I would also look into oxygen therapies (hyperbaric) and I would not consume Sugar of any kind (refined, fruits, grains...) Remember Sugar feeds cancer. I know he is just a little boy and doing without something sweet can be tough. Healthy organic berries such as blueberries, raspberries, gogi berries would be good for him.
On one of our trips to the Bio Medical Center, located in Mexico, one of the doctors there stated that he use to work in a children's cancer hospital out east. He said that he could no longer support the work they were doing, because he saw first hand that the children were dieing from the treatment they were receiving long before the cancer would have taken their lives.