@sakota One big concern about possible spine surgery is that for fusions, bones need to be able to heal and fuse, and if any artificial device is implanted, it depends on bone quality to work. Implanted artificial discs and spine hardware are screwed into bone. Bone is a living tissue and is actively reabsorbed and replaced by cells called osteoblasts and osteoclasts in a life long process. I was looking for literature that would relate the effects of radiation on bone quality, and I found this that may be of interest.
https://pubs.rsna.org/doi/abs/10.1148/59.5.744
Surely this is a question for your doctors, but what I'm reading is that radiation affects bone quality and health and that cancer radiation treatments can play a big part. Since you know that you have scheduled future radiation in 5 months, that could very much affect if spine surgery could be successful in your case, but your specialists will need to answer that question. It must be hard to be in this place not knowing what the best choices would be. The other thing that came to my mind was about the type of radiation you will be doing. At Mayo, they have a Proton Beam that is very targeted radiation. It might be worth checking to see if that would be a safer radiation treatment that would have less effect on your spine and bone health. Here is some information on the Proton Beam. This is new and not a lot of facilities have this technology at this time. I don't know if this would change the treatment options for spinal stenosis in your case, but you certainly can ask.
https://www.mayoclinic.org/departments-centers/proton-beam-therapy-program/home/orc-20185488

i had Vertiflex 10 days-ago. still in pain. spacer put in L4 and L5…
hope i’ll heal and pain will go away