OUTLINE: Patients receive rituximab IV on days 1 and 8 of the first course, then on day 1 of courses 2 and 3. Patients receive cyclophosphamide IV over 1-2 hours, doxorubicin IV, and vincristine IV on day 10 of the first course, then on day 3 of courses 2 and 3. Patients receive oral prednisone on days 10-14 of the first course, then on days 3-7 of courses 2 and 3. Treatment repeats every 21 days for 3 courses in the absence of disease progression or unacceptable toxicity. Chemotherapy is followed by radiotherapy administered 5 days a week for 4-5 weeks. Patients are followed every 6 months for two years, and then annually thereafter.