- Regimen B (rituximab and IVAC chemotherapy): Patients receive rituximab** IV on day 1, ifosfamide IV continuously and etoposide IV continuously over 24 hours on days 1-5, and high-dose cytarabine IV over 1-3 hours twice daily on days 1-2. Patients receive CNS prophylaxis comprising methotrexate IT and hydrocortisone IT on day 5. Patients also receive pegfilgrastim SC once 24-48 hours after completion of chemotherapy OR G-CSF SC beginning on day 6 and continuing until blood counts recover.