Steve,
Wow, so glad to read about your Dad. He's a wonder! Is he swimming again, yet?
I can't give advice, but here's what I did. After my esophagectomy for stage 1 EC in 2005, I had a consultation with an oncologist. Tests had shown no spreading of my cancer, but he advised I do Chemo just to be sure. Since he was on the fence and couldn't be sure it would even do any good if something had spread, I said no to the chemo. I was having a hard enough time as it was. I have not regretted that decision. I've had clean Pet scans since.
Good luck with whatever you and your Dad decide.
KEEP MOVING,
Steve