[en] Two dosimeters, positioned on the chest and back, could provide sufficient information for reasonable estimation of effective dose (E) for most exposure situations, excluding the possibility of significant underestimation of effective dose. Use of these two dosimeters with a suitable algorithm could not only solve the underestimation problem of the single-dosimeter approach, but could also alleviate the disadvantages of the multiple-dosimeter approach. However, it has not yet been confirmed experimentally whether the two-dosimeter approach estimates effective dose adequately or merely conservatively. Two-dosimeter algorithms were developed by simplified geometry and Monte Carlo simulations because it was not able to measure the effective dose directly. In this present study, the two-dosimeter approach was experimentally validated with a measurement system called pseudo Effective Dose Measurement System (EDMS) which is developed in the present study to measure effective dose. This system comprises 38 very small isotropic-responding high-sensitivity MOSFET dosimeters in an ATOM adult male phantom supported by 3D image-based Monte Carlo simulation technology to obtain accurate values of organ doses, effective dose and other quantities of interest. The EDMS is portable and very easy to use in the field and it measures the doses on a real-time basis. Because the ATOM adult male phantom has only 4 organs including bone, soft tissue, brain, and lungs, the other organs necessary for calculation of effective dose were defined with reference to the MIRD5 mathematical phantom. The numbers and locations of the MOSFET dosimeters were determined carefully after considering the tissue weighting factors, shapes and volumes of the organs. Each organ dose was determined by the 1-6 point-wise absorbed doses measured with the MOSFET dosimeters. The MOSFET dosimeter had been selected in the present study because it is very small and can measure radiation dose on a real-time basis. The MOSFET dosimeter, however, made mainly of silicon and epoxy, shows some energy dependence for low-energy photons. That is, when used in a phantom, it overestimates absorbed doses due to the existence of low-energy scattered photons. The MOSFET dosimeter shows some degree of angular dependence as well. Therefore, for accurate measurement of organ and tissue doses, the present study determined, by Monte Carlo simulations with the Monte Carlo N-Particle Transport Code System (MCNPX), the relative response (to tissue dose) of the MOSFET dosimeter, and thereby the dose correction factors, at various dosimeter locations in the ATOM adult male phantom. The MOSFET dosimeter is controlled by the MOSFET AutoSense^TM Dose Verification System and all messages generated by the system are recorded in 'MsgHistoryOnCOM.txt'. A data process program, which can read the text file and calculate organ doses, E and other dose quantities was developed in C++. The 2007 recommendation of International Commission on Radiological Protection (ICRP 103) uses organ-averaged doses, called equivalent doses, and tissue weighting factors to calculate effective dose. The recommendation also designated two ICRP reference phantoms to be used in calculation of equivalent doses and effective dose. However, the EDMS measures effective dose using an ATOM adult male phantom and 38 MOSFET dosimeters, which results in an approximate measurement of effective dose. Therefore, in the present study, the error of effective dose measurement was determined by Monte Carlo simulations using the ICRP reference phantoms and the ATOM-MIRD hybrid phantoms. The ATOMMIRD hybrid phantoms are developed in the present study by combining the CT images of the ATOM phantoms (for lungs, bone, brain, and skin) and the MIRD5 mathematical phantom (for the other organs). The effective dose calculated by the ICRP reference phantoms and the ATOM-MIRD hybrid phantoms showed good agreement for high energy photon beams (≥100 keV) for all irradiation geometries. The maximum difference was 35%, which occurs for the 30 keV photon beam in the anterior-posterior (AP) direction. In order to evaluate the performance of the two dosimeter approach, the EDMS was placed in several non-uniform radiation fields in nuclear power plants (NPPs) and the effective dose measured by the EDMS was compared with the estimated effective dose from the two-dosimeter algorithms. The results were very convincing; that is, the two-dosimeter approach neither significantly overestimates nor seriously underestimates the effective dose. The results confirm the previous Monte Carlo simulation results that the two-dosimeter approach can be used to determine effective dose without significant overestimation or underestimation

[en] Implementing effective dose in radiation protection is defined as a weighted average of organ doses to 23 organs and tissue in a human body. The effective dose has been measured, for some research purpose, by inserting hundreds of TLD chips to an anthropomorphic physical phantom of calculated by a Monte Carlo radiation transport simulation. However, both of these approaches are very complicated and cannot be used in the fields by practicing health physicists. A measurement system called Effective Dose Measurement System(EDMS) is being developed at Hanyang University. In this study, we verified EDMS effective dose methodology using Monte Carlo simulation and the preliminary measurement. First, this study investigated radiological characterization of the High-sensitivity MOSFET dosimeter using Monte Carlo simulation and experiment. Also, we decided Energy Dependence Correction Factor(EDCF) of each MOSFET dosimeter. This study developed Hybrid Voxel Anthropomorphic Phantom(HVAP) to calculate uncertainty of effective dose due to use of a limited number of dosimeters. The errors of EDMS effective dose methodology are not significant (less than a 6%) considering all photon energies and irradiation geometries in this study. Then, we measured prototype EDMS in radiation fields(C0-60 and Cs-137). The result of EDMS effective dose measurement compared with Monte Calro simulation of the MIRD-type mathematical phantom. Because the ATOM phantom was different from MIRD-type model used in the simulation, the differences in effective doses are within 13%. Also, the error of EDMS found to be about 10% adding up radiological characterization of the High-sensitivity MOSFET dosimeter, the errors of EDMS effective dose methodology and the errors of Energy Dependence Correction Factor. The results of this study will be used in order to EDMS development. We will develop the software for data acquisition and effective dose calculation

[en] In Korea, a real-time effective dose measurement system is in development. The system uses 32 high-sensitivity MOSFET dosimeters to measure radiation doses at various organ locations in an anthropomorphic physical phantom. The MOSFET dosimeters are, however, mainly made of silicon and shows some degree of energy and angular dependence especially for low energy photons. This study determines the correction factors to correct for these dependences of the MOSFET dosimeters for accurate measurement of radiation doses at organ locations in the phantom. For this, first, the dose correction factors of MOSFET dosimeters were determined for the energy spectrum in the steam generator channel of the Kori Nuclear Power Plant Unit no.1 by Monte Carlo simulations. Then, the results were compared with the dose correction factors from 0.662 MeV and 1.25 MeV mono-energetic photons. The difference of the dose correction factors were found very negligible (≤1.5%), which in general shows that the dose corrections factors determined from 0.662 MeV and 1.25 MeV can be in a steam general channel head of a nuclear power plant. The measured effective dose was generally found to decrease by ∼7% when we apply the dose correction factors

[en] The anthropomorphic computational phantoms are classified into two groups. One group is the stylized phantoms, or MIRD phantoms, which are based on mathematical representations of the anatomical structures. The shapes and positions of the organs and tissues in these phantoms can be adjusted by changing the coefficients of the equations in use. The other group is the voxel phantoms, which are based on tomographic images of a real person such as CT, MR and serially sectioned color slice images from a cadaver. Obviously, the voxel phantoms represent the anatomical structures of a human body much more realistically than the stylized phantoms. A realistic representation of anatomical structure is very important for an accurate calculation of radiation dose in the human body. Consequently, the ICRP recently has decided to use the voxel phantoms for the forthcoming update of the dose conversion coefficients. However, the voxel phantoms also have some limitations: (1) The topology and dimensions of the organs and tissues in a voxel model are extremely difficult to change, and (2) The thin organs, such as oral mucosa and skin, cannot be realistically modeled unless the voxel resolution is prohibitively high. Recently, a new approach has been implemented by several investigators. The investigators converted their voxel phantoms to hybrid computational phantoms based on NURBS (Non-Uniform Rational B-Splines) surface, which is smooth and deformable. It is claimed that these new phantoms have the flexibility of the stylized phantom along with the realistic representations of the anatomical structures. The topology and dimensions of the anatomical structures can be easily changed as necessary. Thin organs can be modeled without affecting computational speed or memory requirement. The hybrid phantoms can be also used for 4-D Monte Carlo simulations. In this preliminary study, the external shape of a voxel phantom (i.e., skin), HDRK-Man, was converted to a hybrid computational phantom by using the subdivision surfaces

[en] The close relationship between the proton dose distribution and the distribution of prompt gammas generated by proton-induced nuclear interactions along the path of protons in a water phantom was demonstrated by means of both Monte Carlo simulations and limited experiments. In order to test the clinical applicability of the method for determining the distal dose edge in a human body, a human voxel model, constructed based on a body-composition-approximated physical phantom, was used, after which the MCNPX code was used to analyze the energy spectra and the prompt gamma yields from the major elements composing the human voxel model; finally, the prompt gamma distribution, generated from the voxel model and measured by using an array-type prompt gamma detection system, was calculated and compared with the proton dose distribution. According to the results, effective prompt gammas were produced mainly by oxygen, and the specific energy of the prompt gammas, allowing for selective measurement, was found to be 4.44 MeV. The results also show that the distal dose edge in the human phantom, despite the heterogeneous composition and the complicated shape, can be determined by measuring the prompt gamma distribution with an array-type detection system.

[en] Recently a high-quality voxel model of a Korean adult male was constructed at Hanyang University by using very high resolution serially-sectioned anatomical images of a cadaver, which was provided by the Korean Institute of Science and Technology Information (KISTI). Most existing voxel phantoms are developed based on an individual in the supine posture. This study converted the HDRK-Man voxel model into surface model and adjusted the flattened back of the HDRK-Man to a normal shape in the upright posture using 3D graphic software such as 3D-DOCTOR^TM, Rapidform 2006, Rhinoceros 4.0, MAYA 8.5. The effective doses of adjusted model were compared with those of unadjusted model for some standard irradiation geometries (i.e., AP, PA, LLAT, RLAT). In general, the differences were not very large and, among those, the largest difference was found for the PA radiation geometry, as expected. These methodologies can be used for the development of various deformed posture models of HDRK-Man in the later stage of this project

[en] In recent years, the MOSFET dosimeter has been widely used in various medical applications such as dose verification in radiation therapeutic and diagnostic applications. The MOSFET dosimeter is, however, mainly made of silicon and shows some energy dependence for low energy photons. Therefore, the MOSFET dosimeter tends to overestimate the dose for low energy scattered photons in a phantom. This study determines the correction factors to compensate these dependences of the MOSFET dosimeter in ATOM phantom. For this, we first constructed a computational model of the ATOM phantom based on the 3D CT image data of the phantom. The voxel phantom was then implemented in a Monte Carlo simulation code and used to calculate the energy spectrum of the photon field at each of the MOSFET dosimeter locations in the phantom. Finally, the correction factors were calculated based on the energy spectrum of the photon field at the dosimeter locations and the pre-determined energy and directional dependence of the MOSFET dosimeter. Our result for ⁶⁰Co and ¹³⁷Cs photon fields shows that the correction factors are distributed within the range of 0.89 and 0.97 considering all the MOSFET dosimeter locations in the phantom

[en] This study aimed to evaluate the initial outcomes of proton beam therapy (PBT) for hepatocellular carcinoma (HCC) in terms of tumor response and safety. HCC patients who were not indicated for standard curative local modalities and who were treated with PBT at Samsung Medical Center from January 2016 to February 2017 were enrolled. Toxicity was scored using the Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Tumor response was evaluated using modified Response Evaluation Criteria in Solid Tumors (mRECIST). A total of 101 HCC patients treated with PBT were included. Patients were treated with an equivalent dose of 62–92 GyE10. Liver function status was not significantly affected after PBT. Greater than 80% of patients had Child-Pugh class A and albumin-bilirubin (ALBI) grade 1 up to 3-months after PBT. Of 78 patients followed for three months after PBT, infield complete and partial responses were achieved in 54 (69.2%) and 14 (17.9%) patients, respectively. PBT treatment of HCC patients showed a favorable infield complete response rate of 69.2% with acceptable acute toxicity. An additional follow-up study of these patients will be conducted

[en] Effective dose is very important dose quantities in radiation protection. It is determined as a weighted average of organ doses to 28 organs and tissues in a human body. Effective dose has been measured by some researchers by inserting hundreds of TLD chips into a RANDO phantom, which is however too complicated and time consuming to be used by a practicing health physicist in the fields. To this end, the present study developed a measurement system, called EDMS (Effective Dose Measurement System), which can quickly measure effective dose in the fields

[en] Many different voxel models, developed using tomographic images of human body, are used in various fields including both ionizing and non-ionizing radiation fields. Recently a high-quality voxel model/ named HDRK-Man, was constructed at Hanyang University and used to calculate the dose conversion coefficients (DCC) values for external photon and neutron beams using the MCNPX Monte Carlo code. The objective of the present study is to set up the HDRK-Man model in Geant4 in order to use it in more advanced calculations such as 4-D Monte Carlo simulations and space dosimetry studies involving very high energy particles. To that end, the HDRK-Man was ported to Geant4 and used to calculate the DCC values for external photon beams. The calculated values were then compared with the results of the MCNPX code. In addition, a computational Linux cluster was built to improve the computing speed in Geant4