Ion-counting nano-dosemeter with particle tracking capabilities

An ion-counting nano-dosemeter (ND) yielding the distribution of radiation-induced ions in a low-pressure gas within a millimetric, wall-less sensitive volume (SV) was equipped with a silicon microstrip telescope that tracks the primary particles, allowing correlation of nano-dosimetric data with particle position relative to the SV. The performance of this tracking ND was tested with a broad 250 MeV proton beam at Loma Linda Univ. Medical Center. The high-resolution tracking capability made it possible to map the ion registration efficiency distribution within the SV, for which only calculated data were available before. It was shown that tracking information combined with nano-dosimetric data can map the ionisation pattern of track segments within 150 nm-equivalent long SVs with a longitudinal resolution of ∼5 tissue-equivalent nano-meters. Data acquired in this work were compared with results of Monte Carlo track structure simulations. The good agreement between 'tracking nano-dosimetry' data acquired with the new system and simulated data supports the application of ion-counting nano-dosimetry in experimental track-structure studies. (authors)