The Use of Monte-carlo Codes for Treatment Planning in External- Beam Radiotherapy

Monte Carlo simulation of radiation transport is a very powerful technique. There are basically no exact analytical solutions to the Boltzmann Transport equation. Even the "straightforward" situation (in radiotherapy) of an electron beam depth-dose distribution in water proves to be too difficult for analytical methods without making gross approximations such as ignoring energy-loss straggling, large-angle single scattering and bremsstrahlung production. Monte Carlo is essential when radiation is transported from one medium into another. As the particle (be it a neutron, photon, electron, proton) crosses the boundary then a new set of interaction cross-sections is simply read in and the simulation continues as though the new medium were infinite until the next boundary is encountered.