I'll preface this post with cancer is not to be taken lightly and by self evaluation.
I am not a doc, so I will not say that any treatment vs another is better or a path even worth pursuing.
I have seen a movie, (which in an of itself means very little) that talked about curing cancer with diet. In it they were highlighting the Gerson Treatment. A brief search online will show both, it is a hoax, and it is a miracle cure, so it really boils down to what you believe after weighing your options. http://gerson.org/gerpress/
I would say if it were my loved one, I would research all options, and together choose the one that we can all live with the possible outcomes. I had a friend in my platoon who had a very nasty form of cancer, and was not given much time. He pulled through, using traditional medical tech. of radiation. He lost his hair, weight, desire to live sometimes. He was not able to eat fresh foods, because with radiation to the level he had been given, any bacteria would have made him very ill. He wasn't able to fly or do his job during treatment. Now he is in remission, and is fine. But it was a long painful process.
I know your original post was asking if a MCD retreat would be a good option, but I cannot answer that, I haven't ever been to one, and do not in any way feel competent to answer that question.
I think everyone here wishes you both the best of luck, and strength to push through.