Hey my friend! Okay, I asked some of the same questions from my endo and the nuc med department at my hospital (in hopes that next time my scan is I-123 *not* I-131).
The I-123 is usually out of the body within 48 hours so after the scan (and they scan the entire body) they can give you the treatment dose of I-131 within just a few days.
If the cancer cells absorb iodine, they will absorb the I-123 (and I-131). If nothing shows up (and usually after the RAI anyway) you should have a PET scan. However, with your history a PET scan would still be recommended (talk to your doctor).
The shortness of breath could be from your increasing TSH - sometimes when the TSH climbs it brings depression and anxiety attacks and the shortness of breath could be anxiety.
Keep us posted! And, on a personal note, since I'm not on the forum a lot lately, send me a PM and let me know how things are!
Huge hugs
Utah
Have no idea on the subject but GOOD LUCK! hope it all turns out fine:
Jen XxX