@curiouskitty, I have experience with both radiation to the brain and subsequent radiation necrosis. I was first diagnosed with the EGFR Exon 19 mutation in my right upper lung lobe in 2018. I had a lobectomy followed by 33 rounds of chest radiation and four rounds of carboplatin and pemetrexed (because the cancer had spread to a nearby lymph node.)

Two years later, the cancer came back as a 3.2cm diameter cyst in my left parietal lobe. I have it surgically removed followed by four rounds of radiation. It took a while but I recovered all of my ability to move.

Four years later I had renewed activity in that same area, so I received one more round of targeted radiation. Eight months after that I developed radiation induced necrosis in late 2024. We successfully treated that with Avastin, By then I had developed drop foot on my right side and was somewhat limited with the use of my right shoulder. MD Anderson and my local team have been fighting radiation induced necrosis and new tumors in that area ever since. My second brain surgery last January has left me with serious right side physical challenges. For example I'm "typing" this with voice to text. I'm returning to MD Anderson for an ABTI MRI on Monday. (Advanced brain tumor imaging)

So it took five rounds of targeted radiation before I developed radiation induced necrosis. I was on 80mg Tagrisso for those four years after the first brain surgery. Now, after almost six years, it's still considered limited resistance because there is no trace of cancer anywhere else in my body and no new mutation. You should be fine with just one round of limited radiation. I had no immediate side effects from the radiation. Best of luck to you and yours in your journey!