Have we established standard doses for radiation therapy for H&N cancers?

You've asked a *really* wide-ranging, thought-provoking question. That said, if by 70 Gy you mean 35 fractions of 2 Gy apiece over 7 weeks as *the* "optimal dose," I can think of a few references off the top of my head where that's not optimal per se. Dosing also entails the timing/frequency of dose...