Conditioning Regimen IV Busulfan 3.2mg/kg or equivalent pharmacokinetics directed dose once daily as a 3-hour infusion on days -5, -4 and -3 (option 1) or on days -6, -5, -4 (option 2).IV Melphalan 140mg/m2 once on day -2 (for option 1) or day -3 ( for option 2) Maintenance Regimen Oral Lenalidomide 10 mg once daily for 28 days of a 28 days cycle for first three cycles and then dose escalation to 15 mg daily if clinically appropriate to do so.