My dad was diagnosed with bone cancer.he suffered severe pain his last days.he just passed away right after a radiation therapy can this be the cause?

No. : I'm sorry for your loss. Radiation therapy is used to treat bony metastasis which, as you know, can be quite painful. I assume that your father passed away due to the same cancer that spread to his bones. Of course, the best person to ask would be his doctor.

Not likely: Unfortunately for patients whose cancer has spread to the bone, the outlook as far as survival is usually not good. Radiation therapy for this is usually to relieve pain but the result may not be seen for a week or two and the pain relief is usually very good. My condolences on your loss.