Here is the channel of a guy who had brain cancer and he says that keto helped him a lot and now is cancer free:
https://www.youtube.com/channel/UCoQ...RT8w6uqDmq12Hg
Also, you should watch Dr. Eric Berg's videos they are all about keto and he even has some videos about what cancer patients should eat! Basically, he says they should be eating only organic keto foods! here is his channel:
https://www.youtube.com/user/drericberg123
All the best to your brother I hope he will get well very soon!