 of patients remaining euthyroid at 10 years after therapy, in comparison to other treatment protocols. Glinoer and Verelst also report successful use of this strategy [59.1]. As noted, antithyroid drugs may be given starting 7-10 days after RAI without significantly lowering the radiation dose delivered to the gland.
Treatment using 125-I was tried as an alternative to 131-I, because it might offer certain advantages . 125-I is primarily a gamma ray emitter, but secondary low-energy electrons are produced that penetrate only a few microns, in contrast to the high-energy beta rays of 131-I. Thus, it might theoretically be possible to treat the cytoplasm of the thyroid cell with relatively little damage to the nucleus. Appropriate calculations indicated that the radiation dose to the nucleus could be perhaps one-third that to the cytoplasm, whereas this difference would not exist for 131-I. Extensive therapeutic trials have nonetheless failed to disclose any advantage thus far for 125I. Larger doses — 10-20 mCi — are required, increasing whole body radiation considerably [ 61, 62].
SAFETY PRECAUTIONS AFTER 131-I THERAPY
Doses of 131-I up to 33 mCi can be given to an outpatient basis, and this level is rarely exceeded in treatment of Graves’ disease. However patients must be given advice (written if possible) on precautions to be followed to prevent unneccessary or excessive exposure of other individuals to radiaactivity administered to the patient. For maximum safety, patients who have received 20 mCi should avoid extended time in public places for 1 day, maximize distance (6 feet) from children and pregnant women for 2 days, may return to work after 1 day, sleep in a separate (6-feet separation) bed from adults for 8 days, sleep in a separate bed from pregnant partners, infant, or child for 20 days, and avoid contact with body fluids (saliva, urine) for at least one week. Lower therapeutic doses require proportionally more moderate precautions.This topic is well covered in an article by Sisson et al (http://www.ncbi.nlm.nih.gov/pubmed/21417738).)
Course After Treatment– If adequate treatment has been given, the T4 level falls progressively, beginning in one to three weeks.. Labeled thyroid hormones, iodotyrosines, and iodoproteins appear in the circulation . TG is released, starting immediately after therapy. Another iodoprotein, which seems to be an iodinated albumin, is also found in plasma. This compound is similar or identical to a quantitatively insignificant secretion product of the normal gland. It comprises up to 15% or more of the circulating serum 131-I in thyrotoxic patients . It is heavily labeled after 131-I therapy, and its proportional secretion is probably increased by the radiation. Iodotyrosine present in the serum may represent leakage from the thyroid gland, or may be derived from peripheral metabolism of TG or iodoalbumin released from the thyroid.
The return to the euthyroid state usually requires at least two months, and often the declining function of the gland proceeds gradually over six months to a year. For this reason, it is logical to avoid retreating a patient before six months have elapsed unless there is no evidence of control of the disease. While awaiting the response to131-I the symptoms may be controlled by propranolol, antithyroid drugs, or iodide. Hypothyroidism develops transiently in 10 – 20% of patients, but thyroid function returns to normal in most of these patients in a period ranging from three to six months. These patients rarely become toxic again. Others develop permanent hypothyroidism and require replacement therapy.
It is advantageous to give the thyroid adequate time to recover function spontaneously before starting permanent replacement therapy. This can be difficult for the patient unless partial T4replacement is given. Unfortunately, one of the common side effects of treating hyperthyroidism is weight gain, averaging about 20 lbs through four years after treatment (64a). Patients may develop transient increases in FTI and T3 at 2-4 months after treatment [63.1], some