Experimental nanodosimetry: Track structure of 80 MeV boron ions

Abstract

The radiobiological effects of ionising radiations are strongly correlated to the local density of lesions produced in micrometre- and nanometre-sized subcellular structures, and thus to the track structure properties of interacting particles. These properties have been studied mainly by means of Monte Carlo simulations, however experimental methodologies and instruments have also been developed that allow to measure the stochastics of ionisations produced in a nanometric sensitive volume (SV) by charged particles crossing it or passing nearby at specified distances. The number ν of ionisations produced in SV by the passage of a single primary ionising particle is measured, and the measurement is repeated many times to produce a probability distribution P(ν), called ionisation cluster size distribution. Measurable quantities can be derived that correlate with the biological effectiveness of the specific radiation quality (ion type and velocity). In view of the emerging interest of carbon ions in radiotherapy, it is important to characterize not only the track structure of carbon ions but also that of other light ions that are produced in nuclear interactions. This work presents first experimental results for boron ions at 80 MeV. Ionisation cluster size distributions were measured with the Startrack-Counter installed at the TANDEM-ALPI accelerator complex at the Legnaro National Laboratories (LNL) of the Italian Istituto Nazionale di Fisica Nucleare (INFN) and simulated by means of a dedicated Monte Carlo code. Measurements and simulations were performed for particles that traverse directly the sensitive volume or pass nearby at specified impact parameters.