Partial breast irradiation (PBI) is becoming more widespread in the treatment of early breast cancer in patients at low risk of relapse as pathological and clinical findings have demonstrated that most breast cancer recurrences after BCS occur close to the tumour bed. In our phase II prospective study PBI is administered with high-dose-rate brachytherapy in patients with low-risk early-stage breast cancer. Patients receive 4 Gy twice a day for 4 days (total dose 32 Gy).