Objective: To assess the value of (18)F-FDG dual head coincidence imaging in the prediction of the efficacy of radioiodine therapy in patients with cervical lymph node (LN) metastasis of papillary thyroid carcinoma (PTC).
Methods: Thirty-six patients undergoing thyroidectomy and radioiodine ablation of the residual normal thyroid tissue received (18)F-FDG dual head coincidence imaging and then therapeutic (131)I-whole body imaging ((131)I-WBI) in the same week. According to those imaging results, the patients were divided into group I with positive results of both imaging examinations and group II with positive results by (131)I-WBI but negative results by(18)F-FDG dual head coincidence imaging. All the patients were followed up for 6 months.
Results: In group I (14 patients), a total of 49 lesions were diagnosed as cervical LN metastases, and the total sensitivity differed significantly between (18)F-FDG dual head coincidence imaging and (131)I- WBI (67.3% vs 89.8%, P=0.027). In both groups, the total sensitivity of (18)F-FDG dual head coincidence imaging and (131)I-WBI showed a significant difference (26.0% vs 94.5%, P<0.001). The target and non-target ratio (T/NT) was identified as one of the factors affecting the radioiodine efficacy (P<0.001). In group II (22 patients), 76 lesions were diagnosed as cervical LN metastases. The effective rates of groups I and II were 35.7% and 81.8%, respectively, showing a significant difference between them (P=0.011).
Conclusion: (131)I-WBI is more sensitive than (18)F-FDG dual head coincidence imaging in detecting cervical LN metastasis in patients with PTC. Patients with cervical LN metastases who have positive results in both (131)I-WBI and (18)F-FDG dual head coincidence imaging tend to have a poorer response to the therapy than the patients with negative results in (18)F-FDG dual head coincidence imaging. The T/NT of the cervical LN metastases in (18)F-FDG dual head coincidence imaging is associated with the efficacy of radioiodine therapy.