The absorbed dose for proton beam in water was calculated using the PTRAN code system. The proton interactions with water and the description on absorbed dose calculations are discussed, and the file structure and an execution example of the PTRAN codes are described. For 60, 100, 150, 200, and 250 MeV proton beams it is demonstrated that the absorbed dose is determined from the sum of Coulomb interactions and nuclear reactions, and that the Bragg peak feature depends on the energy straggling and multiple scattering. The PTRAN code was useful for studying the fundamental mechanism of the absorbed dose to water for clinical proton beams.

KeywordsProton beam, Absorbed dose, PTRAN code