Effects induced by the fine structure of biological tissues on microbeam dose deposition: A numerical study

In this work small angle coherent scattering data are presented for some biological tissues. The effect of low angle diffusion on the micro-beams dose distributions are assessed by means of a dedicated version of the EGS4 code. The atomic form factor tabulations were upgraded in EGS4 to include experimental values of compounds instead of obtaining the linear differential scattering coefficient from a simple weighted sum of the elemental components. In this manner, one includes the effects induced by both the large-scale arrangement of the sample structure and the molecular interference. It is shown that the inclusion of the measured form factors and cross-sections in the photon transport calculations induce not negligible effects in the dose deposited around the microbeams. The fact of not taking into account small angle scattering cross-sections may lead to underestimating the number of scattered photons reaching zones not directly illuminated. At the center of a microbeam planar array the effect can be as much as 100% for X-ray photons of 50 keV.