Utility of I-124 PET/CT in identifying radioiodine avid lesions in differentiated thyroid cancer: a systematic review and meta-analysis

IntroductionDiagnostic I-123 scans have been shown to underestimate the disease burden in differentiated thyroid cancer (DTC) when compared to I-131 post-treatment scans, especially in children and patients who have had prior radioiodine (RAI) therapy and/or distant metastasis. I-124 PET/CT has been shown to be highly effective in imaging DTC-related metastatic disease. MethodsWe performed a systematic review and meta-analysis of studies investigating the sensitivity and specificity of I-124 PET/CT in identifying lesions amenable to RAI therapy as confirmed by I-131 post-treatment scanning. ResultsThere were 141 patients and 415 lesions of DTC identified altogether. There was significant heterogeneity in the individual studies. The pooled sensitivity of the I-124 PET/CT in detecting lesions of differentiated thyroid cancer amenable to I-131 therapy was 94<bold></bold>2% (91<bold></bold>3-96<bold></bold>4% CI, P < 0<bold></bold>01), and the pooled specificity was 49<bold></bold>0% (34<bold></bold>8-63<bold></bold>4% CI, P < 0<bold></bold>01). The pooled positive likelihood ratio (LR) was 1<bold></bold>43 (1<bold></bold>05-1<bold></bold>94 CI), and the pooled negative LR was 0<bold></bold>28 (0<bold></bold>15-0<bold></bold>53 CI). Overall, the diagnostic odds ratio was 7<bold></bold>90 (3<bold></bold>39-18<bold></bold>48 CI). There were a small but increased number of lesions identified by I-124 PET/CT that was not detected on post-treatment scan. ConclusionI-124 PET/CT is a sensitive tool to diagnose RAI avid DTC lesions, but also detects some new lesions that are not visualized on the post-treatment I-131 scan. Further, carefully designed dosimetric studies may be required to fully establish the role of I-124 PET CT for identifying potential lesions for I-131 therapy. I-124 PET/CT in patients with DTC may have other applications in specific clinical situations.