What is skeletal targeted radiotherapy?

Fancy wording. Sounds like a way to explain why using a radioactive isotope of an element that chemically looks like calcium, the hardening mineral in bones. Strontium, samarium, and most recently, radium fit this bill well. Each isotopes vary in the energy and range of dose distribution, and the conjugating agents, toxicty and costs vary as well.
Myeloma treatment. It is a therapy designed to treat malignant cells in the bone marrow by linking radioactive holmium ho166 to an agent that localized to bone.