When do you recommend RT versus stenting for SVC syndrome in patients who cannot receive systemic therapy?

The option to stent upfront should always be considered before starting palliative treatment for SVC syndrome. Especially since it can offer reliable relief in a more timely manner. More importantly, it can at times avoid premature death in those in whom XRT might not work.

However, it's critical to...

I agree with @Dr. First Last. I've always tried to get stents put in for those patients if IR thinks it's feasible to do so safely. Otherwise, proceed with rads.