Hi you may want to post this in the Head and neck cancer group that you have been posting in as they will be able to help you based on their lived experience.
But the best people to talk with are your dad's clinical team as they are best placed to look at the best support for him. I have a totally different cancer so Acid Reflux was part of life.... but I was prescribed medication as well as antacid like Peptack......one thing that helped me was raising the head of my bed by putting some timer under the bed legs...... I could not sleep with extra pillows but the slight raise in the bed did help me.
