A Phase II Study of Iodine-131 Labeled Tositumomab in Combination With Cyclophosphamide, Doxorubicin, Vincristine, Prednisone and Rituximab Therapy for Patients with Advanced Stage Follicular Non-Hodgkin's Lymphoma

--Previously untreated Stage III, IV, or bulky Stage II follicular B-cell NHL, which is positive for CD20.
--Must be age 18 or older.
--Must have a performance status of 0, 1, or 2.
--Must have bidimensionally measurable disease.
--Adequate sections from the original biopsy specimen must be available for pathology review.
--Must have a unilateral or bilateral bone marrow asp/biopsy w/in 42 days prior to registration unless a positive bone marrow asp/biopsy was done within 6 months prior to registration.
--Must have a diagnostic CT scan of chest and abdomen/pelvis w/in 28 days prior to registration. PET/CT scan is allowed if CT is of diagnostic quality and contrast enhanced.
-Must have a cardiac ejection fraction >/= 45% by MUGA or ECHO w/ no significant abnormalities w/in 42 days prior to registration.
--Must not have prior malignancy except adequately treated basal cel or squamous cell skin cancer, in situ cervical cancer, adequately treated Stage I or II cancer from which patient is in CR, or any other cancer from which patient is disease free for >/= 5 yrs.
--No prior chemotherapy, RT, or antibody therapy for lymphoma.
--Must not be pregnant or nursing.
--Must not be HIV positive or have a history of solid organ transplantation. Patients at high risk of Hepatitis B virus (HBV) infection are eligible.
--Must not be requiring continuous supplemental oxygen therapy.
--Must not have clinical evidence of CNS involvement by lymphoma.