Minimize Radioactive Iodine Ablation Of Remnant Thyroid in Differentiated Thyroid Cancer

Inclusion Criteria: * patients with differentiated thyroid cancer * recently underwent total thyroidectomy (within 6 months) * pathological criteria 1. T1bN0 : Tumor size 1-2cm with no microscopic extension with multifocality (within three foci) 2. T3N0 : Tumor size \<=2cm with microscopic extension (less than strap muscle) 3. T1-3N1a : 3 or less micrometastatic lymph node Exclusion Criteria: * differentiated thyroid cancer with aggressive variant, poorly differentiated thyroid cancer, medullary thyroid cancer, anaplastic thyroid cancer * gross extension (strap muscle or more) * thyroid cancer with distant metastasis * previous remote history of thyroid cancer surgery * history of cervical external beam radiation therapy * previous history of comorbid cancer within 5 years * renal insufficiency (Ccr \<30ml/min) * women with pregnancy or breast feeding