- Regimen A (low-risk disease with no CNS involvement): Patients receive R-CODOX-M chemotherapy comprising rituximab IV over 2-4 hours on days 0 and 8; doxorubicin hydrochloride liposome IV over 30 minutes on day 1; vincristine IV on days 1 and 8; cyclophosphamide IV over 1 hour on days 1-5; and high-dose methotrexate (MTX) IV over 24 hours on day 10. Patients also receive leucovorin calcium IV beginning 36 hours after the start of MTX infusion and continuing every 6 hours until blood levels of MTX are safe. Patients also receive filgrastim (G-CSF) subcutaneously (SC) once daily on days 4-8 in courses 1 and 3 and on days 6 and 7 in course 2. Beginning on day 12, daily G-CSF dosing resumes until blood counts recover. Patients receive CNS prophylaxis comprising cytarabine intrathecally (IT) on day 1 and MTX IT on day 3. Treatment repeats every 28 days for 3 courses in the absence of disease progression or unacceptable toxicity.