Year

2015

Degree Name

Doctor of Philosophy

Department

Centre for Medical Radiation Physics

Abstract

Silicon diodes have been widely used in radiation therapy quality assurance applications because they have a number of attractive qualities, including real-time feedback (compared to film), high spatial resolution, high linearity, radiation hardness and a small size (compared to ionisation chambers). This work describes three dosimetry systems based on silicon detectors that were developed and manufactured at the Centre for Medical Radiation Physics for Quality Assurance in external beam radiation therapy.

The first part of this study is focused on the characterisation of a single pad detector based on a p-type silicon epitaxial layer, used to assemble a 2-D array of diodes, named MagicPlate-121, for dosimetry and fluence measurement of MV photon beams. The single detector has been tested in terms of radiation hardness and its radiation damage mechanism simulated by Technology CAD modelling. The epitaxial detectors were readout by the TERA, application-specific integrated circuit chip designed for ion chambers. The detector showed unusual total dose radiation response as a function of the irradiation dose, and also showed stabilization of the response within ±2.5% for 12 kGy of gamma irradiation dose (Co-60). The photoneutron radiation damage was also tested and showed a decreased response within 0.5%/100 Gy. The EPI detector demonstrated high radiation hardness for used in clinical quality assurance (QA).

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