- Regimen 2 (for patients < 50 years of age and unable to tolerate FTBI due to prior dose-limiting radiotherapy or significant cardiotoxicity): Patients receive a test dose of busulfan on day -10 and then dose adjusted busulfan IV 3-4 times daily on days -9 to -6, melphalan IV on days -5 and -4, and fludarabine phosphate IV on days -5 to -2.