I'm so sorry for you Richard1966, it's an awful situation to be in (as I have) and I know you just want what's best for your dog without him suffering. I'm certain I would do as you and give him every possible chance, but if it looked like it wasn't working, then the inevitable will have to happen. I think by letting the dog have treatment, you know then you gave him the best possible chance and it will be more of a comfort to you later, than if you had him put down straight away, you will always think 'what if etc'. This is just my opinion - I hope it helps in some way, and I wish you all the best.