Hi Chris -
I'm really sorry that your dad has to go through this. This is a wonderful forum....everyone here will answer any question you may have, and they helped me tremendously when my husband was ill.
My husband had a PEG tube inserted prior to beginning treatment, and it was a godsend while he was going through his treatments. For a while, he was eating somewhat normally, but would supplement with a liquid nutrition called Jevity, prescribed by his oncologist. It provided him with fluids, fiber, calories, fats, and vitamins & minerals, and comes in different calorie levels. After beginnning radiation, he eventually had a terrible time eating, drinking, or swallowing pills, so the Jevity became more important. When he could no longer swallow medications, most could be crushed and flushed down the tube with water. It was very easy to keep him hydrated also, which is very important when going through chemotherapy or taking large amounts of painkillers.
All the best to you and your dad!
Judy