Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed CD20-positive B-cell non-Hodgkin's lymphoma (NHL), including
any of the following subtypes:

- Indolent NHL, including any of the following:

- Follicular

- Lymphoplasmacytoid

- Marginal zone

- Mantle cell NHL

- Transformed B-cell NHL

- In at least first relapse with an indication for systemic antineoplastic treatment,
as defined by the following:

- Local or constitutional (B-) symptoms

- Hypersplenism due to splenic involvement

- Bulky disease (> 7.5 cm in diameter)

- Impending medical problems derived from rapid disease progression within the
past 6 months, as defined by an observed or anticipated > 50% increase in the
sum of the areas calculated from multiplying the greatest perpendicular
diameters of each lesion

- Measurable lesions of lymphoma infiltration

- Medically ineligible for high-dose treatment followed by autologous stem cell support

- Adequate bone marrow cellularity (> 15% of marrow area covered by hematopoiesis)

- No CNS, leptomeningeal, spinal cord, or testes lymphoma involvement

- No lymphoma lesion mandating emergency radiotherapy

- No clinical, cytological, cytogenetic, or histopathologic indication of
myelodysplastic syndrome

- If there is bone marrow infiltration detected prior to chemoimmunotherapy, patient
must undergo a repeat bone marrow biopsy prior to planned treatment with
radioimmunotherapy to verify the level of bone marrow infiltration is < 25%

PATIENT CHARACTERISTICS:

- ECOG performance status 0-2

- Life expectancy ≥ 3 months

- Absolute neutrophil count > 1,500/mm³

- Platelet count > 150,000/mm³

- Hemoglobin > 9 g/dL

- Creatinine < 1.5 times upper limit of normal (ULN)

- Bilirubin < 2 times ULN

- ALT and AST < 2 times ULN

- Albumin > 2.5 g/dL

- INR < 1.5

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for ≥ 12 months after
completion of study treatment

- No concurrent severe and/or uncontrolled medical disease that would preclude study
compliance, including any of the following:

- Uncontrolled diabetes

- Congestive heart failure

- Chronic renal disease

- Active uncontrolled infection

- No bleeding risks or disorders, including any of the following:

- CNS abnormalities suggesting an increased susceptibility for hemorrhage,
including recent history of stroke as demonstrated by cranial contrast-enhanced
CT scan

- Severe arrhythmia or uncontrolled hypertension

- Myocardial infarction within the past 6 months

- Diabetic retinopathy with history of symptomatic hemorrhage

- Known and potentially active gastrointestinal bleeding foci

- Concurrent anticoagulant medication that must be continued even with platelet
count < 20,000/mm³ (e.g., following mitral valve replacement, anti-phospholipid
syndrome, or recurrent venous thromboembolism)

- Other congenital or acquired hemorrhagic diatheses

- No ongoing autoimmune hemolytic anemia

- No known presence of anti-murine antibody reactivity

- No known hypersensitivity to murine or chimeric antibodies or proteins

- No known HIV infection

- No psychiatric illness that would preclude study requirements

- No other malignant disorder within the past 10 years except basal cell carcinoma of
the skin or carcinoma in situ of the cervix

PRIOR CONCURRENT THERAPY:

- See Disease Characteristics

- Recovered from prior therapy

- No more than 4 prior systemic anti-lymphoma regimens (including single-agent
rituximab)

- At least 2 months since prior systemic anti-lymphoma treatment (including
single-agent rituximab)

- No prior radioimmunotherapy

- No prior autologous or allogeneic hematopoietic stem cell transplantation

- No prior treatment with purine analogues that has not resulted in remission for > 1
year

- No prior anti-CD20 radioimmunoconjugate therapy

- More than 5 years since prior radiotherapy to extensive fields covering lymph node
regions on both sides of the diaphragm or > 50% of the spinal column

- More than 4 weeks since prior surgery

- No concurrent oral anticoagulant therapy