Tumor dosimetry of ¹³¹I-MIBG in animal models of neuroblastoma using ¹²⁴I-MIBG and microPET/CT

Objectives ¹²⁴I-MIBG provides a quantitative tool for pretherapy dosimetry when performed before ¹³¹I-MIBG therapy of neuroblastoma. ¹²⁴I has a comparable half-life (4.2d) to that of ¹³¹I (8.02d), and is imaged by PET. Using animal models of neuroblastoma, we estimated radiation dose expected from ¹³¹I-MIBG therapy using ¹²⁴I-MIBG microPET/CT.

Methods In order to evaluate the correlation of the degree of the human norepinephrine transporter (hNET) expression and ¹²⁴I-MIBG uptake, we developed a mouse model with NB1691, a neuroblastoma cell line expressing a high level of hNET, xenografted on two shoulders, one having hNET-overexpressed cells and the other unmodified cells. After substantial growth of tumors in athymic mice (n=6), ¹²⁴I-MIBG was administered intravenously for microPET/CT at 0.5, 3, 24, 48, and 96 h postinjection. In vivo biodistribution data in organs, tumors, and whole-bodies were collected from reconstructed PET/CT images. Organ and tumor dosimetry was performed for ¹²⁴I-MIBG, followed by the dosimetric evaluations for ¹³¹I-MIBG assuming the same biodistribution.

Results All hNET-overexpressed NB1691 xenograft tumors had significant uptake of ¹²⁴I-MIBG, but unmodified xenografts did not have any quantifiable MIBG uptake. Tumor dosimetry indicated that 3.69-170 MBq of ¹³¹I-MIBG was required to deliver therapeutic radiation of 60 Gy to tumors.

Conclusions The hNET expression was highly correlative with ¹²⁴I-MIBG uptake. The quantitative ¹²⁴I-MIBG PET/CT is a promising new tool to improve the planning of ¹³¹I-MIBG therapy of neuroblastoma