• Nuclear Engineering and Technology
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• v.38 no.3
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• pp.239-250
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• 2006

Computational anthropomorphic phantoms are computer models of human anatomy used in the calculation of radiation dose distribution in the human body upon exposure to a radiation source. Depending on the manner to represent human anatomy, they are categorized into two classes: stylized and tomographic phantoms. Stylized phantoms, which have mainly been developed at the Oak Ridge National Laboratory (ORNL), describe human anatomy by using simple mathematical equations of analytical geometry. Several improved stylized phantoms such as male and female adults, pediatric series, and enhanced organ models have been developed following the first hermaphrodite adult stylized phantom, Medical Internal Radiation Dose (MIRD)-5 phantom. Although stylized phantoms have significantly contributed to dosimetry calculation, they provide only approximations of the true anatomical features of the human body and the resulting organ dose distribution. An alternative class of computational phantom, the tomographic phantom, is based upon three-dimensional imaging techniques such as magnetic resonance (MR) imaging and computed tomography (CT). The tomographic phantoms represent the human anatomy with a large number of voxels that are assigned tissue type and organ identity. To date, a total of around 30 tomographic phantoms including male and female adults, pediatric phantoms, and even a pregnant female, have been developed and utilized for realistic radiation dosimetry calculation. They are based on MRI/CT images or sectional color photos from patients, volunteers or cadavers. Several investigators have compared tomographic phantoms with stylized phantoms, and demonstrated the superiority of tomographic phantoms in terms of realistic anatomy and dosimetry calculation. This paper summarizes the history and current status of both stylized and tomographic phantoms, including Korean computational phantoms. Advantages, limitations, and future prospects are also discussed.

• Journal of radiological science and technology
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• v.43 no.6
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• pp.443-451
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• 2020

This study is to evaluate absorbed dose from right lung for brachytherapy and to estimate the effects of tissue heterogeneities on dose distribution for Iridium-192 source using Monte Carlo simulation. The study employed Geant4 code as Monte Carlo simulation to calculate the dosimetry parameters. The dose distribution of Iridium-192 source in solid water equivalent phantom including aluminium plate or steel plate inserted was calculated and compared with the measured dose by the ion chamber at various distances. And the simulation was used to evaluate the dose of gamma radiation absorbed in the lung organ and other organs around it. The dose distribution embedded in right lung was calculated due to the presence of heart, thymus, spine, stomach as well as left lung. The geometry of the human body was made up of adult male MIRD type of the computational human phantom. The dosimetric characteristics obtained for aluminium plate inserted were in good agreement with experimental results within 4%. The simulation results of steel plate inserted agreed well with a maximum difference 2.75%. Target organ considered to receive a dose of 100%, the surrounding organs were left the left lung of 3.93%, heart of 10.04%, thymus of 11.19%, spine of 12.64% and stomach of 0.95%. When the statistical error is performed for the computational human phantom, the statistical error of value is under 1%.

• Journal of Radiation Protection and Research
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• v.47 no.3
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• pp.111-133
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• 2022

The exciting advancement related to the "modeling of digital human" in terms of a computational phantom for radiation dose calculations has to do with the latest hype related to deep learning. The advent of deep learning or artificial intelligence (AI) technology involving convolutional neural networks has brought an unprecedented level of innovation to the field of organ segmentation. In addition, graphics processing units (GPUs) are utilized as boosters for both real-time Monte Carlo simulations and AI-based image segmentation applications. These advancements provide the feasibility of creating three-dimensional (3D) geometric details of the human anatomy from tomographic imaging and performing Monte Carlo radiation transport simulations using increasingly fast and inexpensive computers. This review first introduces the history of three types of computational human phantoms: stylized medical internal radiation dosimetry (MIRD) phantoms, voxelized tomographic phantoms, and boundary representation (BREP) deformable phantoms. Then, the development of a person-specific phantom is demonstrated by introducing AI-based organ autosegmentation technology. Next, a new development in GPU-based Monte Carlo radiation dose calculations is introduced. Examples of applying computational phantoms and a new Monte Carlo code named ARCHER (Accelerated Radiation-transport Computations in Heterogeneous EnviRonments) to problems in radiation protection, imaging, and radiotherapy are presented from research projects performed by students at the Rensselaer Polytechnic Institute (RPI) and University of Science and Technology of China (USTC). Finally, this review discusses challenges and future research opportunities. We found that, owing to the latest computer hardware and AI technology, computational human body models are moving closer to real human anatomy structures for accurate radiation dose calculations.

• Progress in Medical Physics
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• v.33 no.4
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• pp.172-179
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• 2022

Recently, tetrahedral phantoms have been newly adopted as international standard mesh-type reference computational phantoms (MRCPs) by the International Commission on Radiological Protection, and a program has been developed to convert them to computational tomography images and DICOM-RT structure files for application of radiotherapy. Through this program, the use of the tetrahedral standard phantom has become available in clinical practice, but utilization has been difficult due to various library dependencies requiring a lot of time and effort for installation. To overcome this limitation, in this study a newly developed TET2DICOM-GUI, a TET2DICOM program based on a graphical user interface (GUI), was programmed using only the MATLAB language so that it can be used without additional library installation and configuration. The program runs in the same order as TET2DICOM and has been optimized to run on a personal computer in a GUI environment. A tetrahedron-based male international standard human phantom, MRCP-AM, was used to evaluate TET2DICOM-GUI. Conversion into a DICOM-RT dataset applicable in clinical practice in about one hour with a personal computer as a basis was confirmed. Also, the generated DICOM-RT dataset was confirmed to be effectively implemented in the radiotherapy planning system. The program developed in this study is expected to replace actual patient data in future studies.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.295-303
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• 2023

Whole-body counters are widely used to assess internal contamination after a nuclear accident. However, it is difficult to determine radioiodine activity due to limitations in conventional calibration phantoms. Inhaled or ingested radioiodine is heterogeneously distributed in the human body, necessitating time-dependent biodistribution for the assessment of the internal contamination caused by the radioiodine intake. This study aims at calculating counting efficiencies considering the biodistribution of ¹³¹I in whole-body counting measurement. Monte Carlo simulations with computational human phantoms were performed to calculate the whole-body counting efficiency for a realistic radioiodine distribution after its intake. The biodistributions of ¹³¹I for different age groups were computed based on biokinetic models and applied to age- and gender-specific computational phantoms to estimate counting efficiency. After calculating the whole-body counting efficiencies, the efficiency correction factors were derived as the ratio of the counting efficiencies obtained by considering a heterogeneous biodistribution of ¹³¹I over time to those obtained using the BOMAB phantom assuming a homogeneous distribution. Based on the correction factors, the internal contamination caused by ¹³¹I can be assessed using whole-body counters. These correction factors can minimize the influence of the biodistribution of ¹³¹I in whole-body counting measurement and improve the accuracy of internal dose assessment.

• Progress in Medical Physics
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• v.23 no.3
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• pp.199-208
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• 2012

The computational human phantom including major radiation sensitive organs at risk (OARs) can be used in the field of radiotherapy, such as the variation of secondary cancer risks caused by the radiation therapy and the effective dose evaluation in diagnostic radiology. The present study developed a Korean adult female voxel phantom, VKH-Woman, based on serially sectioned color slice images of Korean female cadaver. The height and weight of the developed female voxel phantom are 160 cm and 52.72 kg, respectively that are virtually close to those of reference Korean female (161 cm and 54 kg). The female phantom consists of a total of 39 organs, including 27 organs recommended in the ICRP 103 publication for the effective dose calculations. The female phantom composes of $261{\times}109{\times}825$ voxels (=23,470,425 voxels) and the voxel resolution is $1.976{\times}1.976{\times}2.0619mm^3$ in the x, y, and z directions. The VHK-Woman is provided as both ASCII and Binary data formats to be conveniently implemented in Monte Carlo codes.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.1
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• pp.59-67
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• 2009

In this paper, we have proposed the structure of the IMADF(improved modified multiplication-free adaptive filter) to cancel the adaptive noise in biomedical signals. The IMADF structure use the one-step predicted filter in the multiplication-free adaptive digital filter(MADF) structure using the DPCM and Sign algorithm. And then we use the heart phantom model based on the magnetocardiographic (MCG) to test the biomedical signals and analyze the signal of it. Their functions of the heart phantom occur from the multidipole current source. This can play role the same in the real function of the human heart to study it. In the experimental results, the IMADF algorithm has reduced the computational complexity by use of only the addition operation without a multiplier. Also, under the condition of identical stationary-state error, it could obtain the stabled convergence characteristics that the IMADF algorithm is almost same as the sign algorithm, but is better than the MADF algorithm. Here, this algorithm has effective characteristics when the correlation of the input signal is highly.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.472-478
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• 2015

The patient dose incurred from diagnostic procedures during advanced radiotherapy has become an important issue. Many researchers in medical physics are using computational simulations to calculate complex parameters in experiments. However, extended computation times make it difficult for personal computers to run the conventional Monte Carlo method to simulate radiological images with high-flux photons such as images produced by computed tomography (CT). To minimize the computation time without degrading imaging quality, we applied a deterministic adaptation to the Monte Carlo calculation and verified its effectiveness by simulating CT image reconstruction for an image evaluation phantom (Catphan; Phantom Laboratory, New York NY, USA) and a human-like voxel phantom (KTMAN-2) (Los Alamos National Laboratory, Los Alamos, NM, USA). For the deterministic adaptation, the relationship between iteration numbers and the simulations was estimated and the option to simulate scattered radiation was evaluated. The processing times of simulations using the adaptive method were at least 500 times faster than those using a conventional statistical process. In addition, compared with the conventional statistical method, the adaptive method provided images that were more similar to the experimental images, which proved that the adaptive method was highly effective for a simulation that requires a large number of iterations-assuming no radiation scattering in the vicinity of detectors minimized artifacts in the reconstructed image.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2599-2605
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• 2022

The Korea Retrospective Dosimetry network (KREDOS) performed an inter-laboratory comparison to confirm the harmonization and reliability of the results of retrospective dosimetry using mobile phone. The mobile phones were exposed to ¹⁹²Ir while attached to the human phantoms in the field experiment, and the exposure doses read by each laboratory were compared. This paper describes the reference dosimetry performed to present the reference values for inter-comparison and to obtain additional information about the dose distribution. Reference dosimetry included both measurement using LiF:Mg,Cu,Si and calculation via MCNP simulation to allow a comparison of doses obtained with the two different methodologies. When irradiating the phones, LiF elements were attached to the phones and phantoms and irradiated at the same time. The comparison results for the front of the phantoms were in good agreement, with an average relative difference of about 10%, while an average of about 16% relative difference occurred for the back and side of the phantom. The differences were attributed to the different characteristics of the physical and simulated phantoms, such as anatomical structure and constituent materials. Nevertheless, there was about 4% of under-estimation compared to measurements in the overall linear fitting, indicating the calculations were well matched to the measurements.

• Investigative Magnetic Resonance Imaging
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• v.23 no.1
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• pp.38-45
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• 2019

Purpose: To demonstrate the high-resolution numerical simulation of the respiration-induced dynamic $B_0$ shift in the head using generalized susceptibility voxel convolution (gSVC). Materials and Methods: Previous dynamic $B_0$ simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based $B_0$ calculation methods. Here, we show that a recently-proposed gSVC method can simulate dynamic $B_0$ maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated $B_0$ maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. Results: The simulation predicted a maximum temporal variation of the $B_0$ shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced $B_0$ gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. Conclusion: We have presented an efficient simulation framework for respiration-induced $B_0$ variation in the head. The method can be used to predict $B_0$ shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic $B_0$ compensation strategies.