This invention provides a safer and more effective treatment for undesirable tissue masses, especially bone cancer and soft tissue tumors. The method involves a composition for direct administration of a therapeutic, radioisotope formulation nearby or directly into the tissue mass. Administration of the dose for bone cancer may be done through a hole created in the bone using a miniature drill. Delivery of the dose directly into a tumor may be accomplished using microsyringe or a miniature pump capable of accurately delivering microliter amounts of material. A chelating agent capable of removing activity from the bloodstream is also an aspect of this invention.