Tissue regowth after thyroidectomy and RAI

Hi all. I had a thyroidectomy and two rounds of RAI in 2002. All has been fine since. Yesterday I had my routine neck ultrasound and my endo was shocked- tissue has bilaterally grown back. My thyroglobulin level is fine ( less than .5 is what I think it always says on my bloodwork). My TSH is 0.3. My endo (who is also the nuclear medicine doctor who administered my RAI) said, based on the ultrasound, other than there being tissue regrowth, it doesn't look like cancer. Nonetheless he is sending me for a bilateral ultrasound guided biopsy next week. I am freaking out. I am looking for people who have had this type of thing occur and it NOT being cancer. I'm scaring myself silly over this!! Thank you!