I am glad that you have him on the Budwig Diet but the Chemo/Radiation will Destroy him as it is... If he's set on being seen by a Dr. I would head to Mexico and use the Sono/Photdynamic Therapy which will cause no toxicity.... A clinic that does this is http://www.cancer4hope.com
and there's is another clinic in Mexico across the boarder of Texas and less costly but not as nice but works. The other clinics in Mexico which don't have this therapy is BioCare Hospital and Gerson Chipsa Hospital... BioCare has a outpatient treatment for about $2500 developed by a Greek Doctor.
If he sent on Chemo they can use insulin chemo where you use small amounts of the drug but way more effective... Another Option is the Oleander Plant which is a toxic poison and you could think of it as a chemo drug but in smaller doses have less side effects.
Yes its your dads choice and some will only look for guidance from a Doctor so maybe show him these other choices in Mexico.... I don't know your fathers type of cancer but the Sono/photodynamic looks like the best option with good success.