The 3 mega dose have been used for a longer time.... so there is more data on it.
If you have any data that directly compare 7 vs 3 applications for H&N cancer together with radiation, then I would be interested to know where that is. The only clinical trial that I found was the European and US studies published in 2004 that used 3x cisplatin in conjunction with radiation.

In many cases the 3 dose option is now not on the table at all, regardless how old and fit you are. Form a pharamacokinetic point of view, especially if you consider the synergism with the daily radiation, the 7 doses make a hell of a lot more sense.

M