How do you treat inoperable T1-2N0 apical lung cancers near the brachial plexus but without extension outside the lung?

This is a challenging question, and there are certainly a range of reasonable answers.

I would agree with @Dr. First Last that the Forquer/Timmerman paper establishes there is significant risk of plexopathy when exceeding 24-26 Gy in 3 fractions. On the other hand SBRT offers superior local control ...

To update these excellent answers from 2018, there have been several helpful manuscripts on the topic of radiation-induced brachial plexopathy (RIBP) following SBRT that have been published in the past year.

Morse et al., PMID 34929402: 5 of 78 (6.4%) patients developed RIBP, 4 of whom received 50 Gy...

With 3-4 fractions, Timmerman found that patients with a maximal dose of 26 Gy or less had a fairly low risk of BP (8% vs 46% for doses higher than 26 Gy; the original 3 fx protocol recommends 24 Gy/3 fx). The NCCN constraint is 32 Gy for 5 fractions. Another series with 75 patients with apical tumo...

I am making an assumption that normal tissue tolerance cannot be achieved with a 3-5 fraction regimen of SBRT for the brachial plexus from the question you have written.

In that circumstance:

I have utilized a regimen from a peer-reviewed published article by Yung T et al. "Outcomes of accelerated hyp...