Patients with stage III and IV differentiated thyroid cancer; all stage II patients <45 years of age; most stage II patients >45 years of age; selective stage I patients, especially those with multiple tumor foci, lymph node metastases, extra-thyroidal or vascular infiltration; and patients with aggressive pathological types. In more general terms, the following conditions require nail-cleaning therapy: patients with DTC who have developed distant metastases, or extra-thyroidal invasion, or a primary lesion >4 cm; patients without extra-thyroidal invasion, with a primary lesion of 1-4 cm at intermediate and high risk; and patients with a single lesion of <1 cm in diameter or multiple lesions of <1 cm in diameter, without risk factors, who are exempted from 131I nail-cleansing therapy for the time being.