Investigation of the characteristics of carbon beam scanning irradiation implementing Monte Carlo simulations

The lateral beam spread of carbon due to the multiple scattering is smaller than that of proton beam. However, in the carbon beam therapy, the primary carbon beam collides with nuclei in the medium and a nuclear fragmentation occurs. Past experiment results show that the lateral spread is caused by not only the multiple scattering of the primary beam but also by the fragment particles scattering with a large angle in the transverse direction to the beam axis. The irradiation field is obtained by superposing sequentially deposited spot beams with a scanning technique but to estimate the effective beam spread, fragmentation information outside of the primary beam spread is also required. In this presentation, we describe the characteristics of fragment particles scattered in the large angles using the GEANT4 Monte Carlo simulation. (author)