Can radiation therapy treat bone cancer?

Yes. Some people confuse bone cancer with when another type of cancer spreads to the bone (metastasis). Radiation can help the bone or the pain. As dr. Noga stated true bone cancer such as myeloma or plasmacytoma can also be treated with radiation. Other bone cancers, osteosarcoma or bone tumors may also have a role from radiation but surgery is usually the best for that type of bone cancers.
Can treat myeloma. If bone cancer refers to multiple myeloma, then yes radiation therapy is used to treat myeloma. Usually this is a localized use such as around a pending fracture or there is a single plasmacytoma. It has also been used as total body irradiation in combination with chemotherapy for stem cell transplant. The most common use is to reduce pain quickly and is never curative.
Depends on cancer. Some bone cancers, like ewing's sarcoma and multiple myeloma, are very sensitive to radiation, making it a good treatment option. Others, like osteosarcoma, don't respond well to radiation and radiation is only used as a last resort. When cancer, such as breast or prostate, spreads to bone, radiation is commonly used with good results.