Physikalisch-Technische Bundesanstalt

An update on developments in nanodosimetry and experimental track structure research and its applications

Kolloquium der Abteilung 6

Track structure of charged particle radiation with resolution of a few nanometers has been recognized as one of the most important determinants of the biological quality of ionizing radiation. For hadron therapy, better characterization of track structure with nanometer resolution may allow us to perform biologically weighted optimization and reduction of distal range uncertainties related to variations in relative biological effectiveness.

Track structure research comprises Monte Carlo simulation of the interaction of charged particles with subcellular structures and the development of detectors that investigate real charged particle tracks in gaseous or solid-state detectors. Over the last 15 years, we have invested in experimental track structure research related to the detection and counting of radiation induced ions with nanometer spatial resolution. Currently we are investigating a new and compact gaseous detector for precise imaging of the track structure of ionizing radiation (“track imaging detector”). The new instrument utilizes ion impact ionization in a hole-pattern array for single-ion 2D registration in low-pressure gas. In combination with drift time measurements this will provide the full 3D track structure reconstruction.

A biophysical model translating ion cluster size distributions obtained to cell survival RBE of standard cell lines has been developed and employed for a straightforward quality factor model that calculates the ratio of clustered double strand breaks induced by a mixed radiation field and a low-LET reference radiation based on cluster size measurements or simulations.

---