Student Number : 8802466H - MSc research report - School of Physics - Faculty of Science / Medical ionising radiation sources give by far the largest contribution to the population dose from man-made sources. About 90% of this contribution is due to x-ray diagnostic procedures. Doses from diagnostic radiology procedures are nevertheless small and usually do not approach thresholds for deterministic effects. However, they must be accurately determined in order to maintain a reasonable balance between image quality and patient exposure. There is, thus, a need to establish quality assurance for diagnostic procedures that will provide the required clinical information in its optimal form and with minimum dose to the patient. In order to achieve this, dose measurements must be reproducible and the uncertainties associated with that measurement should be known. One of key factors for ensuring that appropriate levels of accuracy and long-term reproducibility of dose measurements are maintained is a calibration of the measuring equipment. The IEC (International Electrotechnical Commission) issued a standard IEC 61267 that deals with methods for generating radiation beams with radiation conditions which can be used under test conditions typically found in test laboratories for the determination of characteristics of medical diagnostic X-ray equipment. The document is currently being revised and publication of the new version is expected soon. Standard radiation qualities were established at a laboratory following the new IEC 61267 standard. Radiation qualities that characterize radiation beams emerging from the X-ray target (RQR qualities) were established. They were further filtered by Copper to obtain RQT beam qualities that simulate those used in Computed Tomography (CT). The spatial uniformity of a commercial CT dosimeter was then determined.