Radiation Therapy in Relapsed or Refractory Non-Hodgkin's Lymphoma Who Have Undergone Stem Cell Transplantation

DISEASE CHARACTERISTICS: * Histologically confirmed non-Hodgkin's lymphoma * Diffuse large cell lymphoma, B-cell (includes primary mediastinal B-cell lymphoma and T-cell rich B-cell lymphoma) * Previous indolent lymphoma (follicular center cell lymphoma, marginal zone lymphoma, including extranodal MALT lymphoma and lymphoplasmacytoid lymphoma) with transformation to diffuse large B-cell lymphoma at relapse * Peripheral T-cell lymphoma * Anaplastic large cell lymphoma (T cell or null cell) * Small non-cleaved Burkitt-like lymphoma * Relapsed or refractory disease after first-line anthracycline-based chemotherapy * Bulky disease, nodal or extranodal * Clinically or radiographically measurable mass at least 5 cm in diameter OR * Non-bulky disease, nodal or extranodal, excluding diffuse organ (lung, liver, kidney, or bone marrow) involvement * Clinically or radiographically measurable disease more than 1.5 cm in greatest transverse diameter * Biopsy at relapse not required except for transformed lymphomas * Patients with transformed lymphoma at diagnosis, but with indolent histology without transformation at relapse, are not eligible * No patients with stage IA or IIA disease at initial diagnosis who, at time of relapse or diagnosis of refractory disease prior to salvage therapy, remained in stage IA or IIA, with no new disease sites, without having received radiotherapy * Received up to 2 regimens and 4 courses of salvage chemotherapy * Monoclonal antibodies (e.g., rituximab) are not considered salvage chemotherapy * Achieved complete response (CR), unconfirmed CR, or partial response (PR) if bulky disease OR * Achieved PR (but not CR) if non-bulky disease * No residual disease involving extranodal organs diffusely (e.g., liver, lung, bone, kidney, or leptomeningeal) after salvage chemotherapy * Planned autologous hematopoietic stem cell transplantation (ASCT) * ASCT conditioning must be with high-dose BEAM (carmustine, etoposide, cytarabine, and melphalan) chemotherapy * No disease progression after ASCT * No major organ complication or poor hematologic recovery from ASCT that would preclude initiation of study radiotherapy within 14 weeks after ASCT * No more than 2 non-contiguous nodal or extranodal areas of bulky/residual disease requiring more than 2 separate involved-field radiotherapy volume arrangements (e.g., field arrangement covering up to 2 involved lymph node regions or extranodal sites, with or without 1 adjacent nodal/region or extranodal site) * No active CNS lymphoma (parenchymal brain and/or leptomeningeal) PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * ECOG 0-2 Life expectancy: * Not specified Hematopoietic: * Not specified Hepatic: * Not specified Renal: * Not specified Other: * Not pregnant or nursing * Fertile patients must use effective contraception * No other malignancy within the past 5 years except basal cell carcinoma of the skin PRIOR CONCURRENT THERAPY: Biologic therapy: * See Disease Characteristics * No prior radioimmunotherapy Chemotherapy: * See Disease Characteristics Endocrine therapy: * Not specified Radiotherapy: * See Disease Characteristics * No prior total body irradiation * No prior radiotherapy to the site of bulky disease or residual tumor Surgery: * Not specified Other: * No other concurrent anti-cancer therapy unless documentation of disease progression