James,

Typically, Radiation Pneumonitis is considered a subacute radiation injury. It usually has symptoms that mimic bronchitis and usually resolves with supportive care. The role of HBO in subacute radiation injury has not been well established and the UHMS Indications Manual (15th ed) makes note of this on page 168-169.

That being said, if your patient has a diagnosis of radiation penumonitis,  (preferrably tissue biopsy proven), and the patient is more that 6 months out since his last dose of radiation, then you could make the case that this is STRN of the lung. However, patients with radiation pneumonitis may develop pulmonary fibrosis. There have also been no controlled human studies to evaluate various treatment options for radiation pneumonitis (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8097634/).  Therefor, given the lack of evidence, I would be reticent to offer HBO at this point.