Sounds right to me. Husband had pet when first diagnosed, showed nothing, had one more in between chemo and radiation, showed nothing, then had one about 6 weeks after finishing treatment. Stage 3 SCC, unknown primary, 1 right lymph node removed. Last pet left sternum lit up, follow up mri showed a little somthing, dr ordered biopsy IT WAS NOTHING!!! I thank god for all the drs involved to be cautious...but damn we were scared.