PET scans simply measure sugar intake and give many false positives for cancer with an exceptionally high error rate for tongue cancer. CT scans are fine for initial identification of cancer and in fact it was a CT scan that first identified my base of tongue cancer.
CT scans are so reliable that even if a CCC orders a PET scan, they almost always combine it with a CT scan.
I know from personal experience just how horrible it is when a PET scan goes wrong and indicates Cancer when it's just sugar intake from healing tissues. Perhaps your son's doctors have had similar experiences so are being cautious.
Charm