A variety of radiopharmaceuticals has been used for systemic therapy to relieve pain from malignancies metastatic to bone, using electron emitting radionuclides either in ionic form or as labels for bone seeking compounds to irradiate locally at sites of metastases. The major complication comes from the absorbed dose to the bone marrow. Therefore, there has been a search for radionuclides with lower energy emissions and correspondingly shorter range in tissue. Some studies have shown that it is possible to delay the onset of new pain sites and perhaps increase life expectancy.