Track Structure of Light Ions: The Link to Radiobiology

It is generally recognized that the biological response to irradiation by light ions is initiated by complex damages at the DNA level. In turn, the occurrence of complex DNA damages is related to spatial and temporal distribution of ionization and excitation events, i.e., the particle track structure. It is the aim of the present study to investigate the correlation between the distribution of ionizations at the nanometric scale and the probability to induce biological damage. By means of Monte Carlo track structure simulations, the mean ionization yield [Formula: see text] and the cumulative probabilities [Formula: see text] , [Formula: see text] , and [Formula: see text] of at least one, two and three ionizations, respectively, were calculated in spherical volumes of water-equivalent diameters equal to 1, 2, 5 and 10 nm. When plotted as a function of [Formula: see text] , the quantities [Formula: see text] , [Formula: see text] and [Formula: see text] are distributed along almost unique curves, largely independent of particle type and velocity. However, the shape of the curves depends on the size of the sensitive volume. When the site size is 1 nm, biological cross sections are strongly correlated to combined probabilities of [Formula: see text] and [Formula: see text] calculated in the spherical volume, and the proportionality factor is the saturation value of biological cross sections.