I'm so sorry your brother died so young, durhamjen. They mustn't have caught it in time.
My brother got a brain tumour too - at age 70. It was called a glyoma. It was terrifying for all of us, but in his case they caught it on time, as it manifested itself early through seizures. He had a year of chemo, spaced out every so many days.
As soon as he got it he discussed it with the family: his son is a respected medical researcher who runs a Mayo clinic lab in San Diego, our BiL a physicist, our sister has done extensive research on nutrition, and he decided on the ketogenic diet: lots of oily fish and fatty food, lots of greens, dairy, eggs, but no grain, no sugar and few carbs.
Anyway, it is now two years later and he's in remission. His Doc is surprised and pleased, and is considering the benefits of his diet for his other patients.
So much that goes wrong can be blamed on the food we eat. I'm not saying I've got it right - people have been eating grain for thousands of years, but for my family, giving up grain, giving up sugar and sugary foods, and eating as much natural fat as we want, is working.
My husband thinks I'm insane, and eats lots of wholegrain bread, loves his mashed spuds, and eats as much baked stuff as he can get away with in view of his diabetes. He has type 2 diabetes, diagnosed at age 70, painful hands and feet, insomnia, depression, panic attacks and other conditions.
But I'm wrong and he's right.