My late mother refused to allow me to go with her to appointments. I'm still not sure why. I accompany hospice clients as a volunteer and take notes. I counsel all of my clients to take someone with them. Same with my spouse. Once, he misheard test results and it caused us much worry, as I was not there. He has hearing issues. I can empathise!
My dad tolerated radiation well, as did mom. But it didn't 'cure' them.
Dad ended up with delirium, due to an infection, which went undiagnosed in the ER. We suffered with this for weeks until his GP phoned. This is the kind of thing you need ask an oncologist: what side effects, e.g., infection, can you expect. Delirium is treatable, dementia, which masks it, is not. He had both.