I am post head and neck surgery and radiation for SCC of my upper jaw and palate. My CT shows Otomastoid opacification on that side. How is that treat?

Depends on cause. We have to know your symptoms & look at the CT scan (often examine ears as well) to come to a diagnosis. You've described the CT appearance (darkened mastoid cells) but the CAUSE was not mentioned. Is it an infection? Treat it with antibiotics. Is it from an allergic reaction? Treat with antihistamines. Is it from radiation? Hyperbaric oxygen is only known treatment for late effects of radiation.