Tumor Dosimetry Using [124I]m-iodobenzylguanidine MicroPET/CT for [131I]m-iodobenzylguanidine Treatment of Neuroblastoma in a Murine Xenograft Model
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- Seo, Y., Gustafson, W.C., Dannoon, S.F. et al. Mol Imaging Biol (2012) 14: 735. doi:10.1007/s11307-012-0552-4
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[124I]m-iodobenzylguanidine (124I-mIBG) provides a quantitative tool for pretherapy tumor imaging and dosimetry when performed before [131I]m-iodobenzylguanidine (131I-mIBG) targeted radionuclide therapy of neuroblastoma. 124I (T1/2 = 4.2 days) has a comparable half-life to that of 131I (T1/2 = 8.02 days) and can be imaged by positron emission tomography (PET) for accurate quantification of the radiotracer distribution. We estimated expected radiation dose in tumors from 131I-mIBG therapy using 124I-mIBG microPET/CT imaging data in a murine xenograft model of neuroblastoma transduced to express high levels of the human norepinephrine transporter (hNET).
In order to enhance mIBG uptake for in vivo imaging and therapy, NB 1691-luciferase (NB1691) human neuroblastoma cells were engineered to express high levels of hNET protein by lentiviral transduction (NB1691-hNET). Both NB1691 and NB1691-hNET cells were implanted subcutaneously and into renal capsules in athymic mice. 124I-mIBG (4.2–6.5 MBq) was administered intravenously for microPET/CT imaging at 5 time points over 95 h (0.5, 3–5, 24, 48, and 93–95 h median time points). In vivo biodistribution data in normal organs, tumors, and whole-body were collected from reconstructed PET images corrected for photon attenuation using the CT-based attenuation map. Organ and tumor dosimetry were determined for 124I-mIBG. Dose estimates for 131I-mIBG were made, assuming the same in vivo biodistribution as 124I-mIBG.
All NB1691-hNET tumors had significant uptake and retention of 124I-mIBG, whereas unmodified NB1691 tumors did not demonstrate quantifiable mIBG uptake in vivo, despite in vitro uptake. 124I-mIBG with microPET/CT provided an accurate three-dimensional tool for estimating the radiation dose that would be delivered with 131I-mIBG therapy. For example, in our model system, we estimated that the administration of 131I-mIBG in the range of 52.8–206 MBq would deliver 20 Gy to tumors.
The overexpression of hNET was found to be critical for 124I-mIBG uptake and retention in vivo. The quantitative 124I-mIBG PET/CT is a promising new tool to predict tumor radiation doses with 131I-mIBG therapy of neuroblastoma. This methodology may be applied to tumor dosimetry of 131I-mIBG therapy in human subjects using 124I-mIBG pretherapy PET/CT data.