Mickey

It's a good sign that you caught your BOT tumor so early. The majority of BOT tumors are T3 by the time they are DX. You have gotten great advice in the prior posts which I will not repeat.
I do urge you to get a blood test right now to get your exact thyroid hormone level number before starting radiation. Even though the classic textbooks recommend it, for some reasons many clinics do not do it, instead they rely upon post radiation blood work. That approach is worthless since the so called normal range of TSH levels is so large as to be meaningless. Simply put, you will want your TSH levels to be the same as they were before and there is no way to ensure that if you do not know what your current TSH level is.
I was fortunate to have my exact number (in the low 1s) since the "normal range" can be up to 5 according to the labs. (Although most endocrinologists who went to medical school in the 21st century agree that 3 is the maximum - the labs and older doctors use the 20th century values)
Misdiagnosed thryoid hormone deficiency is one of the major causes of lingering post radiation fatigue.
Keep the Faith
Charm