I had a basal cell carcinoma which I've had very good results with using damp baking soda on massaged directly onto the site. I wonder whether swishing and gargling with a spoonfull of baking soda regularly would help your dad. There is alot of support for baking soda as an anti cancer protocol and you can check it out here if you're interested:
Many believe that chemo is the worst thing you can do in terms of it actually depressing the immune system even further than it already is. I'm sure your dad would instead benefit from immune enhancing foods and supplments such as high doses of Vit C, D, echinecha, fresh vegetables and a good multi vitamin and mineral supplement along with Iodine and selenium.