A radioisotope is a version of a chemical element that has the same number of protons characteristic of the chemical element but varies in terms of the number of neutrons in its atoms. Different isotopes of an element may have different radioactivities. A radioisotope is one that is radioactive. Radioisotopes are used for diagnostic and treatment purposes. Radioisotopes have been examined for their effectiveness in patients with cancer for pain control from bone metastases.