Anyone ever had or heard of this ?

         So we meant with the radiation oncologist and got my dad's newest pet scan results and there confusing as always. There is still something highly sususpicious for cancer in his pelvis but the confusing part is that the FDG Uptake has went down since last pet scan and the " mass" isn't getting any bigger . Anyone else ever had FDG uptake go down but it still turns out to be cancer ? This is confusing to us and important since they not want to do more radiation and chemo which they say the radiation could injury my dad's bowels . So my dad won't let them do nothing until they know for sure it's cancer so another CT scan in 2 months . 

          Side note the pet scan also had FDG uptake increase at the base of my dad's tongue with tissue thicking there as well of uncertain malignant potential and low level uptake in a nodule at the thyroid gland right lobe/isthmus . My dad's thyroid was removed long ago does anyone know what this could mean ? The radiation oncologist didn't even mention this I read it online . 

       Hopefully someone can help me out on this my dad is sooo happy and see's all this as meaning he could be cancer free. I would never burst his bubble but to me there is still concerning thingst in this pet scan like does my dad have tongue cancer ? Could he still have cancer and FDG Uptake go down ? Hopefully yall can help me out as always thank you so much .