Doctor of Philosophy
Department of Engineering Physics
Bradley, Peter D., The development of a Novel Silicon Microdosimeter for high LET radiation therapy, Doctor of Philosophy thesis, Department of Engineering Physics, University of Wollongong, 2000. http://ro.uow.edu.au/theses/1367
This work is the first comprehensive investigation of the issues confronting silicon microdosimetry and its application to radiotherapy. Four main problems requiring investigation are identified and addressed including requirement specification with particular emphasis on device shape, tissue equivalence, noise minimization, andsensitive volume definition.
Analysis of device shape showed that a rectangular parallelepiped with a tissue equivalent converter on top of device (i.e. a silicon microdosimeter) provides a lineal energy spectrum that is closely equivalent to a sphere using the criteria of equal dose mean lineal energy. The tissue equivalent study demonstrated that under appropriate geometrical scaling (dimensions multiplied by 1/0.63) silicon detectors with well known geometry will record energy deposition spectra representative of tissue cells of equivalent shape. A novel prototype device using silicon-on-insulator (SOI) is presented. Silicon-on-insulator technology assists in defining the sensitive volume depth although the current device still suffers from lateral diffusion effects. I-V and C-V testing are performed and a noise optimization design model is presented. Methods for characterizing the collection efficiency and radiation hardness of silicon microdosimeters are presented and compared including alpha and proton microbeam spectroscopy, broadbeam alpha spectroscopy and 2D and 3D device simulation.
Results from testing the low noise prototype SOI device at several high LET clinical facilities including BNCT, proton therapy and fast neutron therapy facilities are presented. In the BNCT experiments, a simultaneous thermal neutron flux and microdosimetric measurement at a high spatial resolution is demonstrated. The use of SOI technology in experimental microdosimetry offers simplicity (no gas system or HV supply), high spatial resolution, low cost, high count rate capability and the possibility of integrating the system onto a single device with other detector types. The device also offers applicability in radiation protection and electronic single event upset (SEU) studies.