Determination of the optimal minimum radioiodine dose in patients with Graves' disease: a clinical outcome study

Abstract

The study was performed under the auspices of the International Atomic Energy Commission, Vienna, Austria, with the aim of determining the optimal minimum therapeutic dose of iodine-131 for Graves' disease. The study was designed as a single-blinded randomised prospective outcome trial. Fifty-eight patients were enrolled, consisting of 50 females and 8 males aged from 17 to 75 years. Each patient was investigated by clinical assessment, biochemical and immunological assessment, thyroid ultrasound, technetium-99m thyroid scintigraphy and 24-h thyroid 131I uptake. Patients were then randomised into two treatment groups, one receiving 60 Gy and the other receiving 90 Gy thyroid tissue absorbed dose of radioiodine. The end-point markers were clinical and biochemical response to treatment. The median follow-up period was 37.5 months (range, 24-48 months). Among the 57 patients who completed final follow-up, a euthyroid state was achieved in 26 patients (46%), 27 patients (47%) were rendered hypothyroid and four patients (7%) remained hyperthyroid. Thirty-four patients (60%) remained hyperthyroid at 6 months after the initial radioiodine dose (median dose 126 MBq), and a total of 21 patients required additional radioiodine therapy (median total dose 640 MBq; range 370-1,485 MBq). At 6-month follow-up, of the 29 patients who received a thyroid tissue dose of 90 Gy, 17 (59%) remained hyperthyroid. By comparison, of the 28 patients who received a thyroid tissue dose of 60 Gy, 17 (61%) remained hyperthyroid. No significant difference in treatment response was found (P=0.881). At 6 months, five patients in the 90-Gy group were hypothyroid, compared to two patients in the 60-Gy group (P=0.246). Overall at 6 months, non-responders to low-dose therapy had a significantly larger thyroid gland mass (respective means: 35.9 ml vs 21.9 ml) and significantly higher levels of serum thyroglobulin (respective means: 597.6 microg/l vs 96.9 microg/l). Where low-dose radioiodine treatment of Graves' disease is considered, a dose of 60 Gy will yield a 39% response rate at 6 months while minimising early hypothyroidism. No significant advantage in response rate is gained by using a dose of 90 Gy. For more rapid therapeutic effect at the expense of an increased rate of hypothyroidism, doses in excess of 120 Gy may be required. Ultrasound determination of thyroid mass and measurement of serum thyroglobulin levels may be predictive of those patients who will be less responsive to low-dose therapy.

Radioiodine Treatment of Graves’ Disease – Dose/Response Analysis

“…This success rate was similar to those found by others with comparably high adjusted doses: 86% for ca 6.4 MBq/g [36], 85% for 7.4 MBq/g [27], 90% for 7.4 MBq/g [37], 72% for 7 MBq/g [38], 85% for 7.1 MBq/g [39]. Lower adjusted doses gave similarly lower cure rate: 39% for ca 2.1 MBq/g and 41% for ca 3.2 MBq/g [14], 50% for 3.7 MBq/g [24], 55% for 4.4 MBq/g [23]. Dose/ response relationship with several adjusted doses in the same group came from post hoc analysis of the "fixed dose" subgroup in the prospective study by Peters et al [16].…”

“…Still, there is little consensus regarding the most appropriate dosing regimen (2,9). While some prefer fixed doses of 5, 10, or 15 mCi (185, 370, or 555 MBq) for Graves' disease (10)(11)(12) others try to individualize the dose using calculations based on Quimby-Marinelli formula and dependent on the thyroid gland size and the 24-hour RAI uptake (13), or even effective RAI half-life measurement (14).…”

Resumption of methimazole after 131I therapy of hyperthyroid diseases: effect on thyroid function and volume evaluated by a randomized clinical trial

“…In addition, the correlation between the intended and the actual dose delivered to the thyroid is highly variable, with a mean coefficient of variation of 45% (27). It is therefore not surprising that susceptibility of the thyroid to a wide range of 131 I radiation shows huge individual variations (28).…”

Radioiodine therapy and Graves’ disease – Myths and reality

“…In the available literature, the average period of recurrence of hyperthyroidism after RIT in patients with GD from the moment of administration of the first therapeutic dose of 131 I is 6 months [22,23,[35][36][37][38][39][40][41]. Nwatsock J.F.…”