[Analysis of factors affecting treatment results for toxic goiter with radioactive 131I]

The aims of the study were to estimate the optimal dose (Gy) absorbed by pathological tissue and to establish factors influencing the results of treatment of hyperthyroidism. Data from 188 patients who underwent treatment with 131I between July 1991 and July 1994 were retrospectively analyzed. Thyroid status was examined after 1, 2.5, 6, 12, and 24 months. Following a thyroid scan, the whole group was divided into two subgroups: 72 cases of multifocal autonomy and 116 cases of solitary autonomous adenoma. The planimetric phantom for the whole thyroid or for nodules only was respectively used for unification of scintigraphic data. Administered dose (MBq) was converted into absorbed dose according to the Marinelli formula. The absorbed dose ranged between 11 and 1250 Gy (mean = 290 Gy). The results of treatment confirmed with laboratory tests were correlated with the absorbed dose, initial thyroid or nodular volume, initial level of free thyroxine, age, sex, and presence in the scintigram of active extranodular tissue. Two years after administration of radioiodine, 45 out of 72 patients with multifocal autonomy (62.5%) had normal thyroid status, 5 (6.9%) were hypothyroid and 22 (30.6%) remained hyperthyroid. For the group of 116 patients with solitary autonomous adenoma the respective result was 84 (72.4%), 16 (13.8%) and 16 (13.8%). When the absorbed dose in multifocal autonomy was less than 250 Gy the respective result was 27 (52.9%), 2 (3.9%), and 22 (43.1%). For a dose of 250 Gy or more the result was 18 (85.7%) patients with normal thyroid status, 3 (14.3%) hypothyroid, and none hyperthyroid (Tab. 2). The differences were statistically significant (p < 0.001). In the subgroup with solitary autonomous adenoma, for an absorbed dose of less than 350 Gy, 60 (71.5%) patients had normal thyroid status, 8 (9.5%) were hypothyroid, and 16 (19%) remained hyperthyroid. For a dose of 350 Gy or more, 24 (75%) patients had normal thyroid status, 8 (25%) were hypothyroid and none remained hyperthyroid (Tab. 3). The differences were statistically significant (p < 0.00025). The relationship between persistence of hyperthyroidism and thyroid (or nodular) volume or level of free thyroxine was directly proportional (p < 0.000001 and p < 0.00006). Superior results were obtained when the dose of radioiodine was calculated relative to the nodular rather than thyroid volume (p < 0.002). There was no correlation with active extranodular tissue, age or sex.

1. Treatment with radioiodine is a safe method offering good clinical results in 90% of patients. 2. The more accurate is the calculated dose, the better and faster is the result. 3. The optimal absorbed dose for multifocal autonomy is 250 Gy. 4. The optimal absorbed dose for solitary toxic adenoma is 350 Gy. 5. The greater is the thyroid or nodule volume and level of free thyroxine, the greater is the probability of persistent hyperthyroidism. 6. In case of persistent hyperthyroidism an additional radioiodine dose is recommended after six months. 7. Age, sex and presence of active extranodular tissue have no influence on the results of treatment.