The purpose of this study is to determine the feasibility of treating relapsed follicular lymphoma with a combination of Bexxar and EBRT. Patients will receive External Beam Radiation Therapy (20 Gy in 10 fractions) followed by Bexxar.

Total dose delivered and tumor size are important predictors of local control in the treatment of low-grade NHL. The basic principle is that larger nodal masses require increased doses of EBRT to achieve local control. Radioimmunotherapy (RIT) seems to share this same characteristic. Review of the published literature on both Bexxar and Zevalin reveals that one of the most important predictors of treatment failure is nodal volume and its apparent relationship to dose delivered by RIT. The best tumor dosimetry for RIT is from Dr. Wiseman et al reporting on the dosimetry of Zevalin (11418315). He showed that tumors ≥15 cm3 received only 1082 cGy with Zevalin, whereas the average dose delivered in tumors <15 cm3 was 4763 cGy. Recently, Gokhale et al (16111589) published their experience with Zevalin at Cleveland Clinic and showed a significant correlation with pretreatment tumor volume and response to therapy. In their experience, tumors ≥5 cm had an 83% rate of local recurrence versus 28% for tumors <5 cm. This dosing paradox (bigger masses, which require more dose, receive less with RIT) may be diminished by the delivery of additional EBRT. This is the hypothesis that underlies the pilot study.

The dosimetric data available for Bexxar is more heterogeneous but confirms the observations seen with Zevalin. In patients previously untreated for low-grade NHL, Koral et al (12621015) showed an increased likelihood of achieving a complete response (CR) if tumor doses were >650 cGy. Previous work by these same authors showed a trend for larger tumor volumes receiving less dose (10994741). The most compelling data for this relationship comes from the clinical trials done using Bexxar. Both in the pivotal trial (11579112) and the recently published trial treating naïve patients (15689582), tumor volume was a significant predictor of response to Bexxar. In the pivotal trial, smaller tumor burden was the only factor predicting longer duration of response.

Whereas EBRT might be able to provide reliable radiation dose, the use of Bexxar may provide the therapeutic equivalent of CLI, which would permit the use of true involved field radiotherapy. Investigators have previously noted that increased EBRT field size is associated with increased short-term and long-term toxicity. The toxicities associated with the treatment of radiotherapy are related to the site treated, but do not necessarily include the dose limiting toxicity of Bexxar, which is primarily hematologic and transient. As the toxicity of RT and Bexxar may not overlap, the combination of both may allow an increase in the therapeutic window for both radiotherapy and Bexxar therapy.

Inclusion Criteria

• Relapsed Stage I-IV (no evidence of bone marrow involvement) Follicular Non- Hodgkin's Lymphoma. Patients must have received at least 1 prior therapeutic regimen of chemotherapy or Rituximab and demonstrated progression as demonstrated by biopsy.
• One or more of the relapsed sites must be 5 cm or greater in dimension as assessed on two dimensional imaging from CT or MRI scan.
• Biopsy at time of relapse confirming continued presence of CD 20 positive FL.
• No anti-cancer therapy for 3 weeks (six weeks if Rituximab, nitrosourea or Mitomycin C) prior to study initiation, and fully recovered from all toxicities associated with prior surgery, chemotherapy, or immunotherapy.
• An IRB-approved signed informed consent.
• Expected survival rate greater than 3 months.
• Prestudy performance status of 0 or 1 according to the WHO criteria

• Acceptable hematologic status within two weeks prior to patient registration, including:

  • Absolute neutrophil count ([segmented neutrophils + bands] x total WBC) greater than 1,500/mm3
  • Platelet counts greater than 100,000/mm3
• Female patients who are not pregnant or lactating.
• Men and women of reproductive potential who are following accepted birth control methods (as determined by the treating physician, however, abstinence is not an acceptable method).
• Patients previously on Phase II drugs if no long-term toxicity is expected, and the patient has been off the drug for eight or more weeks with no significant post-treatment toxicities observed.

Exclusion Criteria

• Patients with impaired bone marrow reserve, as indicated by one or more of the following:
• Prior myeloablative therapies with bone marrow transplantation (either autologous or allogeneic) or peripheral blood stem cell (PBSC) rescue.
• Platelet count > 100,000 cells/mm3
• Hypocellular bone marrow
• Marked reduction in bone marrow precursors of one or more cell lines (granulocytic,megakaryocytic, erythroid).
• History of failed stem cell collection
• Presence of bone marrow involvement with FL > 25% based on bone marrow biopsy done within 2 months of enrollment.
• Evidence of transformation from original FL to a more aggressive NHL histology.
• Prior radioimmunotherapy.
• All relapsed sites are < 5 cm in dimension as assessed on two dimensional imaging from CT or MRI scan.
• Presence of CNS involvement.
• Presence of primary NHL of bone.
• Patients with HIV or AIDS-related lymphoma.
• Patients with abnormal renal function: serum creatinine > 2.0 mg/dL.
• Patients who have received prior external beam radiation therapy within three months of registration.
• Patients who have received G-CSF or GM-CSF therapy within two weeks prior to treatment.
• Serious nonmalignant disease or infection which, in the opinion of the investigator and/or the sponsor, would compromise other protocol objectives.
• Major surgery, other than diagnostic surgery, within four weeks.
• Presence of anti-murine antibody (HAMA) reactivity.