The question is complex and requires much more information. In general, metastatic brain cancer is more difficult to treat and resolve since by definition it is a seeded form of the disease from some distant primary location. Make sense? So you stamp out the fire up in the brain with radiotherapy today.....the primary tumor reseeds more cancer cells at some time in the future...could be today, tomorrow, whenever, and we re back to square one...or worse....maybe it gets to the other side...more radiotherapy....damage will occur with the therapy itself. So a prognosis on life expectancy is best asked of his treating physicians since they would need what his actual medical status is right now. I wish you the best with your girlfriend s dad. Please rate this with a STAR RATING if the answer was helpful.