Hi Suz, in addition to standard treatments, there are additional things that you can do to help in terms of diet, fitness etc. A couple of good books on this topics are:
1)Surviving Terminal Cancer: Clinical Trials, Drug Cocktails, and Other Treatments Your Oncologist Won't Tell You AboutbyBen Williams(Jul 1, 2002)
2)
Anticancer, A New Way of Life, New Edition[Hardcover]
David Servan-Schreiber MD PhD(Author)
3)Foods to Fight Cancer: Essential foods to help prevent cancer[Paperback]
Richard Beliveau(Author)
The first one was written by a GBM survivor and is a very good book - though your son's situation is not as serious. The last two discuss specific diets that can help cancer. Also, curcumin (turmeric) has been shown to have good anticancer properties.
Good luck. I believe your son has a very good chance of beating this.