Degree Name

Master of Science - Research


Faculty of Engineering


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.