For this trial, the rationale is more than immunogenicity of course, although it would be nice if some magic happened. The more prosaic motivation is to see if one can safely improve local control and thus maybe pFS and OS by judiciously dose escalating with a highly conformal and upfront boost.
This is a lot different than escalating all disease from 60-74 Gy...not exciting, but different.
Agree about the sequencing question though, and all these arguments come out with every negative concurrent XRT/IO trial.
I'm convinced that radiation induced immunogenicity is a high variance problem in people. (Much less so in nude mice...why we have baller pre-clinical data.) In fact, I'm convinced that prior to the advent of targeted IO to conserved proteins like PD-L1, the high variance problem was why IO had been such a flop over 30 years of clinical research, despite clear evidence of periodic complete responses in patients.