title: A 3D Monte Carlo Method for Estimation of Patient-specific Internal Organs Absorbed Dose for (99m)Tc-hynic-Tyr(3)-octreotide Imaging.
abstract: 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.
authors.affiliation: Department of Medical Physics, Faculty of Medicine, University of Medical Sciences, Mashhad, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Momennezhad
authors.affiliation: Department of Medical Physics, Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Shahrokh
authors.initials: S
authors.lastname: Nasseri
authors.affiliation: Department of Nuclear Medicine, Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Seyed Rasoul
authors.initials: SR
authors.lastname: Zakavi
authors.affiliation: Department of Medical Physics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
authors.forename: Ali Asghar
authors.initials: AA
authors.lastname: Parach
authors.affiliation: Department of Medical Physics, Faculty of Medicine, University of Medical Sciences, Mashhad, Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Ghorbani
authors.affiliation: Department of Medical Physics, Faculty of Medicine, University of Medical Sciences, Mashhad, Iran.
authors.forename: Ruhollah Ghahraman
authors.initials: RG
authors.lastname: Asl
keywords: GATE Monte Carlo package; MIRDOSE; S value; patient-specific dosimetry