Water and tissue equivalence properties of biological materials for photons, electrons, protons and alpha particles in the energy region 10 keV-1 GeV: a comparative study.

Purpose: To compare some biological materials in respect to the water and tissue equivalence properties for photon, electron, proton and alpha particle interactions as means of the effective atomic number (Zeff) and electron density (Ne).

Methods: A Z-wise interpolation procedure has been adopted for calculation of Zeff using the mass attenuation coefficients for photons and the mass stopping powers for charged particles.

Results: At relatively low energies (100 keV-3 MeV), Zeff and Ne for photons and electrons were found to be constant while they vary much more for protons and alpha particles. In contrast, Zeff and Ne for protons and alpha particles were found to be constant after 3 MeV whereas for photons and electrons they were found to increase with the increasing energy. Also, muscle eq. liquid (with sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) within low relative differences below 9%. Muscle eq. liquid (without sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) with difference below 10%.

Conclusions: The reported data should be useful in determining best water as well as tissue equivalent materials for photon, electron, proton and alpha particle interactions.