Additional Study Information: The main goals of this study are to evaluate the safety of the combination of the study drug radium-223 dichloride plus bortezomib and dexamethasone and to determine the optimal dose of radium-223 dichloride to be used in combination with bortezomib and dexamethasone. Radium-223 dichloride has been approved in some countries for treatment of patients with prostate cancer with bone metastases, but has not been approved yet in patients with multiple myeloma. Radium-223 dichloride is a radioactive drug, that is administered through the vein and that is taken up by bones after it is injected into the body. It works by giving off radioactivity, which is thought to kill the tumor cells that have spread to the bone. Radium-223 dichloride mainly releases a type of radioactivity that travels a very short distance. As a result, most of the effects of the drug are limited to the bones, which is the main location where multiple myeloma causes lesions.