Combined Immunochemotherapy Followed By Reduced Dose Radiation Therapy (RT) for Patients With Newly Diagnosed Primary Central Nervous System Lymphoma

Inclusion Criteria: * All patients must have a histologic diagnosis of non-Hodgkin's lymphoma by brain biopsy. Patients who have an inconclusive biopsy or who are not candidates for biopsy may be eligible provided they have a typical cranial magnetic resonance imaging (MRI) or computed tomography (CT) scan and meet at least one of the following two criteria: * A positive cerebrospinal fluid (CSF) cytology for lymphoma or a monoclonal lymphocyte population as defined by cell surface markers * A biopsy of the vitreous or uvea demonstrating non-Hodgkin's lymphoma * A typical MRI/CT scan for primary intracranial lymphoma is defined as the presence of hypo, iso, or hyperdense parenchymal contrast-enhancing (usually homogeneously) mass lesion(s) * Patients must be HIV-1 negative * Patients must have a normal or negative pre-treatment systemic evaluation including: * A bone marrow aspirate and biopsy * CT scans of the chest, abdomen and pelvis * Patients must have adequate bone marrow function (defined as peripheral leucocyte count \> 4000 cells/mm3 and platelet count \> 100,000 cells/mm3), liver function (bilirubin \< 2.0 mg and SGOT \< 2 times upper limit of normal), and adequate renal function (serum creatinine \< 1.5 mg/dl or creatinine clearance \> 50 cc/min/1.73M2) * Men and women of reproductive potential must agree to use an acceptable method of birth control during treatment and for six months after completion of treatment Exclusion Criteria: The following would exclude a patient from the study: * Prior cranial irradiation * Other active primary malignancy with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ * Pre-existing immunodeficiency such as renal transplant recipient * Prior treatment with chemotherapy for CNS lymphoma