In some patients, residual thyroid cannot be completely removed by a single treatment. This is most commonly seen when there is more residual thyroid tissue prior to nail clearance therapy, or when there is inadequate uptake of 131I by the residual thyroid tissue and DTC lesions (mostly due to the presence of large amounts of stable iodine in the body), or when the dose of 131I used for nail clearance is insufficient, or when there is a low sensitivity to 131I radiation. After 4-6 months of nail-clearing therapy, an assessment of whether nail-clearing is complete can be performed. If no thyroid tissue is visualized in the Dx-WBS image after TSH stimulation, and the rate of thyroid aspiration of 131I is <1%, it suggests that the 131I nail clearance is complete. Serum Tg testing and thyroid ultrasonography may also assist in determining whether nail clearance is complete. For those who still have residual thyroid tissue after the first nail clearance, a second nail clearance may be performed to achieve the goal of complete nail clearance. The 131I dose determination for repeat nail removal is based on the same principles as the first treatment. However, some researchers believe that if no abnormal 131I uptake outside the thyroid gland is seen by Rx-WBS in these patients after the first nail clearance, and if the dynamic monitoring of serum Tg is consistently <1 ng/mL and there is no obvious abnormality in the neck ultrasound, then there is no need to carry out a second nail clearance.