CONTEXT:

Despite accounting for variations in gland size and iodine kinetics, the success of radioiodine therapy in patients with Graves' disease remains moderately common and unpredictable.

OBJECTIVES:

We hypothesized that hypoechogenic glands, with large, densely packed cells, are more radiosensitive than normoechogenic glands, in which much radiation is wasted on more abundant colloid. We evaluated this hypothesis in a cohort of patients with Graves' disease.

DESIGN:

This was a prospective trial of patients recruited during 4 yr and followed up 1 yr after radioiodine therapy.

SETTING:

This trial was held in a university hospital-outpatient clinic.

PATIENTS:

A total of 177 consecutive patients with first presentation of Graves' disease (28 males), 23-76 yr old, who relapsed after antithyroid therapy were included in the study.

INTERVENTION:

The patients were assigned to an ablative target-absorbed dose of 200 Gy (n = 78) or randomly to 100 or 120 Gy of nonablative dose (n = 99).

MAIN OUTCOME MEASURES:

The measures were incidences of hyperthyroidism, euthyroidism, and hypothyroidism at 12-month follow-up. Results: At follow-up there were 25 hyperthyroid, 44 euthyroid, and 108 hypothyroid patients. Compared with 96 patients with a hypoechogenic gland, in 81 patients with a normoechogenic gland, there were more hyperthyroid (22 vs. 7%) and euthyroid (41 vs. 11%), but less hypothyroid outcomes (37 vs. 81%; P < 0.0001). The other independent predictor of increased radioresistance was the large gland volume.

CONCLUSION:

In patients with Graves' disease, normoechogenic and large glands are associated with increased radioresistance.