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

METHODS

: Dual energy CT (DECT) images of 9 female mice were used to extract the effective atomic number Z and the relative electron density ρ 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/ρ were calculated for 10 different tissues in each mouse.

RESULTS

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/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.

CONCLUSION

: 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/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.

ADVANCES IN KNOWLEDGE

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