Head and Neck Neoplasms/prevention & control; Iodine Radioisotopes/administration & dosage; Neck Dissection; Neoplasm Recurrence, Local/prevention & control; Radiopharmaceuticals/administration & dosage; Thyroid Neoplasms/radiotherapy; Thyroidectomy; Adult; Aged; Cohort Studies; Dose-Response Relationship, Radiation; Female; Follow-Up Studies; Head and Neck Neoplasms/diagnostic imaging; Head and Neck Neoplasms/epidemiology; Head and Neck Neoplasms/secondary; Humans; Iodine Radioisotopes/therapeutic use; Male; Middle Aged; Neck/diagnostic imaging; Neck/pathology; Neck/radiation effects; Neck/surgery; Neoplasm Recurrence, Local/epidemiology; Neoplasm Staging; Radiopharmaceuticals/therapeutic use; Radiotherapy, Adjuvant; Republic of Korea/epidemiology; Retrospective Studies; Risk Factors; Thyroid Gland/diagnostic imaging; Thyroid Gland/pathology; Thyroid Gland/surgery; Thyroid Neoplasms/pathology; Thyroid Neoplasms/prevention & control; Thyroid Neoplasms/surgery; Tumor Burden/radiation effects; Ultrasonography