Ski
I had RAI twice (please do not panic ~ I was an unusual case). The first time my endocrinologist did not have a discussion with the radiation/oncologist who formulated my dose. We had agreed that I wanted an ablative dose (I wanted to start from zero), and the dosing doctor had the feeling he could give me "just enough," so he gave me 10 millicuries. It was not enough. The second time I was given 22 millicuries.
Let me put this into perspective, and give you some of the mechanics of the RAI as well.
First, when you have a scan, the result is a percentage of the iodine that is taken up into the thyroid. When we are sickest, our thyroid takes up a LARGE percentage of iodine. So, at an 80% uptake, my initial effective dose was 8 millicuries (80% of the 10 millicuries in the dose). After one RAI, my thyroid was affected and had a much lower uptake ~ 25%, I think ~ so for the second RAI, I took 22 millicuries but only retained 5.5 millicuries in my thyroid.
Here’s what happens. We take the RAI, and most of it goes to our thyroid (thankfully, the only place in the body that iodine is taken in). It begins destroying thyroid cells. It does most of its work in 6 weeks, but can continue to destroy cells for up to six months.
The RAI that is NOT taken up into our thyroid leaves our body by fluid waste channels (mostly urine, also a tiny bit in sweat and saliva). Any of this "cast off" RAI ingested by another person would go to their thyroids and cause damage. Not much, but why risk it? As a result, we keep to ourselves for at least the first couple of days, as that "cast off" RAI is leaving our body. After 48 hours, that’s done. We are advised to drink LOTS of water and make sure we visit the toilet every hour or so, to limit any exposure within our bodies and flush out the excess ASAP.
Remember please that thyroid cancer patients can receive up to TWENTY TIMES the doses we get (yes, hundreds of millicuries), and even that dose of RAI is considered safe in the long term.
The dosing calculation is part art, part science. It is derived from your level of hyperthyroidism, your uptake, and other details. It is NOT an absolute. You may want to ensure that your endocrinologist and radiologist/oncologist have a discussion and AGREE upon the dose you need, it will probably eliminate at least a little of the uncertainty.