Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed indolent non-Hodgkin's lymphoma (NHL), including 1 of the
following histologic subtypes:

- Grade1 or 2 follicular lymphoma

- Small lymphocytic lymphoma (SLL)

- Marginal zone B-cell lymphoma

- CD20-positive disease confirmed by immunohistochemistry or flow cytometry

- Bidimensionally measurable disease

- At least 1 lesion measuring ≥ 2.0 cm in a single dimension by CT scan

- Less than 25% bone marrow involvement with lymphoma by bilateral iliac crest bone
marrow aspiration and biopsy within the past 6 weeks

- No clinically significant impaired bone marrow reserve as evidenced by any of the
following:

- Hypocellular marrow, as evidenced by 1 of the following:

- ≤ 15% cellularity

- Marked reduction in bone marrow precursors

- Platelet count < 100,000/mm^3

- Absolute neutrophil count < 1,500/mm^3

- History of failed stem cell collection

- Prior myeloablative therapy

- No greater than 5,000/mm^3 circulating tumor cells in peripheral blood

- Requires antilymphoma therapy, as indicated by any of the following:

- Systemic symptoms

- B symptoms

- Cytopenias

- Malaise

- Organ compromise

- Discomfort

- Pain

- Disfigurement

- Rapidly progressive disease

- Undue anxiety related to not receiving treatment

- No transformation to intermediate or high-grade NHL

- No known brain metastases or CNS involvement by lymphoma NOTE: A new classification
scheme for adult non-Hodgkin's lymphoma has been adopted by PDQ. The terminology of
"indolent" or "aggressive" lymphoma will replace the former terminology of "low",
"intermediate", or "high" grade lymphoma. However, this protocol uses the former
terminology.

PATIENT CHARACTERISTICS:

Age

- Over 18

Performance status

- ECOG 0-2 OR

- WHO 0-2 OR

- Karnofsky 70-100%

Life expectancy

- More than 3 months

Hematopoietic

- See Disease Characteristics

- WBC ≥ 3,000/mm^3

- Absolute neutrophil count ≥ 1,500/mm^3

- Platelet count ≥ 100,000/mm^3

- Lymphocyte count < 5,000/mm^3 (for patients with SLL )

Hepatic

- Bilirubin ≤ 2.0 mg/dL

- AST and ALT ≤ 2.5 times upper limit of normal

Renal

- Creatinine ≤ 2.0 mg/dL OR

- Creatinine clearance > 60 mL/min

Cardiovascular

- No symptomatic congestive heart failure

- No unstable angina pectoris

- No cardiac arrhythmia

Immunologic

- No anti-murine antibody reactivity (in patients with prior exposure to murine
antibodies or proteins)

- No ongoing or active infection

- No history of allergic reaction attributed to compounds of similar chemical or
biologic composition to yttrium Y 90 ibritumomab tiuxetan

Other

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for at least 1 year
after study treatment

- No other active malignancy except non-melanoma skin cancer

- No other serious nonmalignant disease that would preclude study participation

- No psychiatric illness or social situation that would preclude study compliance

- No other uncontrolled illness

PRIOR CONCURRENT THERAPY:

Biologic therapy

- More than 4 weeks since prior pegfilgrastim

- More than 2 weeks since prior filgrastim (G-CSF) or sargramostim (GM-CSF)

Chemotherapy

- No prior chemotherapy

Endocrine therapy

- Not specified

Radiotherapy

- No prior external beam radiotherapy to > 25% of active bone marrow (involved field or
regional)

Surgery

- More than 4 weeks since prior major surgery except diagnostic surgery

Other

- No prior systemic antilymphoma therapy

- No concurrent combination antiretroviral therapy for HIV-positive patients

- No other concurrent anticancer therapy

- No other concurrent investigational agents

- No other concurrent antilymphoma therapy