Local and regional control in patients with papillary thyroid carcinoma: specific indications of external radiotherapy and radioactive iodine according to T and N categories in AJCC 6th edition

To identify indications for external radiotherapy (EXT) and radioactive iodine (RAI) in papillary thyroid carcinoma (PTC), we conducted a retrospective study of local and regional control in 1297 patients diagnosed with PTC in a tertiary referral center. Managed by surgery alone, patients with bilateral thyroidectomy had a lower rate of local relapse compared with lobectomy (P= 0.02). EXT improved locoregional (LR) failure-free survival (FFS) (P < 0.001) and survival (P=0.01) in patients with gross postoperative LR residual disease. EXT also improved local FFS in patients with pathologically confirmed positive resection margins (P < 0.001) and reduced local failures in patients with T4 disease (P=0.002). In patients with lymph nodes (LN) metastasis, more extensive surgery by functional or radical neck dissection resulted in less LN relapse compared with excision alone (P < 0.001). EXT improved 10-year LN FFS in patients with N1b disease (P=0.005) and patients with LN metastasis of size > 2cm (P=0.02). RAI was effective in improving local control in patients with T2 to T4 diseases and LN control in patients with N0, N1a, and N1b categories. Local or LN relapses were associated with worse survival (P < 0.001 and P < 0.0001). The survival of patients with PTC could be improved by reducing local or LN relapses. RAI is indicated in patients with T2 to T4 disease. EXT is indicated in patients with gross postoperative disease, positive resection margins or T4 disease, N1b, or a LN size of > 2cm. LN relapse can be reduced by RAI in N0, N1a, and N1b disease.