124I-MIBG PET/CT to Monitor Metastatic Disease in Children with Relapsed Neuroblastoma.

The metaiodobenzylguanidine (MIBG) scan is one of the most sensitive noninvasive lesion detection modalities for neuroblastoma. Unlike 123I-MIBG, 124I-MIBG allows high-resolution PET. We evaluated 124I-MIBG PET/CT for its diagnostic performance as directly compared with paired 123I-MIBG scans. Methods: Before 131I-MIBG therapy, standard 123I-MIBG imaging (5.2 MBq/kg) was performed on 7 patients, including whole-body (anterior-posterior) planar imaging, focused-field-of-view SPECT/CT, and whole-body 124I-MIBG PET/CT (1.05 MBq/kg). After therapy, 2 of 7 patients also completed 124I-MIBG PET/CT as well as paired 123I-MIBG planar imaging and SPECT/CT. One patient underwent 124I-MIBG PET/CT only after therapy. We evaluated all 8 patients who showed at least 1 123I-MIBG-positive lesion with a total of 10 scans. In 8 pairs, 123I-MIBG and 124I-MIBG were performed within 1 mo of each other. The locations of identified lesions, the number of total lesions, and the curie scores were recorded for the 123I-MIBG and 124I-MIBG scans. Finally, for 5 patients who completed at least 3 PET/CT scans after administration of 124I-MIBG, we estimated the effective dose of 124I-MIBG. Results:123I-MIBG whole-body planar scans, focused-field-of-view SPECT/CT scans, and whole-body 124I-MIBG PET scans found 25, 32, and 87 total lesions, respectively. There was a statistically significant difference in lesion detection for 124I-MIBG PET/CT versus 123I-MIBG planar imaging (P < 0.0001) and 123I-MIBG SPECT/CT (P < 0.0001). The curie scores were also higher for 124I-MIBG PET/CT than for 123I-MIBG planar imaging and SPECT/CT in 6 of 10 patients. 124I-MIBG PET/CT demonstrated better detection of lesions throughout the body, including the chest, spine, head and neck, and extremities. The effective dose estimated for patient-specific 124I-MIBG was approximately 10 times that of 123I-MIBG; however, given that we administered a very low activity of 124I-MIBG (1.05 MBq/kg), the effective dose was only approximately twice that of 123I-MIBG despite the large difference in half-lives (100 vs. 13.2 h). Conclusion: The first-in-humans use of low-dose 124I-MIBG PET for monitoring disease burden demonstrated tumor detection capability superior to that of 123I-MIBG planar imaging and SPECT/CT.