What is the case for or against using protons for lung SBRT?

Proton therapy is a tool in the radiation toolbox to use when needing to take advantage of avoiding normal tissue. For the vast majority of cases, proton therapy is not needed for lung SBRT and of course, there are concerns about motion, low density targets, under coverage, and beam overshoot. But.....

To answer the question first: My general opinion is that there are not a lot of reasons to do it, currently.

Keep in mind that there are some wide differences in technology available at different proton centers: some do not have CBCT image guidance, 4D-CBCT is not available, differing spot sizes, av...