Year

2001

Degree Name

Doctor of Philosophy

Department

Department of Engineering Physics

Abstract

Radiation oncology is an important part of cancer therapy. In 1996 a Committee of the Australian National Health and Medical Research Council recommended that 50-55% of all the new cancers include radiotherapy as part of their treatment. Cancer patients are treated with different radiation oncology modalities and while most are treated by conventional x-ray therapy a growing number is treated by hadron therapies such as fast neutron therapy (FNT), brachytherapy, proton therapy, heavy ion therapy and boron neutron capture therapy (BNCT). A new radiation oncology modality, microbeam radiation therapy (MRT), is currently under development. The outcome of radiation treatment in a hadron therapy is highly dependent on an accurate knowledge of both dose distribution and the quality of the radiation beam.

Aim of this project was to develop new semiconductor probes for applications in hadron therapy and in synchrotron M R T and for validation of quality assurance on these modalities.

A. Metal oxide semiconductor field effect transistor (MOSFET) dosimeters have been investigated in this study and new applications for dosimetry in radiation oncology have been introduced.

• A novel dual use of a MOSFET detector has been proposed, which is based on simultaneous mini and microdosimetry by a single M O S F E T detector.

• The count mode response of a M O S F E T detector has been investigated for correlation with its integral response in a high lineal energy transfer (LET) radiation field for separation, by a single M O S F E T detector, of low and high L E T doses in a mixed radiation field.

• A paired integral M O S F E T detector technique, for dosimetry in a thermal neutron field, has been proposed and investigated. This technique has allowed determination of a relative boron depth dose in B N C T and evaluation of the boron enhancement in F N T.

• A novel "edge-on" M O S F E T mini dosimetry has been introduced, investigated and its micron scale spatial resolution proven. It was successfully demonstrated that the "edge-on" M O S F E T probe can be used for accurate measurements of the dose profile of a 30 urn wide synchrotron microbeam for MRT.

• The role of a M O S F E T package for detector response was investigated for xray beams with energy range from 20 keV to 6 M V .

• High spatial resolution M O S F E T dosimetry, in strong electron nonequilibrium x-ray fields of a conventional medical linac, has been proved using optimal packaging.

B. A pulse method has been introduced for neutron clinical dosimetry

• A small sized ion-implanted silicon detector with a thick 23 U converter, for absolute thermal neutron dosimetry, has been theoretically simulated and developed.

• Successful applications of the probe for thermal neutron flux and boron dose measurements in B N C T , F N T and californium-252 brachytherapy have been demonstrated with thermal neutron flux measurements being within 5% agreement with Monte Carlo calculations.

The semiconductor probes that have been developed during this project are accurate, reliable, have a high spatial resolution, require low operating voltage, are of low cost, versatile and offer significant advantages when compared with conventional detectors currently in use in radiation oncology.

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