Assessment of radioiodine therapy efficacy for treatment of differentiated thyroid cancer patients with pulmonary metastasis undetected by chest computed tomography

Radioiodine therapy (RAI) has proven effective for the treatment of patients exhibiting differentiated thyroid cancer (DTC) with pulmonary metastases. However, the early detection of metastasis remains challenging, and various studies have reported variations in radioiodine treatment efficacy. The present study investigated whether RAI is an effective method for the treatment of DTC with pulmonary metastases undetected by computed tomography (CT). A retrospective study was performed, analyzing iodine-131 (131I) therapy in 21 DTC patients with lung metastases that were undetected by CT. All 21 patients were initially treated with radioiodine ablation of thyroid remnants. Routine chest CT was performed prior to 131I treatment without diagnostic radioiodine whole-body scanning (DxWBS), and post-therapeutic WBS was performed 3-5 days subsequent to oral administration of 131I. The overall effectiveness rate was 95.2% (20/21). The rates for complete response (CR), partial response and no response were 23.8 (5/21), 71.4 (15/21) and 4.8% (1/21), respectively. There were 12 patients with diffuse uptake, and the remaining 9 patients demonstrated focused and low uptake. The difference in CR rate between diffuse uptake and focused uptake patients was not statistically significant (P=0.123). A correlation was observed between thyroglobulin (Tg) levels and extrapulmonary metastases. All patients exhibited extrapulmonary metastases when Tg levels were >87.5 ng/ml (area under receiver operating characteristic curve, 1.0; P<0.001). Overall, DTC patients with lung metastases undetected by CT imaging responded well to 131I radiotherapy and demonstrated a positive prognosis. Serum Tg levels prior to 131I treatment may correlate with metastasis, and this may suggest a requirement for the performance of DxWBS prior to radiotherapy.