Feasibility Study of External Beam Radiotherapy and Iodine-131 Tositumomab (Bexxar) for Patients With Relapsed Follicular Non-Hodgkin's Lymphoma
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.
Interventional
Endpoint Classification: Safety Study, Intervention Model: Single Group Assignment, Masking: Open Label, Primary Purpose: Treatment
The Primary Endpoint of the Study Will be to Determine the Feasibility of Combining External Beam Radiotherapy (EBRT) and Bexxar by Assessing the Toxicities Associated With the Treatment.
13 patients will be enrolled initially and followed for 3 months. If less than 10 of these patients reach a grade III or IV toxicity, then 12 more patients will be enrolled and the study will be deemed feasible. If 11 or more of the first group experience grade III/IV toxicity, the trial will stop early.
2 yr 3 mos
Yes
Robert J Amdur, MD
Principal Investigator
University of Florida
United States: Institutional Review Board
GSK Protocol #109407
NCT00475332
September 2007
April 2009
Name | Location |
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University of Florida | Gainesville, Florida 32610-0277 |