PET scans are not very effective scans for the two most prevalent types of thyroid cancer (papillary and follicular). They just don't detect the small size of the cancers well.
Thyroid tissue absorbs iodine much more effectively than the glucose-based radiation that a PET scan uses. Your followup scans should be I-123 or (less desirable) I-131 scans and if a recurrence is detected a large "treatment" dose of I-131. Based on your thyroglobulin numbers you need to talk to your endo about another "treatment" dose of I-131.
I just had a negative PET scan result after a TT last February and RAI in June. My thyroglobulin levels 2 weeks ago were 4.9 and last week they were 6.6 and we just took them again with Thyrogin injections so we'll see what the actual numbers are next week. Did you have a positive PET scan or did your endo just diagnose your recurrence because of the rise in your thyroglobulin? What was your course of treatment? Thanks so much in advance for your thoughts!
According to my endo (who specializes in thyroid disorders), it's not the number but the trend in the numbers on the thyroglobulin that are worrisome - as long as everything stays below "7". My recurrence was found from my thyroglobulin going from 1.7 to 2.1 to 3.9 to 5.2 over the course of about 8 months and -- sure enough -- I had a cancer recurrence. It's all in watching the trend. I always show "positive" at a level of around 2 now and we just watch to make sure that there is no increase in the trend.