Low dose I-123 MIBG diagnostic scan is inferior to I-131 MIBG post-treatment scan in detection of neuroblastoma

Objectives I-123 MIBG scan is useful for detecting primary and metastatic lesions of neuroblastoma. However, we had experienced that the findings of I-123 MIBG scan were different from those of post-treatment I-131 MIBG image. One of reasons was that only a low dose at a maximum of 111 MBq of I-123 MIBG was available for diagnosis in Japan. In this study, we compared diagnostic I-123 MIBG scan with post-treatment I-131 MIBG scan in patients with neuroblastoma.

Methods We compared a total of 20 I-123 MIBG scans with their post-treatment I-131 MIBG scans in patients with neuroblastoma. Diagnostic scans with 74-111 MBq of I-123 MIBG were performed. After 5-28 days (median = 13.4 days) of I-123 MIBG scans, therapeutic dose of I-131 MIBG (3.7-14.8 GBq, median= 7.7 GBq) were administrated and whole body scans were obtained at 2-5 days after I-131 MIBG administrations. At least two nuclear medicine physicians evaluated the number of accumulations in the following sites; bone, liver, lymph node, and others.

Results With diagnostic I-123 MIBG scans, one or more lesions were detected in all patients. Post-treatment I-131 MIBG scans revealed new lesions in 13 (65%) of 20 patients. I-123 MIBG scans were not superior to I-131 MIBG scans in any cases. I-123 MIBG scans were disconcordant with those of corresponding post-treatment I-131 MIBG scans in 9 (47%) of 19 patients with bone metastases, 1 (33%) of 3 patients with liver metastases, 4 (50%) of 8 patients with lymph node metastases, and 3 (33%) of 9 patients with metastases in others.

Conclusions Diagnostic scintigraphy with low dose I-123 MIBG is low concordance rate with post treatment I-131 MIBG image in patients with neuroblastoma