Radiation dose estimation using preclinical imaging with 124I-metaiodobenzylguanidine (MIBG) PET.
OBJECTIVE
A pretherapy 124I-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 131I-MIBG treatment of neuroblastoma or pheochromocytoma. The aim of this work was to estimate human-equivalent internal radiation dose of 124I-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 (approximate imaging time points: 0.5, 2, 24, 52, and 96 h) after intravenous administration of 3.07-4.84 MBq of 124I-MIBG via tail vein. The tumors did not accumulate 124I-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 OLINDA/EXM software with modified tissue weighting factors in the recent International Commission on Radiological Protection (ICRP) Publication 103.


RESULTS
The mean effective dose from 124I-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 124I-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 124I-MIBG using preclinical imaging data. As a reference, the effective dose estimation showed that 124I-MIBG would deliver less radiation dose than 124I-NaI, a radiotracer already being used in patients with thyroid cancer.
Lee
Chang-Lae
CL
Department of Radiology and Biomedical Imaging, UCSF Physics Research Laboratory, University of California, San Francisco, San Francisco, California 94143, USA.
Wahnishe
Hilla
H
Sayre
George A
GA
Cho
Hyo-Min
HM
Kim
Hee-Joung
HJ
Hernandez-Pampaloni
Miguel
M
Hawkins
Randall A
RA
Dannoon
Shorouk F
SF
VanBrocklin
Henry F
HF
Itsara
Melissa
M
Weiss
William A
WA
Yang
Xiaodong
X
Haas-Kogan
Daphne A
DA
Matthay
Katherine K
KK
Seo
Youngho
Y
D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics; D000293:Adolescent; D000328:Adult; D000818:Animals; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed
D019797:3-Iodobenzylguanidine