Rituximab, Combination Chemotherapy, and 90-Yttrium Ibritumomab Tiuxetan for Patients With Stage I or II Non-Hodgkin's Lymphoma

PRIMARY OBJECTIVES: I. To evaluate the complete response rate (CR) and functional CR rate in patients with previously untreated stage I (with at least 1 risk factor) or stage II CD20+ diffuse large cell lymphoma who receive therapy with R-CHOP followed by 90-Yttrium -Zevalin™. SECONDARY OBJECTIVES: I. To evaluate the time to treatment failure, duration of response, and overall survival in these patients who receive therapy with R-CHOP followed by 90-Yttrium -Zevalin™. II. To evaluate the toxicity of this therapy. III. To evaluate the toxicity of adding involved field radiation therapy \> 12 weeks after Zevalin™ for patients with CT+/PET+ residual masses. TERTIARY OBJECTIVES: I. To evaluate PET scans pre -and post - R-CHOP/Zevalin™ therapy. OUTLINE: R-CHOP (rituximab, prednisone, cyclophosphamide, doxorubicin,vincristine): Patients receive oral prednisone once daily on days 1-5. Patients also receive rituximab IV over several hours followed by cyclophosphamide IV, doxorubicin IV, and vincristine IV over 30-60 minutes on day 1. Treatment repeats every 21 days for 2 courses in the absence of disease progression or unacceptable toxicity. Patients achieving a complete response (CR) after 2 courses receive 2 additional courses. Patients achieving a partial response, uncertain CR, or stable disease receive 4 additional courses. Patients are evaluated 3 weeks after the last course of therapy. Patients with progressive disease go off study. Radioimmunotherapy: Beginning no more than 9 weeks after the reevaluation (or 12 weeks after the last dose of R-CHOP), patients receive rituximab IV on day 1 followed by indium In 111 ibritumomab tiuxetan IV over 10 minutes for imaging studies. Patients then receive rituximab IV followed by yttrium 90-Yttrium ibritumomab tiuxetan IV over 10 minutes on day 8. Radiotherapy: Patients with residual disease by CT scan or positron emission tomography (PET) scan after 12 weeks after radioimmunotherapy undergo conventional involved-field radiotherapy. Patients are followed every 3 months for 1 year, every 4 months for 1 year, every 6 months for 3 years, and then annually for 5 years.