Yep, I needed to have RAI twice ~ the first time I just wasn’t given enough, and I never went properly hypothyroid (my TSH remained suppressed for more than a year ~ can’t say I didn’t try!!). I tried to convince myself that I wasn’t really sick any more, but once I had the second treatment and went truly hypo, I could see I’d still been ill before it was done. There’s a good reason to have a goal of being within the normal range in both measurements (T4 and TSH).
The only odd thing about the second RAI is that you usually need a higher dose in order to get enough of it remaining in the thyroid to finally do the job. It’s really just mathematical at that point ~ say that your initial uptake percentage (before any treatment) was 80%. Say that you were given 10 millicuries as an initial treatment dose. 80% of that dose would have ended up in your thyroid (8 millicuries) after the first 48 hours. Once you’ve had one dose of RAI, it should have destroyed some of your thyroid, so your uptake percentage prior to the second dose will be far lower. I think mine was somewhere around 45% before the second dose. Since the uptake percentage tells you exactly what percentage of your initial dose will stay in the thyroid, you need to take more the second time to end up with the same "active" dose inside your thyroid, to make sure the job gets done this time. The only difference then is the amount of RAI that is being flushed out of your system in the first 48 hours.
I wish you luck!
