 This prospective, randomized study, will compare, through a battery of neuropsychological tests, the cognitive impact of WBRT of 40 Gy in 20 fractions with or without hippocampal avoidance by intensity modulated radiotherapy, in patients presenting with a single operated brain metastasis of breast cancer. If the hippocampal avoidance leads to a significant improvement in cognitive function, this radiotherapy scheme could become the standard postoperative treatment to be proposed to patients presenting the best prognostic factors. This would allow to prevent long-term cognitive deficit, while preserving WBRT benefit on intra-cerebral control. 