Radiation dose estimation using preclinical imaging with 124I-metaiodobenzylguanidine (MIBG) PET

Purpose: A pretherapy I-124-metaiodobenzylguanidine (MIBG) positron emission tomography (PET)/computed tomography (CT) provides a potential method to estimate radiation dose to normal organs, as well as tumors prior to I-131-MIBG treatment of neuroblastoma or pheochromocytoma. The aim of this work was to estimate human-equivalent internal radiation dose of I-124-MIBG using PET/CT data in a murine xenograft model. Methods: Athymic mice subcutaneously implanted with NB1691 cells that express high levels of human norepinephrine transporter (n=4) were imaged using small animal microPET/CT over 96 h (appoximate imaging time points: 0.5, 2, 24, 52, and 96 h) after intravenous administration of 3.07-4.84 MBq of I-124-MIBG via tail vein. The tumors did not accumulate I-124-MIBG to a detectable level. All four animals were considered as control and organ radiation dosimetry was performed. Volumes of interest were drawn on the coregistered CT images for thyroid, heart, lung, liver, kidney, and bladder, and transferred to PET images to obtain pharmacokinetic data. Based on tabulated organ mass distributions for both mice and adult male human, preclinical pharmacokinetic data were extrapolated to their human-equivalent values. Radiation dose estimations for different age groups were performed using the OLINDAIEXM software with modified tissue weighting factors in the recent International Commission on Radiological Protection (ICRP) Publication 103. Results: The mean effective dose from I-124-MIBG using weighting factors from ICRP 103 to the adult male was estimated at 0.25 mSv/MBq. In different age groups, effective doses using values from ICRP 103 were estimated as follows: Adult female: 0.34, 15-yr-old: 0.39 mSv/MBq, 10-yr-old: 0.58 mSv/MBq, 5-yr-old: 1.03 mSv/MBq, 1-yr-old: 1.92 mSv/MBq, and newborn: 3.75 mSv/MBq. For comparison, the reported effective dose equivalent of I-124-NaI for adult male (25% thyroid uptake, MIRD Dose Estimate Report No. 5) was 6.5 mSv/MBq. Conclusions: The authors estimated human-equivalent internal radiation dose of I-124-MIBG using preclinical imaging data. As a reference, the effective dose estimation showed that I-124-MIBG would deliver less radiation dose than I-124-NaI, a radiotracer already being used in patients with thyroid cancer. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3480965]