Multiple myeloma is a disease that resides primarily in the bone and has shown to be sensitive to radiation. Administration of a radiotherapy agent that targets the bone, such as Holmium-166-DOTMP, in conjunction with melphalan and an autologous stem cell transplant, may improve the patient's chance of responding to treatment. The purpose of this study is to determine the amount of Holmium-166-DOTMP that localizes in the bone and in normal organs, and to evaluate the safety and efficacy of Holmium-166-DOTMP in the treatment of patients with multiple myeloma.