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Jung, Seongmoon,Sung, Wonmo,Ye, Sung-Joon Dove Medical Press 2017 International journal of nanomedicine Vol.12 No.-
<P>This work aims to develop a Monte Carlo (MC) model for pinhole K-shell X-ray fluorescence (XRF) imaging of metal nanoparticles using polychromatic X-rays. The MC model consisted of two-dimensional (2D) position-sensitive detectors and fan-beam X-rays used to stimulate the emission of XRF photons from gadolinium (Gd) or gold (Au) nanoparticles. Four cylindrical columns containing different concentrations of nanoparticles ranging from 0.01% to 0.09% by weight (wt%) were placed in a 5 cm diameter cylindrical water phantom. The images of the columns had detectable contrast-to-noise ratios (CNRs) of 5.7 and 4.3 for 0.01 wt% Gd and for 0.03 wt% Au, respectively. Higher concentrations of nanoparticles yielded higher CNR. For 1×10<SUP>11</SUP> incident particles, the radiation dose to the phantom was 19.9 mGy for 110 kVp X-rays (Gd imaging) and 26.1 mGy for 140 kVp X-rays (Au imaging). The MC model of a pinhole XRF can acquire direct 2D slice images of the object without image reconstruction. The MC model demonstrated that the pinhole XRF imaging system could be a potential bioimaging modality for nanomedicine.</P>
Jung, Seongmoon,Sung, Wonmo,Lee, Jaegi,Ye, Sung-Joon Elsevier 2018 Nuclear instruments & methods in physics research. Vol.415 No.-
<P><B>Abstract</B></P> <P>Emerging radiological applications of gold nanoparticles demand low-energy electron/photon transport calculations including details of an atomic relaxation process. Recently, MCNP® version 6.1 (MCNP6.1) has been released with extended cross-sections for low-energy electron/photon, subshell photoelectric cross-sections, and more detailed atomic relaxation data than the previous versions. With this new feature, the atomic relaxation process of MCNP6.1 has not been fully tested yet with its new physics library (eprdata12) that is based on the Evaluated Atomic Data Library (EADL). In this study, MCNP6.1 was compared with GATEv7.2, PENELOPE2014, and EGSnrc that have been often used to simulate low-energy atomic relaxation processes. The simulations were performed to acquire both photon and electron spectra produced by interactions of 15 keV electrons or photons with a 10-nm-thick gold nano-slab. The photon-induced fluorescence X-rays from MCNP6.1 fairly agreed with those from GATEv7.2 and PENELOPE2014, while the electron-induced fluorescence X-rays of the four codes showed more or less discrepancies. A coincidence was observed in the photon-induced Auger electrons simulated by MCNP6.1 and GATEv7.2. A recent release of MCNP6.1 with eprdata12 can be used to simulate the photon-induced atomic relaxation.</P>
Jung, Seongmoon,Sung, Wonmo,Ye, Sung-Joon Elsevier 2018 Nuclear instruments & methods in physics research. Vol.430 No.-
<P><B>Abstract</B></P> <P>With emerging interests in subcellular and nano-scale energy deposition of low-energy electrons, new cross-sectional models for the low-energy electron transport have been integrated into recent releases of Monte Carlo (MC) codes. MCNP6.1 has been released which included extended cross-sections for low-energy electron interactions based on the Evaluated Electron Data Library (EEDL). Moreover, a single-event electron transport method was introduced down to 10 eV. In this study, MCNP6.1 has been benchmarked against early versions of PENELOPE2014 and Geant4-DNA by comparing dose-point kernels (DPKs) of electrons of 100 eV, 1 keV and 10 keV. In addition, radial dose distributions around a 2 or 15 nm-diameter gold nanoparticle (GNP) irradiated by 50 kVp X-rays were calculated for comparison. For all electron energies, the DPKs calculated by MCNP6.1 reached the maximum values at shorter distances and then were decreased more rapidly than those calculated by the other codes. Radial doses within 2 nm from the surface of the GNPs calculated by MCNP6.1 were 1.04 – 1.89 times and 1.13 – 1.58 times higher than those calculated by Geant4-DNA and PENELOPE2014, respectively. These differences would stem from the fact that inelastic cross-sections of MCNP6.1 for low-energy electrons are higher than those of the other codes. At this moment, it is difficult to judge which of the codes is more accurate for nano-scale dose calculations than the others. Depending on the geometrical configuration of the electron source (herein GNPs) and the target (e.g., DNA), the difference in the interaction data for low-energy electron transport, especially below 10 keV, would result in significant differences in calculation of radio-biological effects on the target. It can be concluded that one should pay attention to the interaction data as well as the transport parameters used for MC low-energy radiation transport in a nano- and micro-scale.</P>
Jung, Seongmoon,Kim, Bitbyeol,Kim, Jung-in,Park, Jong Min,Choi, Chang Heon The Korean Association for Radiation Protection 2020 방사선방어학회지 Vol.45 No.4
Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.
Evaluation of the microscopic dose enhancement for nanoparticle-enhanced Auger therapy
Sung, Wonmo,Jung, Seongmoon,Ye, Sung-Joon Institute of Physics in association with the Ameri 2016 Physics in medicine & biology Vol.61 No.21
<P>The aim of this study is to investigate the dosimetric characteristics of nanoparticle-enhanced Auger therapy. Monte Carlo (MC) simulations were performed to assess electron energy spectra and dose enhancement distributions around a nanoparticle. In the simulations, two types of nanoparticle structures were considered: nanoshell and nanosphere, both of which were assumed to be made of one of five elements (Fe, Ag, Gd, Au, and Pt) in various sizes (2–100 nm). Auger-electron emitting radionuclides (I-125, In-111, and Tc-99m) were simulated within a nanoshell or on the surface of a nanosphere. For the most promising combination of Au and I-125, the maximum dose enhancement was up to 1.3 and 3.6 for the nanoshell and the nanosphere, respectively. The dose enhancement regions were restricted within 20–100 nm and 0–30 nm distances from the surface of Au nanoshell and nanosphere, respectively. The dose enhancement distributions varied with sizes of nanoparticles, nano-elements, and radionuclides and thus should be carefully taken into account for biological modeling. If the nanoparticles are accumulated in close proximity to the biological target, this new type of treatment can deliver an enhanced microscopic dose to the target (e.g. DNA). Therefore, we conclude that Auger therapy combined with nanoparticles could have the potential to provide a better therapeutic effect than conventional Auger therapy alone.</P>