HIGH-DOSE RADIOIODINE THERAPY IN ADVANCED DIFFERENTIATED THYROID-CARCINOMA

There is yet no consensus concerning the appropriate regimen of the ap plication of [(131)]sodium iodine (Nal) activities to patients sufferi ng from advanced differentiated thyroid carcinoma. We report on a tota l of 167 applications of [I-131]Nal, including 78 applications of 11.1 GBq. Response to high-activity radioiodine therapy (RIT) is correlate d to the course of the disease as well as to the reaction of thyreoglo bulin and acute/subacute side effects of radiation. Methods: Following radioablation of thyroid remnants using 1.85 to 3.7 GBq [I-131]Nal, 2 6 patients with advanced differentiated thyroid carcinoma (follicular, 11; papillary, 4; mixed-cell thyroid carcinoma, 11) were treated with repeated activities of 11.1 GBq [I-131]Nal. Initial tumor staging acc ording to UICC showed T4 in 54%, T3 in 19%, T2 in 19% and was not obta ined in 8%. Differentiated thyroid carcinoma was multifocal in 23% of patients. Applied accumulated activities ranged from 14.8 to 99.9 GBq with a mean of 55.5 GBq per patient. Results: Mean post-diagnostical f ollow-up was 73 mo, mean follow-up after diagnosis of metastatic sprea d was 48 mo. Follicular thyroid carcinoma remained as stable disease i n 7 of 11 patients, 6 of whom showed metastatic disease after a mean o f 20 mo, and only I complete remission was achieved using high-dose th erapies, with progressive disease in the remaining patients. Overall, 73% of follicular thyroid carcinoma had progressive disease without ma jor response to high-activity RIT. In contrast, only 20% of papillary thyroid carcinoma/mixed-cell thyroid carcinoma showed progressive dise ase, and complete remission was achieved in 47% of patients. Pulmonary and lymph node metastases in the majority of patients showed good res ponse to therapy, whereas local recurrences and bone metastases showed minor reactions to RIT. After low-activity therapies 8% of patients s howed WHO grade I hematotoxic reactions. After high-activity therapies , 38% of patients had WHO I, 8% WHO II and one patient had WHO III tox icity (4%). Conclusion: Use repetitive high-activity RIT with a maximu m of 44.4 GBq applied during 1 yr and a maximum of 99.9 GBq accumulate d activity resulted in a significant increase of hematotoxicity. Howev er, during the follow-up period (mean, 4 yr), no clinical symptoms pos sibly related to low blood counts were seen in patients with advanced differentiated thyroid carcinoma. Initiation of high-activity RIT in r eaction to metastatic tumor outspread to achieve complete remission wa s found to be useful in treating papillary thyroid carcinoma and mixed -cell thyroid carcinoma, but only in a minority of follicular thyroid carcinoma patients.