Can radiation therapy help treat lung cancer metastases to the liver and bones?

Yes. Radiation is often used to alleviate many symptoms from cancer that has spread to organs and that includes liver and bone. Not every spot involved has to be treated only those causing some sort of problem. If the patient only has one small liver metastasis for example more aggressive treatment with radiosurgery can be considered.
Yes. Radiation can be a very effective palliative treatment. It can be used on any site in the body. Whether radiation is appropriate for any given particular case should be discussed in consolation with your radiation oncologist.