Master of Science - Research
Faculty of Engineering
Moutrie, Vaughan, Exploration of a virtual MVCT for use in radiation therapy planning, Master of Science - Research thesis, Faculty of Engineering, University of Wollongong, 2014. http://ro.uow.edu.au/theses/4184
Radiation therapy planning systems utilize CT imaging to determine the electron density of patient anatomy and measurement phantoms. The properties of the kilovoltage photons from a CT scanner are different to the megavoltage photons used for treatment on a linear accelerator, meaning that a CT Number to electron density calibration is required. However not all materials have the same CT Number to electron density conversion as it is a complicated relationship, depending on the atomic number, physical density and electron density of the material.
The aim of this work was to develop a technique to identify such materials using the megavoltage X-ray of a linear accelerator and electronic portal imaging device (EPID). The technique uses the pixel values of a single planar image to identify an unknown material that is contained within a known substance, such as a metal prosthesis within tissue. Another use is the accurate determination of the electron density of a phantom material for use in dosimetry measurements. Simple, homogeneous phantoms were measured to within 3 % of their reported electron density. The identification of an inner portion of a multi-part phantom was also successful, with reported values matching the measured results within experimental uncertainty.