Estimate Thyroid Absorbed Dose Using I-123 MIBG Imaging | 12287
OMICS Journal of Radiology
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To evaluate use of thyroid blockade prior to AdreView Iobenguane I-123 (GE HealthCare) injection by estimating
radiation absorbed dose to patients with I-123 MIBG gamma camera imaging.
A hundred and five patients were administrated with I-123 MIBG, 370 MBq each for adults and adjusted per weight
for pediatric patients, through intravenous injection. No thyroid blockade (Potassium Iodide Oral Solution) was used prior to
the I-123 injection. Some of the patients had contrast from CT scans before the gamma camera imaging. Whole body planar
imaging was performed 24 hours following administration of the radiopharmaceutical. Dual head gamma cameras with LEHR
collimators were used to obtain anterior and posterior scans simultaneously. 15% energy window centered at 159 keV was set and
scan speed was 9 cm/min. Region of interest (RoI) was defined manually for thyroid and for whole body as well. Geometric mean
of the RoI counts from anterior and posterior views was used to calculate absorbed dose. Calibration factor was obtained using
total body counts and injected activity. This was done in two ways: using each patient or average of twenty patients. Using the
averaged total body counts to generate a single calibration factor would reduce statistical uncertainty. Internal dosimetry software
(Olinda/EXM 1.1) was also used to compare the doses. Numbers of disintegrations per unit activity (hr) entered to the Olinda
was 17.6 hours based on 25% thyroid uptake.
Average effective dose was 49 mrem for whole body and 2.34 mrem for thyroid with the single calibration factor. If
individual calibration factors were used, the average effective dose was 207 mrem for whole body and 2.72 for thyroid. The Olinda
dosimetry program yielded an effective dose 48 mrem.
Gamma camera imaging of I-123 MIBG provided an estimate to thyroid absorbed dose. Accuracy of the dosimetry
depends on quantification of the images and calibration factor. The thyroid blockade may not be necessary.
Jianqiao Luo joined the Physics and Biology Division of the Department of Radiology in October 2007. He is a clinical nuclear medicine faculty at
VCU and radiation safety officer for Hunter Holmes McGuire VA Medical Center. Prior to that, Luo was a nuclear medicine physicist in St. Vencent
Medical Center in New York and appointed clinical assistant professor in Medical College of New York in 1995. He also served as medical physicist
in Northwestern Memorial Hospital in Chicago from 2004 to 2007. Luo completed his research project on Monte Carlo Simulation for Compton
Scattering Correction in SPECT in University of Michigan Medical Center and received his Ph.D. in Medical Physics in 1993 from Oakland University.
His clinical activities include SPECT/PET imaging and radionuclide therapy. Luo is involved in a number of research projects and clinical trials on
nuclear medicine imaging (SPECT, PET and PET-CT) - quantification, artifacts. Molecular imaging (microSPECT, nanoSPECT and microPET) -
imaging protocol, instrumentation and data analysis, and internal dosimetry for therapy procedures.
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