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

RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. It is not yet known if giving radiation therapy after stem cell transplantation is more effective than stem cell transplantation alone in treating relapsed or refractory non-Hodgkin's lymphoma. PURPOSE: Randomized phase III trial to determine the effectiveness of radiation therapy in treating patients who have relapsed or refractory non-Hodgkin's lymphoma and have undergone autologous stem cell transplantation.