Verification of biological dose calculation for carbon ion therapy with a Monte Carlo method

We developed a calculation technique to evaluate the biological dose distribution of heavy ion beams, and verified its reliability by comparison with experimental results. The calculation technique was developed by connecting two general-purpose Monte Carlo codes. In order to evaluate the radiation quality and biological effect, the microdosimetric kinetic model was adopted. We estimated the distribution of physical dose and radiation quality for the carbon broad beam with experiments and with Monte Carlo calculations. Relative biological effectiveness (RBE) was estimated from radiation quality, and biological dose could be calculated as the product of the physical dose and the RBE. Our calculations showed good agreement with experiments, not only for the physical dose, but also for the dose-averaged lineal energy as an expression of radiation quality and therefore biological dose. This finding indicates that our calculation tool will be useful to estimate biological dose distribution in the design of heavy ion radiation facilities or for quality assurance in treatment planning. (author)