutical therapy.