Monte carlo simulation study on the dose and dose-averaged linear energy transfer distributions in carbon ion...

Dose-averaged linear energy transfer (LET_d) is conventionally evaluated from the relative biological effectiveness (RBE)-LET_d fitted function used in the treatment planning system. In this study, we calculated the physical doses and their linear energy transfer (LET) distributions for patterns of typical CIRT beams using Monte Carlo (MC) simulation. The LET_d was then deduced from the MC simulation and compared with that obtained from the conventional method. The two types of LET_d agreed well with each other, except around the distal end of the spread-out Bragg peak. Furthermore, an MC simulation was conducted with the material composition of water and realistic materials. The profiles of physical dose and LET_d were in good agreement for both techniques. These results indicate that the previous studies to analyze the minimum LET_d in CIRT cases are valid for practical situations, and the material composition conversion to water little affects the dose distribution in the irradiation field.