@codym, sorry to hear you're going through this. Yes, I've had radiation to my brain a total of 5 times. The first 4 were to clean up the edges after removing the 3.2cm diameter metastatic cyst. Back then, I also started Tagrisso which I'm still on.

Four years later I had a small recurrence in that area which was stopped by one more round of radiation. Unfortunately that last round led to necrosis which has caused drop foot on the right side because all of this is above the left parietal lobe.

I wish I had more positive news, but brain tissue is rather soft. As I understand it, the radiation has caused this delayed reaction because it also destroyed blood vessels, glial cells, and other brain matter that leads to a downward cascade. You didn't say where in the CNS you're concern lies. I imagine the spine won't have these issues due to the lack of widespread soft tissue.

You might want to check with MD Anderson as they have some of the leading oncologists in EGFR+ mutations. I wish you all the best!