Patients will receive single-dose preoperative radiotherapy followed by breast conserving surgery (BCS) at 12 months after radiotherapy, as long as follow-up MRI scans show a complete radiologic response. In case of incomplete radiologic response, BCS will be performed at 6 months after radiotherapy. BCS is performed earlier when progressive disease is found on MRI. In the follow-up period between radiotherapy and surgery, tumor response will be monitored using MRI every 3 months. After surgery, patients will be followed up until 10 years after radiotherapy treatment to assess oncological outcomes, toxicity, cosmetic outcome and quality of life.