Radiation therapy uses high-energy rays (x-rays) to kill malignant plasma (myeloma) cells and it may be used to treat myeloma patients in select circumstances. Radiation therapy is the main treatment for plasmacytoma. Carefully selected patients whose bone pain does not respond to chemotherapy may receive radiation therapy as well. Radiation therapy may be impractical if there are widely distributed sites of painful bone involvement. Other means of delivering radiation therapy are under investigation, such as by attaching a radioactive isotope to a molecule that goes predominantly to the bones, where most myeloma is located.