Doctor of Philosophy
School of Engineering Physics
Lian, Cheryl Pei Ling, Characterisation and application of the MOSkin radiation dosimeter at clinical kilovoltage x-ray energies, Doctor of Philosophy thesis, School of Engineering Physics, University of Wollongong, 2013. http://ro.uow.edu.au/theses/3935
X-ray Computed Tomography (CT) is an invaluable diagnostic imaging tool in clinical practice. However in recent years due to the widespread availability and burgeoning use of Multi-Slice CT (MSCT) scanners, cumulative lifetime radiation dose has increasingly become an issue of public concern. Currently, no real-time radiation dosimeter exists in the diagnostic radiology clinic to directly verify patient skin doses. Moreover, existing CT dose measures such as the Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP) as displayed on the MSCT scanner console do not directly relate to patient dose.
The objective of the following thesis is to investigate if the MOSkin dosimeter, based on real-time MOSFET technology, developed at the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong, Australia, may be applied in clinical diagnostic x-ray CT photon beams as a CT radiation dosimeter.
The main contributions of this thesis were firstly, the use of Monte Carlo simulations with the GEANT4 Toolkit to characterise the energy response of a prototype MOSkin dosimeter at clinical kilovoltage x-ray photon energies. Further simulation studies with the GEANT4 Toolkit found that the addition of a composite metallic foil or a change in the thickness of the overlying polyamide layer from the initial MOSkin design resulted in an energy independent radiation sensor. Secondly, a comprehensive experimental characterisation of the MOSkin dosimeter was performed in this work which led to the application of the MOSkin in three separate experimental studies in diagnostic CT radiology. The first experimental application was the acquisition of CT beam profiles through the combined use of the MOSkin dosimeter and the CMRP Dose Magnifying Glass (DMG). The second study applied the MOSkin dosimeter to radiation protection verification for the female breast. The third study was the application of the MOSkin dosimeter for point organ dose measurements in a tissue-equivalent adult anthropomorphic phantom leading to the derivation of effective dose.
The MOSkin has been shown to be a reliable and robust quality assurance tool for the measurement of the range of doses normally associated with x-ray CT scans. It is recommended, based on the results of this thesis, that the MOSkin is used as a dosimetry tool in the radiology clinic for CT quality assurance and organ point dose measurements. In addition, the potential for real-time patient skin dose monitoring in the radiology clinic, not previously possible with the existing generation of dosimeters, is now possible with the MOSkin dosimeter.