Depending on his bone structure and muscle mass, 220 might be a bit heavy for a 6'1 man. I am 6'2 and weighed ~185 before my cacner surgery. I weighed 160 after leaving hte hospital, and for 3 years, I have been 172 with very little fluctuation. If he is eating well and has excess body fat, he will lose it. This is not a problem. What matters is his overall health and strength.
Don't just take any whey protien. I needs to be cold processed, not cheese by-product (as most are), and it needs to come from hormone-free milk. Immunopro is the best and most affordable that I have found. Take it first thing in the the am. I take it 15 minutes before I have my morning juice and vitamins.
Also, you need high-trypsin enzymes between meals. I use Omnizyme Forte. Again, I stress the importance of some good reference material. You do not want to setup your nutrition program ad-hoc, based on anonymous internet posting. The Kelly/Gonzales protocol or the HealthQuarters protocol ("A Cancer Battle Plan"), are my recomendations, along with a Moss Report for your Dad's particular cancer.