Monte Carlo simulation of the relative biological effectiveness and DNA damage from a 400 MeV/u carbon ion beam in water

A 400 MeV/u carbon ion beam incident on a water phantom was simulated with GATE/Geant4 to calculate the energy spectra of 12C and its fragments at various depths. Based on the energy spectra, the DNA double strand break (DSB) yields from 12C and its fragments were calculated with Monte Carlo Damage Simulation (MCDS) code. The relative biological effectiveness (RBE) distributions for 12C and its fragments were calculated from the DSB yields. The DNA damages from each type of the particles and their contribution to the total DNA damages at various depths were calculated from the DSB yields and dose distributions. These characteristics of 12C and its fragments are important for understanding the corresponding RBEs and the DNA damages. The purpose of this work was to obtain the RBEs and the DNA damage distributions of carbon ions and their fragments in beams used in radiotherapy by means of simulating the macroscopic phantom and microscopic cells. The simulation method can be easily extended by changing some parameters.