PET Scan imaging - false positives?

My Dad has recently had a total thyroidectomy for a 9cm x 4cm goiter -- Left side pathology revealed papillary cancer with follicular variant with vascular involvement. Cervical lymph nodes were negative. The tumor has also been labeled poorly differentiated. He had a PET scan done in Jan. that showed uptake in the lungs and at the thyroid site. This cancer is not iodine receptive so he has not received I131....He was denied enrollment in a clinical trial for biomolecular therapy because of a bundle branch problem with his heart. The drs. have him on 150mg thyroxine daily and have scheduled him for a CT scan on March 10, 08 to see if the tumors have grown....Right now we are all scared and he is definitely angry because he feels like he is not being offered anything proactive. I do not believe the results of the PET -- I have read of false positives and he has a history of tuberculosis scarring and has been treated for bronchitis since a week before the thyroidectomy. I think the dr. may be thinking that this is an 84 year old man in reasonably good health sans thyroid cancer, and chemo/radiation would really compromise his day to day function, but I also understand his frustration at feeling like he is not being proactive when the cancer is poorly diff. Please Help!!!! We need some advice. Should we get a second opinion? Should we insist on a biopsy of these so called lung lesions in order to know what we are dealing with? i would very much appreciate any info. anyone can share....Thank you!!!