How do you construct your target volumes for superior sulcus tumors?

This is one of my favorite topics, so I apologize in advance for my verbosity.

1. Tumors invade: I worry that our RT fields, in general, are getting too tight (i.e., cancer often invades beyond what we can see on our imaging, and our CTV margins are often small). This is especially true for Pancoast tumors that tend to invade into the soft tissues of the supra-clavicular area (e.g. posteriorly and superiorly to the imaging-defined GTV). For example, I have certainly seen patients with neurologic symptoms in the arm, but no MRI evidence of tumor invasion of the plexus (even when clinically there clearly is ‘involvement’).
2. The margins of a tumor are hard to detect on PET or CT. Plus, image fusion is not perfect.
3. CTV margins that we routinely a...

These are typically tri-modality cases and I usually stop at 45-50 Gy, but if treating definitively.

I would simulate with 4D and contour a GTV-ITV and add 0.5 cm CTV expansion, carving out of uninvolved bone/muscle. Then, I'd add 0.5 cm PTV expansion.

Unless it is T4 and invading vertebra, I have not seen any issue with the spinal cord, but in that case, would have to limit to max dose of 0.3 cc getting 50 Gy, which may underdose part of the tumor. You can exceed it, if they are definitely not getting surgery and the patient understands the risk of badness, but I would hesitate to go much higher.

As far as the brachial plexus, I would accept higher than 60 Gy if it is adjacent/within PTV. Many of the RTOG trials accept up to 66 Gy. I thi...