Early scans are often inconclusive and reading radiologists tend to be very conservative. The post Tx biopsy is a little unusual but so is cancer of the hard palate (we see many more tonsil and tongue cancers here).

A PET scan this early will probably yield some false positives as well, as the healing process mimics the same increased sugar uptake as cancer does.

PET/CT is the best and most accurate form of PET - here is a link to a reasonably non technical discussion - for you non-believers (we have had many animated discussions on PET scans here) go to the GE links (image gallery) on the site and check out the patient studies.

Is he being treated at a CCC like Stanford or UCSF? I live 15 minutes down the road from you so feel free to ask for my phone number through the personal email feature on the forum. I will be happy to talk with you personally.