Impact of 131I-MIBG dose escalation (12 vs. 18 mCi/kg) during conditioning for autologous hematopoietic stem cell transplantation in pediatric neuroblastoma: a retrospective cohort study.

UNLABELLED: This study aimed to evaluate whether dose escalation of 131I-meta-iodobenzylguanidine (131I-MIBG) from 12 to 18 mCi/kg improves survival, engraftment, or toxicity profiles in children with high-risk neuroblastoma undergoing autologous HSCT. We retrospectively analyzed 56 pediatric patients under 18 years of age with high-risk, MIBG-avid neuroblastoma who underwent autologous HSCT between 2016 and 2025. Patients received either 12 mCi/kg (n = 17) or 18 mCi/kg (n = 39) of 131I-MIBG as part of a myeloablative chemotherapy conditioning regimen. Outcomes included engraftment, overall survival (OS), and event-free survival (EFS). Twenty-one deaths had occurred (8/17 [47.1%] in the 12 mCi/kg group; 13/39 [33.3%] in the 18 mCi/kg group). OS at 1 and 5 years was 76.5% and 59.5% for the 12 mCi/kg group, compared with 76.6% and 58.2% for the 18 mCi/kg group (log-rank p = 0.786). EFS at 1 and 5 years was 45.3% and 38.8% for the 12 mCi/kg group, compared with 69.1% and 36.2% for the 18 mCi/kg group (log-rank p = 0.656). Furthermore, at 1-year post-HSCT, the 18 mCi/kg group demonstrated a significantly higher rate of normal MIBG scans (83.3% vs. 46.2%, p = 0.024). Neutrophil engraftment was faster in the 18 mCi/kg group (median 10 vs 12 days; p = 0.001). Platelet engraftment was also more frequent in the 18 mCi/kg group (92.3% vs 70.6%; p = 0.047), with similar time to engraftment (16 vs 16.5 days).

CONCLUSION

In this retrospective cohort, escalation from 12 to 18 mCi/kg was associated with faster neutrophil engraftment and a higher rate of normal MIBG scans at 1 year, without a significant difference in OS or EFS. The study was underpowered, and did not demonstrate a significant benefit of either the lower or the higher dose; the optimal dose remains undetermined and requires prospective evaluation.

WHAT IS KNOWN: • 131I-MIBG is incorporated into conditioning regimens prior to autologous HSCT for high-risk pediatric neuroblastoma, with doses up to 18 mCi/kg being tolerable, but the optimal dose and its impact on long-term survival remain unclear.

WHAT IS NEW: • In this direct retrospective comparison (12 vs. 18 mCi/kg), the higher dose was associated with faster neutrophil engraftment and a higher platelet engraftment rate and a higher rate of normal MIBG scans at year, but without a significant difference in OS or EFS, and with a non-significant trend toward more renal and thyroid toxicity. The study was underpowered and did not demonstrate a significant benefit of either dose; the optimal MIBG dose remains undetermined.