Hi, Audrey
I didn't find any studies comparing the large 2 to 3 cisplatin doses (like DavidCPA, I am assuming this is your father's protocol), but I did find a comparison of the lower dose, weekly option and it indicates that total dosage doses make a difference:

http://www.headandneckoncology.org/content/1/1/17/

This is a small, single institution study, so take the numbers with a grain of salt - but they do indicate a better result with the full dosage.

Your father's doctors should be carefully monitoring his bloodwork to determine if it safe for him to continue the treatment. It is dreadful to watch a loved one go thru this, but sticking to the protocol (both chemo and radiation) as closely as possible will give him the best chance of a cure.
Maria