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. 2016 May-Aug;15(2):114-23.
doi: 10.4103/1450-1147.174700.

A 3D Monte Carlo Method for Estimation of Patient-specific Internal Organs Absorbed Dose for (99m)Tc-hynic-Tyr(3)-octreotide Imaging

Mehdi Momennezhad  1 , Shahrokh Nasseri  2 , Seyed Rasoul Zakavi  3 , Ali Asghar Parach  4 , Mahdi Ghorbani  1 , Ruhollah Ghahraman Asl  1
Affiliations

A 3D Monte Carlo Method for Estimation of Patient-specific Internal Organs Absorbed Dose for (99m)Tc-hynic-Tyr(3)-octreotide Imaging

Mehdi Momennezhad et al. World J Nucl Med. 2016 May-Aug.

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.

Keywords: GATE Monte Carlo package; MIRDOSE; S value; patient-specific dosimetry.

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Conflict of interest statement

Conflict of Interest: None declared.

Figures

Figure 1
Figure 1
Anterior and posterior whole-body planar images at approximately 1-2 h after administration. (a): Neuroendocrine lesions is not revealed (patient1) (b) Neuroendocrine tumor is in multiple foci in the liver (patient 2) (c) Neuroendocrine tumor is in small bowel (right periumbilical region) (patient 3) (d) Neuroendocrine tumor is in the pancreatic head with metastasis to the right shoulder, left orbit and skull (patient 4)
Figure 2
Figure 2
Decay time activity data for some of the normal organs of the four patients. The data were fitted with monoexponential function to find the effective decay constant
Figure 3
Figure 3
Ratio between GATE and MIRDOSE absorbed doses for the four patients. No tumor was visible in a single SPECT field of view for patient 1
Figure 4
Figure 4
Average percent contributions of self- and cross-organ irradiation for all normal organ and tumor doses. The data were calculated by GATE Monte Carlo code
Figure 5
Figure 5
Integrated dose volume histograms based on 3D dose distributions calculated with GATE Monte Carlo code for regions and tumors considered in this study for each patient separately. From these DVHs, based on the large interpatient dose variation in normal organs and tumors, the importance of patient-specific dosimetry can be considered
See this image and copyright information in PMC

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