I agree with the wisdom of Eileen. Of course in my case, the professionals let me down by not doing that pre-treatment baseline test. My doc is happy with any reasonable number as long as I feel ok. Another issue is that the dose we get cannot be a perfect match to our individual requirements because of the steps between available dose strengths. I know for me the prescribed dose is just slightly higher than I need because if I take it on schedule (one per day) after several weeks, I will develop heart rhythm issues (a common symptom of too high dose). Fortunately, due to human nature I seem to forget to take my dose just often enough to stay at the right dose overall for me.

Everyone that has been through H&N radiation should become familiar with the symptoms of thyroid imbalance. It is extremely common for to have post treatment thyroid problems.