I am so sorry with what you are going through. My father had NSCLC that did spread to his brain. He underwent 16 Whole Brain Radiation treatments. What we were told was that 20% of whole brain radiation patients will suffer some form of dimentia within 5 years. We were advised to take that chance even though his brain met was surgically removed. The doctors thought that was his best chance of the brain tumor not returning. My father, unfortunately did suffer from dimentia. He was not the same person within a year, and as the years went on, he became more and more confused, and forgetful. His personality completely changed. We will never know if putting him through the whole brain radiation was the right decision. All I can tell you is that he survived for 4 years after that. His lung cancer came back with a vengence in June and he just passed away 2 1/2 weeks ago.
The internet is loaded with good information. I strongly suggest you do the research on Whole Brain Radiation and discuss your findings with the doctors.
My prayers are with you.