Degree Name

Doctor of Philosophy


School of Physics


A large area pixelated silicon array detector named \MP987" has been developed for in-vivo dosimetry. The detector was developed to overcome the non-water equivalent response of EPID (Electronic Portal Imaging Device) dosimetry systems, due to the shortfalls of the extensive corrections required. The detector, readout system and software have all been custom designed and operate independently from the linac. The MP987 array is secured directly above the EPID, to be used in combination with the 6 MV imaging system.

During the course of this thesis many aspects of in-vivo dosimetry were looked at, including: electrical and dosimetric characteristics of silicon diodes, feasibility of a dual detector system, angular dependence of silicon and synthetic diamond detectors and the suitability of different detector readout systems for multichannel arrays in external beam radiotherapy.

In the final chapter of this thesis dosimetry characterisation measurements of percentage depth dose (PDD), dose rate dependence, radiation damage, output factors (OF), profile measurements, linearity and uniformity were performed with the MP987. Additionally, the first pre-clinical tests with this novel detector are presented, including, a transit dosimetry characterization and a collapsed IMRT (intensity modulated radiation therapy) study. Both PDD and OF measurements had a percentage difference of less than 2.5% to the reference detector. A maximum change in sensitivity of 4.3 ± 0.3% was observed after 30 kGy of gamma accumulated dose. Transit dosimetry measurements through a homogeneous phantom had a measured dose within the uncertainty of the TPS calculations, for field sizes between 3 × 3 cm2 and 10 × 10 cm2. A four-fraction collapsed IMRT plan on a lung phantom had absolute dose pass fractions between the MP987 and TPS (treatment planning system) from 94.2% to 97.4%, with a 5%/5 mm criteria. The ability to accurately measure dose at a transit level, without the need for correction factors derived from extensive commissioning data collection procedures, makes the MP987 a viable alternative to the EPID for in-vivo dosimetry. This MP987 is this first of its kind to be successfully developed specifically for a dual detector application.

FoR codes (2008)




Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.