The goals of this research were to improve upon current methodology of measuring commissioning results in block-phantom geometries, and to determine whether the Monaco TPS could be used for clinical TBI treatment planning. This project spans a variety of different subject areas including radiation dosimetry and medical physics, to software and device engineering and mathematical modelling. Necessary concepts will be introduced in a comprehensive manner in order of their significance which will allow for an understanding of the subject by those without specialist background. Chapter 2 provides an overview of radiation dosimetry, radiation therapy, treatment planning systems and algorithms with the aim of providing an understanding of the methodology for measuring dose, and how different treatment planning algorithms predict dose in a patient. Chapter 3 provides a comprehensive look at the development of a new device (PMD) for measuring radiation dose profiles in TBI conditions. This chapter will overview software development and the validation of the PMD with relevant dosimetry equipment. Chapter 4 presents a discussion on the available processes for the prediction of dose in block and anthropomorphic phantoms within Monaco. Chapter 5 progresses through all linac measurements intended for subsequent comparison to Monaco, these allow us to draw conclusions appropriately. Chapter 6 compares and contrasts TPS modelled results in Chapter 4 with linac measurements in Chapter 5, and discusses the outcomes of the research in terms of whether Monaco can be used for TBI treatment planning clinically, and the effectiveness of the PMD for TBI commissioning.