Breast conserving therapy for women with breast cancer consists of local excision of the tumour (achieving clear margins) followed by radiation therapy (RT). RT is given to sterilize tumour cells that may remain after surgery to decrease the risk of local tumour recurrence. Most true recurrences occur in the same quadrant as the original tumour. Whole breast RT may not protect against the development of a new primary cancer developing in other quadrants of the breast. In this Cochrane Review, we investigated the role of delivering radiation to a limited volume of the breast around the tumour bed (partial breast irradiation: PBI) sometimes with a shortened treatment duration (accelerated partial breast irradiation: APBI).