Microwave imaging is of increasing interest for breast imaging because it is inexpensive, safe, and fast. Previously, tumour detection has been the focus of microwave imaging re- search, however, breast cancer treatment monitoring is a growing area of interest. Microwave imaging is especially well suited for frequent scanning because it does not expose patients to harmful radiation. Currently, there are no clinical imaging methods routinely used to monitor breast tissue during radiation treatment or shortly after. As a result, early indicators of recurrence or fibrosis (the scarring and thickening of tissue) are not measured. In this thesis, we investigate a microwave transmission system developed at the University of Calgary for the application of monitoring breast changes over time. This imaging system scans a region of the breast and creates low resolution images showing the distribution of tissue. Despite the low resolution, the system demonstrates consistency when scanning over time. In this work, the causes for variation between scans and the performance of the system when scanning frequently are further investigated. Furthermore, microwave scans are evaluated for a group of cancer patients undergoing radiation treatment, and changes between treated and untreated breast over time are identified. Finally, a preliminary alignment method between microwave and mammogram images is introduced. Using this method, the features from mammography are related to features in the microwave scans. This thesis provides results that suggest the microwave transmission system can detect breast differences that are consistent with the clinical history of patients.