Year

2020

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

A major problem for radiation therapy of lung cancer is respiration-induced motion, which causes both the tumour and surrounding normal tissue to move during treatment. This motion often results in inadequate target coverage and increases the likelihood of additional healthy tissue exposure; therefore detracting from the therapeutic benefits and increasing the risk of radiation induced toxicity. Some motion-management techniques include additional treatment margins to encompass the range of tumour motion, monitoring the respiratory cycle and treating only when in a particular phase i.e. respiratory gating, or imaging the tumour during treatment and adapting the radiation beam aperture to follow the tumour i.e. image guidance and tracking.

Magnetic-Resonance-Imaging (MRI)-linacs are a form of image guided radiotherapy, these systems offer high soft-tissue contrast imaging (with MRI) while simultaneously treating with a therapeutic radiation beam (linear accelerator or linac). The effects of the magnetic field on dose deposition and detector response should be well understood to safely translate this technology to clinical treatments. For MRI-linacs where the magnetic field is inline with respect to the beam, the effects of the magnetic field on electron trajectories in lung can be significant and therefore it is important to study the impacts of this on dose distribution in order to treat lung SBRT on these systems.

In this thesis, a 4D Monte Carlo dose calculation tool is developed and implemented for assessing current radiotherapy techniques for lung Stereotactic Body Radiotherapy (SBRT). In recent years there has been an increasing interest in MRI-guided radiotherapy and its potential to be used for lung SBRT. With the higher doses per fraction used for SBRT there is an increased need for highly accurate dose calculations and localised delivery; particularly for MRI-linac lung treatments, where the magnetic field strongly influences lung tissue and tumour dose distributions. This thesis also presents work towards translating the 4D Monte Carlo method for inline MRI-linacs.

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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.