The understanding of radiation quality requires knowledge about the energy deposition pattern of ionizing radiation on which models for cellular and sub-cellular damage can be built. Experimental data is fundamental in this context for quality assurance and bench-marking of models and simulations. Direct measurements are also of practical importance for radiation quality determinations in radiation therapy and radiation protection.
In the experimental microdosimetric variance-covariance method, the radiation quality is determined from the dose average lineal energy (yD) that is used as an approximation of the dose average linear energy (LETD). The method has been successfully used in several radiation protection applications and the importance of the dose average lineal energy determined at 10 nm object sizes has also shown to be of potential importance for radiation quality measurements in radiation therapy.
There is however a need for detector and method development to obtain robust dose average lineal energy measurements with sufficiently low uncertainties at 10 nm or smaller object sizes.
The objectives of this project were to give an overview of existing microand nanodosimetric detectors and measurement techniques, identify a few potentially promising detector types and geometries for measurement of the dose-average lineal energy for 10 nm objects using the variance-covariance method, summarize simulation needs for the development of a suitable detector design, and to outline a suitable strategy for detector and method development for improvement of experimental nanodosimetry using the variance-covariance method.
Conventional ion chambers with low-noise electrometers has been used for nanodosimetry with the variance-covariance method down to the 10 – 50 nm range. It is concluded that this is also a potentially promising approach even for smaller object sizes. A better understanding of the influence from secondary electrons and anode, together with an improved electrometer design are though needed. Some additional development needs for detectors and simulations, as well as potential novel detector solutions for the variance-covariance method are briefly outlined.