Permanent breast seed implant (PBSI) is a novel treatment technique for early-stage breast cancer. Post-lumpectomy, 103Pd seeds are permanently implanted in the patient’s breast as an alternative to standard fractionated whole breast irradiation. In recent years, the use of PBSI has grown internationally with several new clinics beginning to offer this technique to eligible women. In this thesis, we investigate several sources of uncertainty in PBSI post-implant analysis. While permanent implant brachytherapy procedures have been in clinical use in the prostate for several decades, implementation in the breast raised several new questions, particularly due to tissue mobility and different organs-at-risk. The protracted length of time over which the prescription dose is deposited renders this an important question in the context of post-implant analysis. We performed a study investigating the impact of patient arm position on resultant dosimetry, recommending imaging with the patient arm in the treatment position. Furthermore, we created a model of the dose deposition over the first two months post-implant to assess the most appropriate time to perform analysis, recommending approximately 30 days post-implant. To perform rigorous post-implant analysis, a process to reconstruct the implant and compare it to the plan is required. In this work, we developed an optimization algorithm to automate plan reconstruction and calculate indices pertaining to the geometric quality of the implant. This algorithm has also allowed us to analyze post-implant seed migration and assess any needle characteristics that may be predictive of increased migration. Prior to implanting radioactive seeds, quality assurance is performed to ensure the seeds are of an expected activity. In this work, we produced correction factors for air-kerma strength measurement of several seeds due to variations caused by altitude. In this thesis, we have made several recommendations for the performance of PBSI post-implant analysis. These recommendations have helped to improve patient convenience, by reducing their number of visits to the cancer centre; inter-centre consistency, by recommending time points and patient positioning for imaging studies; and facilitate implementation of post-implant analysis into the clinical analysis process.