Nanodosimetry in a 12C ion beam using Monte Carlo simulations

The dose-mean lineal energy, y¯D, has been calculated in water for irradiation with 12C ions with initial energies 290 MeV/u. The y¯D was evaluated from the energy distributions of carbon and secondary boron ions, and from their energy-dependent y¯D-values. The energy distributions were obtained from simulations with the Monte Carlo code SHIELD-HIT07 and the energy-dependent y¯D-values were obtained from ion-track simulations with PITS99 coupled with the electron transport code KURBUC. The ratio of the y¯D-value determined in the vicinity of the Bragg peak to that calculated in a reference 60Co γ beam was compared with the corresponding ratio of α-values from the linear-quadratic model used in fractionated radiotherapy, showing a good correlation for an object size of around 10 nm.