First off, great story and congratulations at being a fighter.
I have two ideas, the first would be to do a portrait style picture of a medical symbol with the words retired somewhere on it. Medical symbols I'm thinking of are like Da Vinci's human body, or the medical cross with the wings and snakes wrapped around it.
My other idea would be to ask for a piece to be made from members like "Intarsia92" "Charles Dearing', etc., and pay them for the piece. I don't think it lessens the specialness of the gift if you don't actually make it.
Hope this helps, and good luck with the project.