A Study of Response Adapted Ultra Low Dose 4 Gy Radiation for Definitive Therapy of Marginal Zone Lymphoma

Inclusion Criteria: * Patients 18 years or older. Because no RT dosing data are currently available on the use of response adapted ultra low dose RT in patients \<18 years of age, children are excluded from this study. * Patients with stage I-II marginal zone lymphoma. Patients with a pathology report consistent with low grade B cell lymphoma, favor marginal zone lymphoma, are included. Other low grade lymphomas including follicular grade I/II and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) are ineligible. * Patients should not be planned for any systemic therapy before the first follow up evaluation after radiation (intent is to treat with radiation therapy alone). * Patients with biopsy-proven disease treated with another modality (such as systemic therapy) prior to radiation must have clinical or radiographic evidence of residual disease before enrollment. Patients with clinical and/or radiographic masses that are measurable will have dimensions noted prior to therapy. If an excisional biopsy is performed, patients should have clinically or radiographically apparent disease after biopsy (this does not apply to gastric MALT lymphoma patients). * Prior systemic therapy is allowed, as long as administration is prior to most recent disease assessment by imaging, clinical exam, or endoscopy. There are no limits on the nature or amount of prior systemic therapy. * Prior antibiotics intended to treat marginal zone lymphoma are allowed, as long as administra…