Abstract:
The destruction of thyroid follicular cells by iodine-131 treatment for Graves’ hyperthyroidism to a large extent
depends on the amount of intrathyroidal activity absorbed (IAA). A thyroid weighing 50 g should receive an iodine-131
therapeutic dosage of between 110 MBq and 350 MBq for the effective treatment of Graves’ hyperthyroidism. An IAA
received of more than 350 MBq to the thyroid will bestow an unnecessary high iodine-131 therapeutic dosage. The objective
of the study was to determine if the IAA would remain between 110 MBq and 350 MBq if the calculated administered activity
(CAA) has been used with the highest radioactive iodine uptake (RAIU) value. A retrospective analysis was made of the 6-
and 24-hr iodine-131 RAIU results of Graves’ hyperthyroid patients (n = 124). Male (n = 18) and female (n = 106) patients
from different racial groups and ranging from 15 to 75 years of age were included in the study. Overall, the CAA using the 6-
hr RAIU value was higher. The CAA by the 6-hr RAIU values was used with the 24-hr RAIU values to calculate the IAA.
53.3% (n = 66) of the study group would have received IAA higher than 350 MBq when the CAA by the 6-hr RAIU values
was used with the 24-hr RAIU values to calculate the IAA. These results suggested that the 24-hr RAIU value was most
valuable for the calculation of an administered activity so that IAA of between 110 and 350 MBq can be achieved.
