My oldest sister had brain cancer, and radiation and chemotherapy helped save her life
What makes you so sure it was radiation and chemo that saved her? Plenty of people think Gerson therapy saved their lives. Others swear by prayer.
My dad did chemo and radiation. He's dead. He would have died anyways, of course, but the quacks he put his trust in ensured that his last months on this earth were as agonizing as possible. But hey, it worked out well for them financially.
My uncle took the same route in addition to a strict vegetarian diet, but he didn't even last as long as my dad.
My mom's friend also decided to trust her doctors. Guess what happened to her...
Given the success rate of chemo and radiation I would rather take my chances with the Gerson therapy. Juicing and dieting may not extend your life, but at least it doesn't make your hair fall out or force you to drink stuff that tastes like vomit to survive. But hey, it's your life.