| ORIGINAL ARTICLE |
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| Year : 2016 | Volume
: 15
| Issue : 2 | Page : 114-123 |
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A 3D Monte Carlo method for estimation of patient-specific internal organs absorbed dose for 99m Tc-hynic-Tyr 3 -octreotide imaging
Mehdi Momennezhad1, Shahrokh Nasseri2, Seyed Rasoul Zakavi3, Ali Asghar Parach4, Mahdi Ghorbani1, Ruhollah Ghahraman Asl1
1 Department of Medical Physics, Faculty of Medicine, University of Medical Sciences, Mashhad, Iran
2 Department of Medical Physics, Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
3 Department of Nuclear Medicine, Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
4 Department of Medical Physics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Correspondence Address:
Ruhollah Ghahraman Asl
Department of Medical Physics, Faculty of Medicine, Mashhad University of Medical Sciences, Pardis -e Daneshgah, Vakil Abad Blvd., Mashhad
Iran
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DOI: 10.4103/1450-1147.174700 PMID: 27134562 
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Single-photon emission computed tomography (SPECT)-based tracers are easily available and more widely used than positron emission tomography (PET)-based tracers, and SPECT imaging still remains the most prevalent nuclear medicine imaging modality worldwide. The aim of this study is to implement an image-based Monte Carlo method for patient-specific three-dimensional (3D) absorbed dose calculation in patients after injection of 99m Tc-hydrazinonicotinamide (hynic)-Tyr 3 -octreotide as a SPECT radiotracer. 99m Tc patient-specific S values and the absorbed doses were calculated with GATE code for each source-target organ pair in four patients who were imaged for suspected neuroendocrine tumors. Each patient underwent multiple whole-body planar scans as well as SPECT imaging over a period of 1-24 h after intravenous injection of 99m hynic-Tyr 3 -octreotide. The patient-specific S values calculated by GATE Monte Carlo code and the corresponding S values obtained by MIRDOSE program differed within 4.3% on an average for self-irradiation, and differed within 69.6% on an average for cross-irradiation. However, the agreement between total organ doses calculated by GATE code and MIRDOSE program for all patients was reasonably well (percentage difference was about 4.6% on an average). Normal and tumor absorbed doses calculated with GATE were slightly higher than those calculated with MIRDOSE program. The average ratio of GATE absorbed doses to MIRDOSE was 1.07 ± 0.11 (ranging from 0.94 to 1.36). According to the results, it is proposed that when cross-organ irradiation is dominant, a comprehensive approach such as GATE Monte Carlo dosimetry be used since it provides more reliable dosimetric results. |
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