At the very least, a radiologist should read the xrays.
It's obvious to me, that your vet isn't up to date with treatment. There are many who last over the average of 14 months if the amp is done before lung mets and you also do chemo.
I understand about not doing an amp (I have lost two to osteo and I did not amputate). However, properly medicating is imperative (or however you spell that).
How old is he? (the grey, not the vet ) edited: I see 11. That is not too old. Depends on the kind of tumor and where it is exactly and the lungs.