Patients will be enrolled in cohorts and will be treated at sequentially rising dose levels of AGuIX combined with whole brain radiation therapy. Three subjects will initially enter at each dose. If none of the three experiences a dose-limiting toxicity we will proceed to the next dose. If one of the three experiences that level of toxicity, we will accrue 3 more subjects at that dose. If at any time there are two or more dose-limiting toxicities (in the 3-6 subjects) on a given dose, we will drop down to a lower dose. Dose escalation will continue until the MTD of AGuIX and whole brain radiation therapy is established. The MTD will then be one dose below the DLT occurring in at least 1 out of 3 subjects (2 out of 6 patients).