There is a lot of practice variability with ultra-central stage I inoperable lung cancers around the country/world. Some providers prioritize "doing no harm" and prescribe more conservative dosing schemes (2.5 to 4 Gy fractions). Undoubtedly, there is a lower risk of complications with this approach...

The data from the AAPM working group High dose per fraction, Hypofractionated Treatment Effects in the Clinic aka "HyTEC" essentially the QUANTEC of Radiosurgery and SBRT provides important insights on the TCP and NTCP of Radiosurgery. This COMPENDIUM published in the Int J Radiat Oncol Biol Phys of...

Perhaps the most robust data are from RTOG 0813 that showed 12 Gy x 5 was safe and highly effective while 11.5 Gy x 5 was probably just as effective. I hope those authors will comment on this question. @Andrea Bezjak et al. PMID 30943123