Feasibility Study of External Beam Radiotherapy and Iodine-131 Tositumomab (Bexxar) for Patients With Relapsed Follicular Non-Hodgkin's Lymphoma
Feasibility Study of External Beam Radiotherapy and Iodine-131 Tositumomab (Bexxar) for Patients With Relapsed Follicular Non-Hodgkin's Lymphoma
The purpose of this study is to determine the feasibility of treating relapsed follicular lymphoma with a combination of Bexxar and External Beam Radiotherapy (EBRT). Patients will receive EBRT (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 Non-Hodgkin's Lymphoma (NHL). The basic principle is that larger nodal masses require increased doses of External Beam Radiotherapy (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 (PMID:11418315). He showed that tumors ≥15 cm^3 received only 1082 cGy with Zevalin, whereas the average dose delivered in tumors <15 cm^3 was 4763 cGy. Recently, Gokhale et al (PMID: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 Non-Hodgkin's Lymphoma (NHL), Koral et al (PMID: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 (PMID:10994741). The most compelling data for this relationship comes from the clinical trials done using Bexxar. Both in the pivotal trial (PMID:11579112) and the recently published trial treating naïve patients (PMID: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 central lymphatic irradiation, 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 (NHF). 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 follicular lymphoma.
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 World Health Organization (WHO) criteria
Acceptable hematologic status within two weeks prior to patient registration, including:
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