Physical and biological characteristics of protons as well as technical requirements on proton beams are reviewed in order to illustrate the need for accurate proton transport simulations for therapeutic applications. Certain Monte Carlo proton transport simulation codes that have been used at therapeutic energies are briefly discussed. A general insight into two proton transport simulation schemes is presented; one including the generation and transport of secondary protons and the other comprising the generation and transport of secondary electrons. Based on different experiences gained, an analysis of the role of secondary particle is given
