Carlo Particle Transport Simulation Code Research Articles

Rare-Earth Oxides as Alternative High-Energy Photon Protective Fillers in HDPE Composites: Theoretical Aspects.

This work theoretically determined the high-energy photon shielding properties of high-density polyethylene (HDPE) composites containing rare-earth oxides, namely samarium oxide (Sm2O3), europium oxide (Eu2O3), and gadolinium oxide (Gd2O3), for potential use as lead-free X-ray-shielding and gamma-shielding materials using the XCOM software package. The considered properties were the mass attenuation coefficient (µm), linear attenuation coefficient (µ), half value layer (HVL), and lead equivalence (Pbeq) that were investigated at varying photon energies (0.001–5 MeV) and filler contents (0–60 wt.%). The results were in good agreement (less than 2% differences) with other available programs (Phy-X/PSD) and Monte Carlo particle transport simulation code, namely PHITS, which showed that the overall high-energy photon shielding abilities of the composites considerably increased with increasing rare-earth oxide contents but reduced with increasing photon energies. In particular, the Gd2O3/HDPE composites had the highest µm values at photon energies of 0.1, 0.5, and 5 MeV, due to having the highest atomic number (Z). Furthermore, the Pbeq determination of the composites within the X-ray energy ranges indicated that the 10 mm thick samples with filler contents of 40 wt.% and 50 wt.% had Pbeq values greater than the minimum requirements for shielding materials used in general diagnostic X-ray rooms and computerized tomography rooms, which required Pbeq values of at least 1.0 and 1.5 mmPb, respectively. In addition, the comparisons of µm, µ, and HVL among the rare-earth oxide/HDPE composites investigated in this work and other lead-free X-ray shielding composites revealed that the materials developed in this work exhibited comparable X-ray shielding properties in comparison with that of the latter, implying great potential to be used as effective X-ray shielding materials in actual applications.

Observation of morphological abnormalities in silkworm pupae after feeding 137CsCl-supplemented diet to evaluate the effects of low dose-rate exposure

Since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, morphological abnormalities in lepidopteran insects, such as shrinkage and/or aberration of wings, have been reported. Butterflies experimentally exposed to radiocesium also show such abnormalities. However, because of a lack of data on absorbed dose and dose–effect relationship, it is unclear whether these abnormalities are caused directly by radiation. We conducted a low dose-rate exposure experiment in silkworms reared from egg to fully developed larvae on a 137CsCl-supplemented artificial diet and estimated the absorbed dose to evaluate morphological abnormalities in pupal wings. We used 137CsCl at 1.3 × 103 Bq/g fresh weight to simulate 137Cs contamination around the FDNPP. Absorbed doses were estimated using a glass rod dosimeter and Monte Carlo particle transport simulation code PHITS. Average external absorbed doses were approximately 0.24 (on diet) and 0.016 mGy/day (near diet); the average internal absorbed dose was approximately 0.82 mGy/day. Pupal wing structure is sensitive to radiation exposure. However, no significant differences were observed in the wing-to-whole body ratio of pupae between the 137CsCl-exposure and control groups. These results suggest that silkworms are insensitive to low dose-rate exposure due to chronic ingestion of high 137Cs at a high concentration.

Utilization of Monte Carlo Particle Transport Simulation Code on Radiation Emergency Medicine at Hirosaki University

Utilization of Monte Carlo Particle Transport Simulation Code on Radiation Emergency Medicine at Hirosaki University

Maximum-likelihood estimation of scatter components algorithm for x-ray coherent scatter computed tomography of the breast

Coherent scatter computed tomography (CSCT) is a reconstructive x-ray imaging technique that yields the spatially resolved coherent-scatter cross section of the investigated object revealing structural information of tissue under investigation. In the original CSCT proposals the reconstruction of images from coherently scattered x-rays is done at each scattering angle separately using analytic reconstruction. In this work we develop a maximum likelihood estimation of scatter components algorithm (ML-ESCA) that iteratively reconstructs images using a few material component basis functions from coherent scatter projection data. The proposed algorithm combines the measured scatter data at different angles into one reconstruction equation with only a few component images. Also, it accounts for data acquisition statistics and physics, modeling effects such as polychromatic energy spectrum and detector response function. We test the algorithm with simulated projection data obtained with a pencil beam setup using a new version of MC-GPU code, a Graphical Processing Unit version of PENELOPE Monte Carlo particle transport simulation code, that incorporates an improved model of x-ray coherent scattering using experimentally measured molecular interference functions. The results obtained for breast imaging phantoms using adipose and glandular tissue cross sections show that the new algorithm can separate imaging data into basic adipose and water components at radiation doses comparable with Breast Computed Tomography. Simulation results also show the potential for imaging microcalcifications. Overall, the component images obtained with ML-ESCA algorithm have a less noisy appearance than the images obtained with the conventional filtered back projection algorithm for each individual scattering angle. An optimization study for x-ray energy range selection for breast CSCT is also presented.

Overview of the PHITS code and its application to medical physics

Particle and Heavy Ion Transport code System, PHITS, is a general purpose three-dimensional Monte Carlo particle transport simulation code developed through collaboration with several institutes in Japan and Europe. To apply PHITS to medical physics, two special functions were implemented in the code: an event generator mode and a microdosimetric tally function. Utilizing these functions, a new relative-biological-effectiveness -weighted dose estimation method for charged-particle therapy was established on the basis of the double-stochastic microdosimetric kinetic model. Owing to these features, PHITS has been used for various medical applications, such as patient dose estimation for radiotherapy and computed tomography examination.

Parallelization of a Monte Carlo particle transport simulation code

We have developed a high performance version of the Monte Carlo particle transport simulation code MC4. The original application code, developed in Visual Basic for Applications (VBA) for Microsoft Excel, was first rewritten in the C programming language for improving code portability. Several pseudo-random number generators have been also integrated and studied. The new MC4 version was then parallelized for shared and distributed-memory multiprocessor systems using the Message Passing Interface. Two parallel pseudo-random number generator libraries (SPRNG and DCMT) have been seamlessly integrated. The performance speedup of parallel MC4 has been studied on a variety of parallel computing architectures including an Intel Xeon server with 4 dual-core processors, a Sun cluster consisting of 16 nodes of 2 dual-core AMD Opteron processors and a 200 dual-processor HP cluster. For large problem size, which is limited only by the physical memory of the multiprocessor server, the speedup results are almost linear on all systems. We have validated the parallel implementation against the serial VBA and C implementations using the same random number generator. Our experimental results on the transport and energy loss of electrons in a water medium show that the serial and parallel codes are equivalent in accuracy. The present improvements allow for studying of higher particle energies with the use of more accurate physical models, and improve statistics as more particles tracks can be simulated in low response time.

MedLinac2: a GEANT4 based software package for radiotherapy.

Dose distribution evaluation in oncological radiotherapy treatments is an outstanding problem that requires sophisticated computing technologies to optimize the clinical results (i.e. increase the dose to the tumour and reduce the dose to the healthy tissues). Nowdays, dose calculation algorithms based on the Monte Carlo method are generally regarded as the most accurate tools for radiotherapy. The flexibility of the GEANT4 (GEometry ANd Tracking) Monte Carlo particle transport simulation code allows a wide range of applications, from high-energy to medical physics. In order to disseminate and encourage the use of Monte Carlo method in oncological radiotherapy, a software package based on the GEANT4 Monte Carlo toolkit has been developed. The developed package (MedLinac2) allows to simulate in an adequate flexible way a linear accelerator for radiotherapy and to evaluate the dose distributions.

Development of a Reference Korean Voxel Model by Adjusting the Size of the Organs and Tissues

The objective of this study was to adjust the height, weight, and organ and tissue sizes of a Korean voxel model in order to construct a Reference Korean voxel model. The adjustment of the height and skeletal mass was achieved by scaling the voxel dimensions. The sizes of the organs and tissues were adjusted to the Reference Korean data by adding or removing voxels on the surface. The adjusted voxel model is 171 cm in height, 68 kg in weight, which exactly matches the Reference Korean data. The size of the voxels (= voxel resolution) is 1.981 mm × 1.981 mm × 2.0854 mm. The organ and tissue masses of the adjusted model also are in a good agreement with the Reference Korean data; the differences are less than 7% for most of the organs and tissues. The unadjusted and adjusted voxel models were ported to the MCNPX Monte Carlo particle transport simulation code to calculate the equivalent doses to the organs and tissues and the effective doses. The calculated values were then compared in order to quantify the effect of the adjustment.

ATOM-MIRD Hybrid Voxel Model for Monte Carlo Calculations of Organ Doses: A Complement to a Physical Phantom

In this study, a hybrid voxel model was constructed by combining the voxel model of the ATOM adult male phantom with the organ models of the MIRD5 mathematical phantom. The organ models of the mathematical phantom were successfully transferred to the hybrid model, replicating the sizes of the organs within a 3% difference. Consequently, a total of 14 main radiosensitive organs were defined in the hybrid model. The developed model was implemented into a Monte Carlo particle transport simulation code, MCNPX, and used to calculate the organ doses, which were then compared with the TLD measured values.

Construction of a High-quality Voxel Model VKH-Man Using Serially Sectioned Images from Visible Korean Human Project in Korea

In this study, a high-quality voxel model of a Korean adult male was constructed using the Visible Korean Human (VKH) project’s serially sectioned anatomical images. The VKH images are transverse color photographs obtained from the serial sectioning of an adult Korean male cadaver (164 cm, 55 kg) at 0.2 mm intervals. A total of 28 organs and tissues were segmented with the color photographic images. The height and weight of the constructed voxel model, VKH-Man, is 164 cm and 59.6 kg, respectively. The voxel resolution of the model is 1.875 mm × 1.875 mm × 2 mm. The developed model was implemented into a Monte Carlo particle transport simulation code, MCNPX, to calculate the organ and tissue doses and, thereby, the effective doses, and the calculated values were compared with the values obtained from other computational models (KTMAN-2, VIP-Man, and ICRP-74).

Determination of distal dose edge location by measuring right-angled prompt-gamma rays from a 38 MeV proton beam

In clinical applications, it is very important to accurately determine the range of a proton beam in a patient. Recently, a prototype prompt-gamma scanning system, called a prompt-gamma scanner (PGS), has been constructed at Hanyang University in Korea with the collaboration of the Korean national cancer center (NCC), based on a series of Monte Carlo simulations. The PGS system is composed of a prompt-gamma collimator, a CsI(Tl) scintillation detector, a multi-channel analyzer (MCA), a precision movement system, and an integrated readout system. The prompt-gamma collimator is designed to effectively shield high-energy neutrons from the proton beam passage and subsequent capture gammas. The PGS system can be used to scan the distribution of the prompt gammas in the patient from the proton beam passage. The distribution of the prompt gammas can then be used to determine the proton beam range or the distal dose edge in the patient. In this study, the PGS system was tested with a 38 MeV proton beam at the Korea cancer center hospital (KCCH). The experiment was also simulated, using a Monte Carlo particle transport simulation code, MCNPX. Our result is very encouraging, showing that there is a clear correlation between the distribution of the prompt gammas and the location of the distal dose edge for the 38 MeV proton beam. According to our result, we believe that the location of the distal dose edge can be determined within 1–2 mm from the distribution of the prompt gammas.