Kiba and Nancy, and all, we have had some discussions about hypothyroid before. By using the "search" word (that is too small) I found several including this OCF page:

thyroid

Any of us that have had radiation treatments to the neck have a significant chance of thyroid output problems, usually low output or hypothyroid. The thyroid produces hormones that control nearly every function of the body. Essentially metabolism slows down with hypOthyroid and speeds up with hypErthyroid. The normal range of TSH (Thyroid Stimulating Hormone) is .3(note decimal point) to 5, Higher numbers indicate hypothyroid, lower numbers indicate hyperthyroid. When I had 8 out of twelve symptomes and finally went in to get tested I was at 18. I can tell you that thinking and memory were definately affected, as were body temperature (mine still runs 96-97 deg.), fatigue, heart and lung function, and an inability to get out of bed in the morning. In general if it gets low enough you feel really crappy.

After getting on synthetic thyroid hormone pills, things got better-until the numbers began to creep up again. My first dose was 50 Mcg (not Mg) now I am at 132Mcg after 1 year. It seems that my thyroid is gradually shutting down. No one knows when it will settle down. It has been 3 months at 132Mcg and I can tell it ain't right anymore.

Brian's note about the symptoms being similar to a host of other alements is correct, however body temperature is a simple at home test that is quite accurate. Simply take your body temp. before getting out of bed in the morning. If you are less than 98 degrees consistantly for a week or more, you need to get tested for hypothyroid. Especially if you have some of the other symptoms. Left untreated you will become less and less functional, and it can become serious.

The test is a simple blood test.

I strongly advise getting tested BEFORE you begin radiation treatments. This will provide a "normal" baseline should you develop problems later.