Validation of the Monte Carlo simulator GATE for indium-111 imaging

The specific absorbed fraction (SAF) of energy is an essential element of internal dose assessment. Here reported a set of SAFs calculated for selected organs of a human voxel-based phantom. The Monte Carlo transport code GATE version 6.1 was used to simulate monoenergetic photons and electrons with energies ranging from 10 keV to 2 MeV. The particles were emitted from three source organs: kidneys, liver, and spleen. SAFs were calculated for three target regions in the body (kidneys, liver, and spleen) and compared with the results obtained using the MCNP4B and GATE/GEANT4 Monte Carlo codes. For most photon energies, the self-irradiation is higher, and the cross-irradiation is lower in the GATE results compared to the MCNP4B. The results show generally good agreement for photons and high-energy electrons with discrepancies within − 2% ±3%. Nevertheless, significant differences were found for cross-irradiation of photons of lower energy and electrons of higher energy due to statistical uncertainties larger than 10%. The comparisons of the SAF values for the human voxel phantom do not show significant differences, and the results also demonstrated the usefulness and applicability of GATE Monte Carlo package for voxel level dose calculations in nonuniform media. The present SAFs calculation for the Zubal voxel phantom is validated by the intercomparison of the results obtained by other Monte Carlo codes.

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“…However, the uses of the GATE and GEANT4 have been evaluated for dosimetry applications at previous publications. [456]…”

Section: Methodsmentioning

confidence: 99%

Specific absorbed fractions of internal photon and electron emitters in a human voxel-based phantom: A monte carlo study

et al. 2017

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“…GATE has been validated extensively by measurements with various isotopes and collimators [19][20][21]. Additionally for this study, simulations were performed wherein the parameters mimicked the measurements described hereafter, thereby, including all detector parts as well as the phantom table.…”

Section: Validation Of Monte Carlo Simulatormentioning

confidence: 99%

Degradation of myocardial perfusion SPECT images caused by contaminants in thallous (201Tl) chloride

Staelens

Wit

Lemahieu

et al. 2008

Eur J Nucl Med Mol Imaging

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Purpose Thallous ( 201 Tl) chloride is a single-photon emission computed tomography (SPECT) tracer mainly used for assessing perfusion and viability of myocardial tissue. 201 Tl emits X-rays around 72 keV and gammas at 167 keV, and has a half-life of 73 h. Regulations allow an intrinsic contamination up to 3-5%, which is mainly caused by 200 Tl (368 keV; 26 h) and by 202 Tl (439 keV; 12.2 days). Contraintuitive to the low-level percentages in which these contaminants are present, their impact may be significant because of much higher gamma camera sensitivity for these high-energy photon emissions. Therefore, we investigate the effects of the contaminants in terms of detected fractions of photons in projections and contrast degradation in reconstructed images. Methods Acquisitions of a digital thorax phantom filled with thallous ( 201 Tl) chloride were simulated with a validated Monte Carlo tool, thereby, modelling 1% of contamination by 200 Tl and 202 Tl each. In addition, measurements of a thorax phantom on a dual-headed gamma camera were performed. The product used was contaminated by 0.17% of 200 Tl and 0.24% of 202 Tl at activity reference time (ART). This ART is specified by the manufacturer, thereby, accounting for the difference in halflives of 201 Tl and its contaminants. These measurements were repeated at different dates associated with various contamination levels. Results Simulations showed that, with 1% of 200 Tl and 202 Tl, the total contamination in the 72 keV window can rise up to one out of three detected photons. For the 167keV window, the contamination is even more pronounced: more than four out of five detections in this photopeak window originate from contaminants. Measurements indicate that cold lesion contrast in myocardial perfusion SPECT imaging is at maximum close to ART. In addition to a higher noise level, relative contrast decreases 15% 2 days early to ART, which is explained by an increase in 200 Tl contamination. After ART, contrast decreased by 16% when the 202 Tl contamination increased to the maximal allowed limit. Conclusions Contra-intuitive to the low-level percentages in which they are typically present, penetration and downscatter of high-energy photons from 200 Tl and 202 Tl significantly contribute to thallous ( 201 Tl) chloride images, thereby, reducing contrast and adding noise. These findings may prompt for improved production methods, for updated policies with regard to timing of usage, and they also render the usefulness of adding the high photopeak window (167 Eur J Nucl Med Mol Imaging (2008)

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“…This is true only for low-energy isotopes, such as Tc-99m, when considering photons in the conventional 20% energy window. However, such a model is not appropriate for isotopes presenting high-energy emission, such as In-111 [20]. For high energy isotopes, Monte Carlo transportation of photons in the collimator can still be avoided by using pre-calculated angular response functions [21].…”

Section: Increasing the Throughput Of The Simulationsmentioning

confidence: 99%