Unfortunately, I do not know anything about this type of brain cancer or how radiation in that area of the brain will affect a 15 year old. I did look it up on the internet after reading your post & found a lot of information about it. One website was called something like "save our dylan". The son was diagnosed at 18 months and is still doing well about 6 or 8 years later. I can't remember for sure. The family has been posting everything they have done since he was first diagnosed. Maybe you will find it helpful. My best wishes and prayers to you, your daughter, and the rest of your family.
Jackiekay