Usually, radiotherapy is only offered as a curative treatment e.g to men who have no spread. so that sounds like good news for your dad. Are you sure it was a bone marrow test though? That would be very unusual so I wonder if he got a bit muddled and has actually had a bone scan instead? That would be fairly routine, and almost all men are sent for an MRI scan when they are diagnosed.
So dad is probably panicking unnecessarily but I think if you really can't go to his next appointment with him it would be a good idea to ask dad to go to his GP and request copies of the specialist's letters and the diagnosis details so that you can read them and get the facts.