Inclusion Criteria:

- Patients must have a histologically confirmed diagnosis of lymphoma expressing the
cluster of differentiation (CD)20 antigen and generally must have failed at least one
prior standard systemic therapy; the exception will be mantle cell lymphoma (MCL)
patients, who may be enrolled while in first complete remission (CR) in accordance
with current transplant standard of care for these patients

- Note: Patients with clinically non-transformed follicular lymphomas do not require
repeat biopsies for immunophenotyping since these tumors are uniformly reactive with
the tositumomab antibody

- Patients must have tumor burdens < 500cc by computed tomography (CT) or magnetic
resonance (MRI) volumetric measurements and must not have splenomegaly at the time of
enrollment; splenomegaly will be defined as a spleen volume > 2 standard deviations
of the mean spleen volume to body weight ratio (mean = 3.84 cc/kg, SD = 1.53 cc/kg);
thus, patients with > 6.9cc/kg will be defined as having splenomegaly; patients with
splenomegaly that is thought to be due to G CSF/GM-CSF effect and not due to
lymphomatous involvement of the spleen can been deemed eligible with the approval of
an investigator

- Patients must have normal renal function (creatinine [Cr] < 2.0)

- Patients must have normal hepatic function (bilirubin < 1.5mg/dL), with the exception
of patients thought to have Gilbert's syndrome, who may have a total bilirubin above
1.5mg/dL

- All patients eligible for therapeutic study must have autologous hematopoietic stem
cells (2 x 10^6 CD34+ cells/kg) harvested and cryopreserved

- Patients must have an expected survival of > 60 days and must be free of major
infection

Exclusion Criteria:

- Circulating anti-mouse antibody (HAMA)

- Systemic anti-lymphoma therapy given within 30 days prior to anticipated treatment
date

- Inability to understand or give an informed consent

- Prior radiation > 20 Gy to any critical normal organ (e.g., lung, liver, spinal cord,
or over 25% of red marrow)

- Central nervous system lymphoma

- Other serious medical conditions considered to represent contraindications to
autologous stem cell transplant (ASCT) (e.g., active coronary artery disease,
pulmonary dysfunction [forced expiratory volume in 1 second (FEV1) < 70% expected,
Vital Capacity < 70% expected, diffusing capacity of the lung for carbon monoxide
(DLCO) < 50%, patient on supplemental oxygen], AIDS, etc.)

- Pregnancy

- Prior bone marrow or stem cell transplant

- Presence of circulating lymphoma cells by morphology or flow cytometry (>= 0.1%) at
or near the time of peripheral blood stem cell (PBSC) collection if unpurged PBSC are
to be used

- Southwest Oncology Group (SWOG) performance status >= 2.0

- Unable to perform self-care during radiation isolation

- Patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma/well
differentiated lymphocytic lymphoma (ineligible because these tumors express very low
surface densities of CD20)