Considerations of coherent scattering and electron binding in incoherent scattering, in computation of dose deposition in tissue from low-energy photon beams

Two different sets of Monte Carlo computations were carried out for the study of dose penetration of monoenergetic, low-energy (10 to 100 keV) photon beams incident on slabs of tissue. One program took into account coherent scattering and considered electron binding when finding the angle of scattering during incoherent scattering; the other simpler program, customarily used at higher energies, largely ignored these effects. For calculations at the source photon energy of 100 keV, it was found that there was negligible difference in dose distribution in the slab between the more and less complex type of calculations. The same thing was found to be true for the 30 and 10-keV source photon energies only for shallow penetration distances; and at deeper penetrations the simple approach tended to overestimate the dose appreciably. It is concluded that for penetration of low-energy photon beams into tissue, accurate calculational results cannot be assured with the neglect of coherent scattering effects and electron binding considerations in determining the scattering angles except for shallow depths of penetration.