Murine vs human tissue compositions: implications of using human tissue compositions for photon energy absorption in...

Dual energy CT (DECT) images of 9 female mice were used to extract the effective atomic number Z_eff and the relative electron density ρ_e for each voxel in the images. To investigate the influence of the tissue compositions on the absorbed radiation dose for a typical kilovoltage photon beam, mass energy-absorption coefficients μ_en/ρ were calculated for 10 different tissues in each mouse.

Differences between human and murine tissue compositions can lead to errors around 7.5 % for soft tissues and 20.1 % for bone tissues in μ_en/ρ values for kilovoltage photon beams. When considering the spread within tissues, these errors can increase up to 17.5 % for soft tissues and 53.9 % for bone tissues within only a single standard deviation away from the mean tissue value.

This study illustrates the need for murine reference tissue data. However, assigning only a single mean reference value to an entire tissue can still lead to large errors in dose calculations given the large spread within tissues of μ_en/ρ values found in this study. Therefore, new methods such as DECT and spectral CT imaging need to be explored, which can be important next steps in improving tissue assignment for dose calculations in small animal radiotherapy.

This is the first study that investigates the implications of using human tissue compositions for dose calculations in mice for kilovoltage photon beams.