Description: Integrin α v β 3 has been proposed as a potential imaging target for radiolabeled RGD peptides and a molecular marker for the estimation of tumor angiogenesis, yet it has not been applied in differentiated thyroid cancer (DTC) patients with radioactive iodine–refractory (RAIR) lesions. The current study was conducted to assess the potential of integrin α v β 3 imaging in the detection of RAIR DTC lesions using 99m Tc-PEG 4 -E[PEG 4 -c(RGDfK)] 2 ( 99m Tc-3PRGD2), thus providing a feasible antiangiogenetic therapeutic target. Methods: Ten DTC patients (2 men, 8 women; mean age ± SD, 56.4 ± 9.8 y; age range, 42–73 y) with multiple RAIR metastases were recruited; all patients had both elevated thyroglobulin levels (thyroglobulin-positive) and negative 131 I whole-body scan (WBS) results. Clinical data were collected including history, 131 I WBS, contemporary CT, ultrasonography, thyroid-stimulating hormone, thyroglobulin, and antithyroglobulin. One or 2 target lesions were selected on the contemporary CT images using Response Evaluation Criteria in Solid Tumors 1.0 for all patients, 7 of whom were chosen for the calculation of the rates of lesion growth within the 3 mo before the study. WBS at 30 min and regional SPECT for lesions at 1 h were performed after the intravenous injection of 99m Tc-3PRGD2. Two experienced nuclear medicine physicians read the images in a masked fashion. The tumor-to-background ratios were calculated for further analysis. Results: All the target RAIR metastatic lesions were identified as positive on 99m Tc-3PRGD2 SPECT images. There was a significant correlation between the mean tumor-to-background ratios and mean growth rates of target lesions ( r = 0.878, P = 0.009). Conclusion: The RAIR ( 131 I WBS–negative/thyroglobulin-positive) metastatic lesions can be traced using 99m Tc-3PRGD2 imaging, meaning these lesions are highly neovascularized. 99m Tc-3PRGD2 angiogenesis imaging can be used for the localization and growth evaluation of RAIR lesions, providing a new therapeutic target and a novel imaging modality to monitor the efficacy of certain antiangiogenetic therapy.