Would you recommend getting a PET scan or an iodine whole body scan in a patient with recurrence of thyroid cancer in the neck previously treated with total thyroidectomy and 2 radioactive iodine ablations in the past?  

The usual patient who has had 2 doses of I131 is not usually iodine-avid or iodine-sensitive. You will be able to determine with this information: When were the 2 doses of I-131? What did the post-therapy scan show after the last dose of I-131 and Was the tumor responsive either by Tg or tumor ...

It depends on the pathology of the thyroid cancer. If poorly differentiated or oncocytic (which often doesn't respond well to RAI), I would do a PET. Also, the timing of the last RAI treatment would affect that decision. If just within the past 1-2 years with a negative post-treatment scan, I think ...