Low versus high radioiodine dose in postoperative ablation of residual thyroid
tissue in patients with differentiated thyroid carcinoma: a large randomized
clinical trial.
Author(s): Fallahi B, Beiki D, Takavar A, Fard-Esfahani A, Gilani KA, Saghari M, Eftekhari
M.
Affiliation(s): Research Institute for Nuclear Medicine, Tehran University of Medical Sciences,
Tehran, Iran.
Publication date & source: 2012, Nucl Med Commun. , 33(3):275-82
OBJECTIVES: Radioiodine ablation of thyroid tissue remains the cornerstone of
treatment for patients with differentiated thyroid carcinoma after thyroidectomy.
Selecting an optimal dose of radioiodine for successful ablation is a continuous
challenge in these patients.
METHODS: We compared the treatment response of 341 patients with thyroidectomy
randomly allocated to the high-dose group, 3700 MBq (170 patients), versus the
low-dose group, 1110 MBq (171 patients), for radioiodine ablation therapy in a
double-blind randomized clinical trial. The response to treatment was defined as
successful or unsuccessful according to post-therapy ultrasonography of the neck,
serum thyroglobulin (Tg), anti-Tg, and functioning residual tissue after 6-month
and 12-month intervals. The major criteria of successful ablation were Tg<2
ng/ml, anti-Tg<100 IU/ml, and absent remnant in the off-levothyroxine state.
Additional radioiodine doses were administered in cases showing no significant
response to the first therapy. Finally, the initial outcome, the total
hospitalization time, and the cumulative I-131 doses during the 12-month course
of the study were compared between the subgroups.
RESULTS: The rate of initial successful ablation was 51.6% in all patients, 39.2%
in the low-dose group, and 64.1% in the high-dose group. The corresponding
success rates at the end of the 12-month follow-up without additional treatment
were 55.1, 41.5, and 68.8%, respectively. The relative risk (RR) of unsuccessful
ablation for the low-dose versus the high-dose group was 1.695 [95% confidence
interval (CI), 1.34-2.14]. In the low-dose group, more patients needed a second
dose of I-131, resulting in a higher cumulative activity (median, 4810 vs. 3700
MBq, P<0.0001) and more inpatient time (median 4 vs. 3 days) in comparison with
the high-dose group. The covariate factors predicting the treatment response, in
order of significance, were radioiodine dose, baseline Tg, baseline thyroid
stimulating hormone (TSH) level, efficiency of TSH suppressive therapy, and sex.
CONCLUSION: The higher dose of I-131 (3700 MBq) resulted in successful ablation
more often than the low dose (1110 MBq).
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