Year

2018

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

Breast cancer is a main health problem throughout the world and it is the major cause of death from cancer among female worldwide. One in ten of all new cancers diagnosed annually in both developed and developing countries is a cancer of the women breast. Based on the national statistics on breast cancer in Australian women, 37 females on average were diagnosed with breast cancer daily in 2008. Radiation therapy plays a major part in the management of breast cancer. It results in both enhanced survival rates and increased local control of the cancer.

There are three main parts within this thesis. The first part focusses on the dosimetric characterizations study, which was performed for the of the newly developed n-type Skin diode dosimeter with 7 μm thick epitaxial layer for in vivo skin dosimetry for external beam breast treatments. The Silicon Diode showed a feasible response to different field sizes, radiation incident angles, PDD, output, entrance and exit dose measurements. The percentage entrance doses, as measured by the Skin diode, were slightly higher than doses for water equivalent depth (WED) 0.07 mm, which will be corrected through a re-engineering of the top encapsulating layer through subsequent updates of the design. The Skin diode may provide a good possibility for real-time in vivo skin dosimetry during external photon beam radiation therapy.

The second part of this thesis provides the investigation, which was done to study the feasibility of using the brass mesh bolus as an alternative to tissue- equivalent (TE) bolus for post mastectomy chest wall cancer. In this part, the dosimetric characterizations of the 2-mm fine brass mesh bolus was performed. In particular, the effect of brass bolus on dose build-up at the entrance surface, the beam exit, surface dose and beam profiles and percentage depth doses were evaluated. The cases of the bolus, which were used in this area, are Face-up brass bolus, Face-down brass bolus, double brass bolus and TE-Superflab bolus. These measurements were done in RW3 slab phantom and curved phantom as a precursor curved contour. It was found that the brass mesh bolus does not significantly change dose at depth (less than 0.5%), and the surface dose is increased compared to TE bolus. Considering this, brass mesh may be used as a substitute for TE bolus to increase superficial dose for chest wall tangent plans. However, the effect of the mesh on surface and superficial dose when used in conjunction with tangential irradiation geometries is complicated and requires careful consideration before clinical use.

The final part in this thesis focusses on the examination that done to investigate the feasibility of determining the real-time in vivo breast skin dose by monitoring doses during treatment and also to measure the effects of setup errors and changes in patient geometry on the epidermal skin dose using the MOSkinTM dosimeter for a range of techniques, including 3D-CRT, IMRT and VMAT. Thus, allowing the stability of epidermal skin dose to be compared between planning techniques of different complexity.

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