Can your thyroid return to normal after radiation treatment?

No: If it is radiation to the thyroid, it never becomes normal and need to have life long thyroid supplementation.

YES: However, that's not usually the desired result. Hyperthyroid patients who receive radioiodine treatment are best off if the gland stops working for a couple of reasons: 1) grave's disease could relapse. 2) exposure to radioactive iodine increases your risk for later developing thyroid cancer as long as your gland is active.