Reaching the target dose with one single 131I‐mIBG administration in high‐risk neuroblastoma: The determinant impact of the primary tumour

Abstract

AbstractBackground: 131I‐metaiodobenzylguanidine (131I‐mIBG) effectiveness in children with metastasised neuroblastoma (NB) is linked to the effective dose absorbed by the target; a target of 4 Gy whole‐body dose threshold has been proposed. Achieving this dose often requires administering 131I‐mIBG twice back‐to‐back, which may cause haematological toxicity. In this study, we tried identifying the factors predicting the achievement of 4 Gy whole‐body dose with a single radiopharmaceutical administration.Materials and methods: Children affected by metastatic NB and treated with a high 131I‐mIBG activity (>450 MBq (megabecquerel)/kg) were evaluated retrospectively. Kinetics measurements were carried out at multiple time points to estimate the whole‐body dose, which was compared with clinical and activity‐related parameters.Results: Seventeen children (12 females, median age 3 years, age range: 1.5–6.9 years) were included. Eleven of them still bore the primary tumour. The median whole‐body dose was 2.88 Gy (range: 1.63–4.22 Gy). Children with a ‘bulky’ primary (>30 mL) received a higher whole‐body dose than those with smaller or surgically removed primaries (3.42 ± 0.74 vs. 2.48 ± 0.65 Gy, respectively, p = .016). Conversely, the correlation between activity/kg and the whole‐body dose was moderate (R: 0.42, p = .093). In the multivariate analysis, the volume of the primary tumour was the most relevant predictor of the whole‐body dose (p = .002).Conclusions: These data suggest that the presence of a bulky primary tumour can significantly prolong the 131I‐mIBG biological half‐life, effectively increasing the absorbed whole‐body dose. This information could be used to model the administered activity, allowing to attain the target dose without needing a two‐step radiopharmaceutical administration.