Developments in microdosimetry and nanodosimetry for space and therapeutic applications

Author

Andrew J. Wroe, University of Wollongong

Year

2007

Degree Name

Doctor of Philosophy

Department

Department of Engineering Physics - Faculty of Engineering

Recommended Citation

Wroe, Andrew J, Developments in microdosimetry and nanodosimetry for space and therapeutic applications, PhD thesis, Department of Engineering Physics, University of Wollongong, 2007. http://ro.uow.edu.au/theses/58

Abstract

This thesis further applies solid-state microdosimetry and low-pressure gas nanodosimetry to both radiation therapy and radiation protection. A number of unique applications have been identified where considerable advancements could be made with current technology and consequently have a significant bearing on developments in these fields.

Silicon-on-Insulator (SOl) microdosimetry technology was utilised to provide a complete and detailed analysis of out-of-field dose equivalents for proton therapy. The superior device spatial resolution and established quality factors of the microdosimetry method allowed for a new perspective on this issue. Microdosimetric measurements within heterogeneous tissue equivalent phantoms were also completed to discern measurable changes in radiation field as a function of preceding phantom material and if such changes should be included in treatment planning calculations. These measurements were correlated with Monte Carlo simulations for experimental validation and further analysis oftreatment planning parameters.

The application of SOl microdosimetry to space radiation was also tested with an experimental and theoretical analysis. Experimentally the devices were tested within homogeneous Perspex phantoms irradiated with a range of heavy ions including iron, titanium and oxygen. The microdosimetric parameters of these fields and the ability of the SOl microdosimeter to be applied in such fields was evaluated and established. This was further supported through theoretical simulations of the SOl icrodosimeters response to solar protons prior to their deployment aboard the MidSTAR-I satellite. It is expected that such devices will make a valuable contribution evaluating the complex radiation field in space while at the same time establishing improvements for the next generation of devices.

A new monolithic silicon AE-E telescope was evaluated in hadron therapy applications, obtaining data for both modulated and un-modulated therapeutic proton beams. This detector system provides two-dimensional information on LET and particle identification that is based on energy depositions, collected in coincidence, within the AE and E stages of the detector. This apparatus is advantageous over existing systems, that provide one-dimensional information on the lineal energy or LET spectra, as it allows for particles of differing type yet the same LET to be identified separately and the corresponding difference in both energy deposition properties and biological effect accounted for. To achieve this, a correlation matrix based on established in-vitro biology data was developed and verified to link the output of such a device directly to in-vitro radiobiological effect. This system has great application to both hadron therapy and radiation protection as it may provide a means for accurate real time analysis of the radiobiological properties of a complex mixed radiation field. It could be expected that such a system may form the basis of radiobiological treatment planning in hadron therapy.

Nanodosimetry is the next logical extension from microdosimetry, providing information on radiation track structure at a DNA or nanometre level which is dependant on particle type and energy. Experimental results were obtained for a range of proton energies and the results compared with Monte Carlo simulation codes in an effort to both validate these codes and evaluate the performance ofthe low-pressure gas nanodosimeter. The initial development of a biophysical model in nanodosimetry was also presented, which will be further developed in future work. A requirement for such development is accurate biological data for low energy ion radiations. To this end cell survival work was completed on a human glioma cell line for a range of proton energies and Co-60 control with the development of a thin-film cell survival protocol. It is expected that the expansion of this radiobiology protocol will allow for the further correlation of cell survival with AE-E telescope and nanodosimetry output. Such correlation and biophysical model development is useful in hadron therapy treatment planning and radiation protection applications as it directly links a measured physical quantity to biological effect through models that are based on accurate experimental data.