Heavy Ion Transport Code System Research Articles

Development of DynamicMC for PHITS Monte Carlo package.

Previously, we have developed DynamicMC for modeling relative movement of Oak Ridge National Laboratory phantom in a radiation field for the Monte Carlo N-Particle package (Health Physics. 2023,124(4):301-309). Using this software, three-dimensional dose distributions in a phantom irradiated by a certain mono-energetic (Mono E) source can be deduced through its graphical user interface. In this study, we extended DynamicMC to be used in combination with the Particle and Heavy Ion Transport code System (PHITS) by providing it with a higher flexibility for dynamic movement for an anthropomorphic phantom. For this purpose, we implemented four new functions into the software, which are (1) to generate not only Mono E sources but also those having an energy spectrum of an arbitrary radioisotope (2) to calculate the absorbed doses for several radiologically important organs (3) to automatically average the calculated absorbed doses along the path of the phantom and (4) to generate user-defined slab shielding materials. The first and third items utilize the PHITS-specific modalities named radioisotope-source and sumtally functions, respectively. The computational cost and complexity can be dramatically reduced with these features. We anticipate that the present work and the developed open-source tools will be in the interest of nuclear radiation physics community for research and teaching purposes.

Radiation attenuation and elemental composition of locally available ceramic tiles as potential radiation shielding materials for diagnostic X-ray rooms

Ceramic materials are being explored as alternatives to toxic lead sheets for radiation shielding due to their favorable properties like durability, thermal stability, and aesthetic appeal. However, crafting effective ceramics for radiation shielding entails complex processes, raising production costs. To investigate local viability, this study evaluated Malaysian ceramic tiles for shielding in diagnostic X-ray rooms. Different ceramics in terms of density and thickness were selected from local manufacturers. Energy Dispersive X-ray Fluorescence (EDXRF) and X-ray Fluorescence (XRF) characterized ceramic compositions, while Monte Carlo Particle and Heavy Ion Transport code System (MC PHITS) simulations determined Linear Attenuation Coefficient (LAC), Half-value Layer (HVL), Mass Attenuation Coefficient (MAC), and Mean Free Path (MFP) within the 40–150 kV energy range. Comparative analysis between MC PHITS simulations and real setups was conducted. The C3–S9 ceramic sample, known for homogeneous full-color structure, showcased superior shielding attributes, attributed to its high density and iron content. Notably, energy levels considerably impacted radiation penetration. Overall, C3–S9 demonstrated strong shielding performance, underlining Malaysia's potential ceramic tile resources for X-ray room radiation shielding.

Dose and irradiation time analysis of negative pi-meson therapy using particle and heavy ion transport code system (PHITS)

Dose and irradiation time analysis of negative pi-meson therapy using particle and heavy ion transport code system (PHITS)

Development of an electron track-structure mode for arbitrary semiconductor materials in PHITS

Abstract Optimizing the design of semiconductor detector requires an electron track-structure code that can trace an incident electron motion with energies down to a few eV and simulate the production process of excited electrons in semiconductors. We therefore developed an Electron Track Structure mode applicable to ARbitrary Targets (ETSART) and implemented it into Particle and Heavy Ion Transport code System (PHITS). ETSART can simulate the electrons’ motion in arbitrary semiconductor materials using their bandgap energies. The accuracy of ETSART was validated by comparing the calculated electron path lengths in semiconductor materials with the corresponding data in the ICRU Report 37. Using ETSART, we also computed the mean energy required to produce an electron–hole pair (epsilon value) in various semiconductors and found that the epsilon value varies nonlinearly with the bandgap energy. Thus, ETSART can be useful for initial and mechanistic evaluations of electron–hole pair formation in new materials.

Detection Limit of a NaI(Tl) Survey Meter to Measure <sup>131</sup>I Accumulation in Thyroid Glands of Children after a Nuclear Power Plant Accident

Background: This study examined the detection limit of thyroid screening monitoring conducted at the time of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 using a Monte Carlo simulation.Materials and Methods: We calculated the detection limit of a NaI(Tl) survey meter to measure 131I accumulation in the thyroid gland of children. Mathematical phantoms of 1- and 5-year-old children were developed in the simulation of the Particle and Heavy Ion Transport code System code. Contamination of the body surface with eight radionuclides found after the FDNPP accident was assumed to have been deposited on the neck and shoulder area.Results and Discussion: The detection limit was calculated as a function of ambient dose rate. In the case of 40 Bq/cm2 contamination on the body surface of the neck, the present simulations showed that residual thyroid radioactivity corresponding to thyroid dose of 100 mSv can be detected within 21 days after intake at the ambient dose rate of 0.2 μSv/hr and within 11 days in the case of 2.0 μSv/hr. When a time constant of 10 seconds was used at the dose rate of 0.2 μSv/hr, the estimated survey meter output error was 5%. Evaluation of the effect of individual differences in the location of the thyroid gland confirmed that the measured value would decrease by approximately 6% for a height difference of ±1 cm and increase by approximately 65% for a depth of 1 cm.Conclusion: In the event of a nuclear disaster, simple measurements carried out using a NaI(Tl) scintillation survey meter remain effective for assessing 131I intake. However, it should be noted that the presence of short-half-life radioactive materials on the body surface affects the detection limit.

Development of nuclear de-excitation model EBITEM Ver.2

ABSTRACT The gamma de-excitation model of the general-purpose radiation transport code Particle and Heavy Ion Transport code System, called the Evaluated Nuclear Structure Data File (ENSDF)-Based Isomeric Transition and isomEr production Model (EBITEM) has been upgraded with a focus on precise neutron-capture reaction simulation. The first de-excitation subsequent to neutron capture of numerous nuclei, which was formerly simulated by a model based on the single particle model, is calculated using the Evaluated Gamma Activation File. The database used for further de-excitation, ENSDF, retrieved in 2013, was replaced with Reference Input Parameter Library 3 to consider internal conversion. The internal conversion process was interfaced with the atomic de-excitation model to assess the emission of Auger electrons and fluorescent X-rays. The spectra of gamma-rays from neutron-capture reactions calculated by the upgraded EBITEM correlate better with the evaluated cross-section data than those of the previous version.

DOSIMETRY ANALYSIS OF BORON NEUTRON CAPTURE THERAPY (BNCT) ON THYROID CANCER USING PHITS CODE WITH NEUTRON FROM 30 MeV CYCLOTRON

The dosimetry analysis of Boron Neutron Capture Therapy (BNCT) on thyroid cancer using the Particle and Heavy Ion Transport Code System (PHITS) has been carried out. The purpose of research was to determine the received dose rate and the irradiation time required for thyroid cancer therapy using the BNCT method. The geometry of thyroid model is based on MIRD phantom with cancer cells located in the center of the thyroid. The phantom was irradiated using a neutron source from DLBSA based 30 MeV cyclotron. Simulations were carried out at boron concentrations of (10, 20, 30, 40, 50, 60, and 70) mg/g tissue. Simulation results show that the boron concentration increases with dose rate. The highest dose rate was obtained in the Gross Target Volume (GTV) of 1.590 x 10-2 Gy/s using a boron concentration of 70 mg/g tissue. The effective time for cancer therapy was calculated based on the highest dose rate obtained at 57 minutes.

Development of Directional 14 MeV-Fusion Neutron Detector Using Liquid-Scintillator-Filled Capillaries

Triton burnup studies have been performed in fusion experimental devices to evaluate the confinement performance of 3.5 MeV alpha particles. For this purpose, the generation rate of deuterium-tritium (D-T)-born 14 MeV neutrons has been measured using a scintillating fiber detector. The directionality of this detector provides excellent selectivity for 14 MeV neutrons; however, the lack of a pulse–shape discrimination (PSD) capability limits high-energy gamma-ray reduction. In this study, we developed a new 14 MeV neutron detector with directionality that can discriminate neutrons and gamma rays based on the PSD technique by filling capillaries with a liquid scintillator. The performance of this detector was evaluated at the FNL (Tohoku University, Japan) and OKTAVIAN (Osaka University, Japan). The detector response was modeled using the particle and heavy ion transport code system (PHITS). The experimental and simulation results demonstrated that the detector has a directional response to fast neutrons and excellent PSD capability.

Improvement of the hybrid approach between Monte Carlo simulation and analytical function for calculating microdosimetric probability densities in macroscopic matter

Objective. Estimation of the probability density of the microdosimetric quantities in macroscopic matter is indispensable for applying the concept of microdosimetry to medical physics and radiological protection. The Particle and Heavy Ion Transport code System (PHITS) enables estimating the microdosimetric probability densities due to its unique hybrid modality between the Monte Carlo and analytical approaches called the microdosimetric function. It can convert the deposition energies calculated by the macroscopic Monte Carlo radiation transport simulation to microdosimetric probability densities in water using an analytical function based on the track-structure simulations. Approach. In this study, we improved this function using the latest track-structure simulation codes implemented in PHITS. The improved function is capable of calculating the probability densities of not only the conventional microdosimetric quantities such as lineal energy but also the number of ionization events occurring in a target site, the so-called ionization cluster size distribution, for arbitrary site diameters from 3 nm to 1 μm. Main results. The accuracy of the improved function was well verified by comparing the microdosimetric probability densities measured by tissue-equivalent proportional counters with the corresponding data calculated in this study. Test calculations for clonogenic cell survival using the improved function coupled with the modified microdosimetric kinetic model suggested a slight increase of its relative biological effectiveness compared with our previous estimations. As a new application of the improved function, we calculated the relative biological effectiveness of the single-strand break and double-strand break yields for proton irradiations using the updated PHITS coupled with the simplified DNA damage estimation model, and confirmed its equivalence in accuracy and its superiority in computational time compared to our previously proposed method based on the track-structure simulation. Significance. From these features, we concluded that the improved function could expand the application fields of PHITS by bridging the gap between microdosimetry and macrodosimetry.

Monte Carlo Simulation Study on the Optimal Neutron Energy and Boron Concentration for SARS-COV-2 Inactivation through BNCT

Researchers have been exploring various radiation therapies to treat COVID-19 patients ranging from mild to severe. One technique that has shown promise is Boron Neutron Capture Therapy (BNCT). This therapy involves administering of 10B isotope to the targeted area, which is then exposed to chargeless neutrons. These neutrons can be absorbed by areas with high concentrations of 10B. When the neutrons react with the 10B (10B + n?7Li + 4He reaction), it results in the transfer of highly ionizing energy, causing confined lethality and destroying the targeted area. In this study, we used the Particle and Heavy Ion Transport Code System simulation to evaluate whether Boron Neutron Capture Therapy could be effective as an anti-viral therapy. The study involves creating a model of the SAR-COV-2 target phantom's geometry and defining its chemical composition to collect data. It was found out that when tested at different neutron energies and concentrations (30 ppm, 50 ppm, and 100 ppm), a sufficient amount of dose to cause biological damage to the Sars-CoV-2 enveloped protein could be achieved with 30 ppm boron concentration and a neutron energy of 1.0x10-10 MeV.

Monte Carlo Simulation to Test the Effectiveness of Crystal Detector Length for PHITS-Based PET Modality

PET (Positron-emission tomography) is used to determine physiological and metabolic functions in the body. Monte Carlo simulation is an important part of PET imaging, and the Particle Heavy Ion Transport code System (PHITS) is a simulation platform that can be used to perform Monte Carlo simulations. This study uses a Monte Carlo simulation based on PHITS to determine the range of gamma absorption with an energy of 511 keV in a scintillation detector crystal material. The gamma absorption range determines the effective crystal length in the PET modality. The simulation process is carried out by shooting Gamma at various types of materials, which are the materials used in PET scintillation crystals. The materials used in this simulation are NaI (Sodium Iodide), BaF2 (Barium Florida), BGO (Bismuth Germanate), and GSO (Gadolinium Oxyorthosilicate), considering their atomic number and crystal density. The crystal material is capable of absorbing gamma radiation with an energy of 511 keV with detailed crystal lengths for each NaI crystal of 0.26 cm; 0.25 cm BaF2 crystals; 0.1cm BGO crystals; and 0.18 cm GSO crystals. The crystal length from this simulation is smaller than the commercially available crystal length (range 1-3 cm). Based on the crystal length data, the most effective crystal for absorbing gamma radiation is the BGO crystal.

MONTE CARLO NEUTRON DOSE MEASUREMENT IN PROTON THERAPY FOR HEALTHCARE WORKER RADIATION SAFETY

Background: Proton therapy is an innovative and highly advanced external radiation therapy modality for cancer treatment that uses positively charged atomic particles. The usage of proton therapy facilities in Asia has been increasing and will be followed by Indonesia in the short-coming years. In line with its significant benefits, the application of proton therapy also requires radiation protection awareness due to its higher energy used by protons produces scattered photon and neutron radiation in proton interactions. Therefore, optimal verification is needed in the commissioning process for designing proton therapy shielding bunkers. Objective: This research aims to examine the effect of concrete density on proton shielding by calculating the equivalent dose H*(10) of neutrons in the treatment control room (TCR) and the door of the compact proton therapy facility (CPTC) using Particle and Heavy Ion Transport code System (PHITS) simulation software. Method: The proton facility modeled for this simulation uses a compact proton therapy type planned to be built at one of the radiotherapy facilities in Indonesia. The proton therapy bunker model consists of a synchrocyclotron accelerator room and an examination room with standard configurations, wall thicknesses, and modeling areas under compact proton therapy standards. The analysis is focused on assessing the suitability of concrete materials and wall thicknesses and determining the neutron exposure dose values in the TCR and CPTC doors. The geometry, radiation source, and type of concrete in the wall are simulated from a conservative assumption to a more realistic model. Result: At the designated points in the TCR and CPTC door, measurements are taken from the simulation, which indicates that the equivalent dose H*(10) value is below one mSv/year. Conclusion: This value indicates that the dose rate passing through the wall does not exceed the dose limit value already set at one mSv/year for the general public.

Dose analysis of Boron Neutron Capture Therapy (BNCT) on head cancer using PHITS code with neutron source from accelerator

The dose analysis of Boron Neutron Capture Therapy (BNCT) on head cancer using the Particle and Heavy Ion Transport Code System (PHITS) has been carried out. The purpose of this study was determine the rate of dose received and the irradiation time required for head cancer therapy using the BNCT method. The research was conducted through a simulation approach. The PHITS code was used to design an epithermal neutron source derived from accelerator and to define the geometric dimensions of the head tissue components. The head model is based on Snyder’s head model with cancer cells located in the center of the brain at a depth of 3.8 cm. The investigation of the dose distribution on the head included skin, skull, brain and cancer sections consisting of Planning Target Volume (PTV), Clinical Target Volume (CTV) and Gross Tumor Volume (GTV). Simulations were carried out at boron concentrations of 30, 40, 50, 60, 70, and 80 μg/g tissue. Based on the simulation results, the greater the boron concentration, the greater the resulting dose rate. The highest dose rate was obtained in the GTV area of 6.37 x 10-2 Gy/s using a boron concentration of 80 μg/g tissue. The effective time for cancer therapy was calculated based on the highest dose rate obtained at 13,08 minutes.

Boron neutron capture therapy in the new age of accelerator-based neutron production and preliminary progress in Canada

Each year more than 3000 Canadians are diagnosed with brain cancers like glioblastoma multiforme or recurrent head and neck cancers, which are difficult to treat with conventional radiotherapy techniques. One of the most clinically promising treatments for these cancers is boron neutron capture therapy (BNCT). This procedure involves selectively introducing a boron delivery agent into tumor cells and irradiating them with a neutron beam, which kills the cancer cells due to the high-linear energy transfer radiation produced by the 10B(n,α)7Li capture reaction. The theory of BNCT has been around for a long time since 1936, but has historically been limited by poor boron delivery agents and non-optimal neutron source facilities. Although significant improvements have been made in both of these domains, it is mainly the advancements of accelerator-based neutron sources that have led to the expansion of over 20 new BNCT facilities worldwide in the past decade. Additionally in this work, particle and heavy ion transport code system simulations, in collaboration with the University of Tsukuba, were performed to examine the effectiveness of the Ibaraki BNCT beam shaping assembly to moderate a neutron beam suitable for BNCT at the proposed prototype Canadian compact accelerator-based neutron source (CANS) site, which uses a similar but slightly higher energy 10 MeV proton accelerator with a 1 mA average current. The advancements of CANSs in recent decades have enabled significant improvements in BNCT technologies, allowing it to become a more viable clinical treatment option.

Virtual Reality System for Monte Carlo Transport Simulation Codes Using Web Technology and Commodity Devices

A virtual reality (VR) system for Monte Carlo (MC) transport simulation codes, MCNP and Particle and Heavy Ion Transport Code System (PHITS), was developed. This system is aimed to provide a more reliable confirmation of the simulation geometry through an intuitive user interface. The VR system is implemented by extending the Geometry and CROSS Section VIEWer (Gxsview) code to run in a JavaScript environment, and it takes advantage of web technology and does not require dedicated hardware or geometry information supplied by computer-aided design software. Therefore, only WebXR-compatible head-mounted displays and browsers are required on the user side. In the VR space, visualization of the calculation geometry, cell selection, and cell grabbing operations is possible with a handheld controller. Further enhancements will be made in the future, such as performing shielding calculations with the cell changed by grabbing operations.

Dose estimation for cone-beam computed tomography in image-guided radiation therapy for pelvic cancer using adult mesh-type reference computational phantoms

The use of cone-beam computed tomography (CBCT) is expanding owing to its installation in linear accelerators for radiation therapy, and the imaging dose induced by this system has become the center of attention. Here, the dose to patients caused by the CBCT imager was investigated. Organ doses and effective doses for male and female mesh-type reference computational phantoms (MRCPs) and pelvis CBCT mode, routinely used for pelvic irradiation, were estimated using the Particle and Heavy Ion Transport Code System. The simulation results were confirmed based on the point-dose measurements. The estimated organ doses for male MRCPs with/without raised arms and for female MRCPs with/without raised arms were 0.00286-35.6mGy, 0.00286-35.1mGy, 0.00933-39.5mGy, and 0.00931-39.0mGy, respectively. The anticipated effective doses for male MRCPs with/without raised arms and female MRCPs with/without raised arms irradiated by pelvis CBCT mode were 4.25mSv, 4.16mSv, 7.66mSv, and 7.48mSv, respectively. The results of this study will be useful for patients who undergo image-guided radiotherapy with CBCT. However, because this study only covered one type of cancer with one type of imager, and image quality was not considered, more studies should be conducted to estimate the radiation dose from imaging devices in radiation therapy.

Photon dose rate distribution inside and outside a brachytherapy room.

In a brachytherapy room irradiated with an Iridium-192 (192Ir) source, the spatial distributions of photon dose rates were measured and calculated for the dose distribution both inside and outside the room. The spatial distributions were measured using a thermoluminescent dosimeter (LiF-100) on the surfaces of the concrete walls and barriers of the irradiation room. The calculations were performed using the particle and heavy ion transport code system (PHITS) by considering the detailed model of the brachytherapy room and the radiation source used in the measurements. The measured and calculated doses exhibited a similar distribution pattern within and outside the brachytherapy room. To reduce the edge effect at the entrance door, the addition of a 3-mm thick lead layer on the surface of the concrete wall on the left doorstop is recommended. For the 60Co source, with the existing walls and lead door thickness, the dose at the control console and in front of the entrance maze increased by a factor of approximately 60.

Benchmark shielding calculations for fusion and accelerator-driven sub-critical systems

We conducted benchmark calculations of neutron-shielding experiments for fusion applications such as (1) Neutron spectra in iron shields with 14 MeV neutrons; and (2) Leakage neutron spectra from various sphere piles by 14 MeV neutrons, and for Accelerator-Driven Sub-Critical system (ADS) such as (3) Neutron energy spectra after transmission through iron and concrete shields using a quasi-monochromatic neutron source, (4) Thick target neutron yield produced by high-energy heavy ion incidence on a thick target, and (5) Induced radio activity in concrete exposed to secondary particles produced by heavy-ion incident reaction on an iron target by using the Particle and Heavy Ion Transport code System (PHITS). For case (1), the calculated neutron energy spectra using the nuclear data libraries, JENDL-4.0, agreed with the experimental data in iron shields. For the cases (2) of Al, Ti, Cr, and As piles, the neutron energy spectra calculated with JENDL-4.0 agreed with the experimental results well. For the case (3), the neutron spectra calculated with JENDL-4.0/HE reproduced the experimental data because the proton data library of7Li can produce source neutrons for proton incident reactions. For the case (4), calculated results for thick target neutron spectra produced by a 400 MeV per nucleon carbon incident reaction on lead reproduced the experimental data well. For the case (5) with a neutron source produced by the 200–400 MeV per nucleon heavy-ion incident reaction, the calculated results of the reaction rate depth profiles of197Au (n, γ)198Au reactions reproduced the experimental results within a factor of 2. Overall, PHITS with nuclear data libraries reproduced the experimental data sufficiently well. Thus, PHITS has a potential application in the design of advanced reactor systems, such as fusion and ADS facilities. This experimental data are also useful in validating nuclear reaction models in other Monte Carlo codes and evaluating nuclear data libraries for advanced reactor systems.

Neutron shielding assessment of a 16O hadron therapy room by means of Monte Carlo simulations with the PHITS code

Hadron radiation therapy is of great interest worldwide. Heavy-ion beams provide ideal therapeutic conditions for deep-seated local tumours. At the Heidelberg Ion Beam Therapy Center (HIT, Germany), protons and carbon ions are already integrated into the clinical routine, while 16O ions are still used for research only. To ensure the protection of the technical staff and members of the public, it is required to estimate the neutron dose distribution for optimal working conditions and at different locations. The Particle and Heavy Ion Transport Code System (PHITS) is used in this work to evaluate the dose rate distribution of secondary neutrons in a treatment room at HIT where 16O ions are used: an equivalent target in soft tissue is considered in the shielding assessment to simulate the interaction of the beam with patients. The angular dependence of neutron fluences and energy spectra around the considered phantom were calculated. Alongside the spatial distribution of the neutron and photon fluence, a map of the effective dose rate was estimated using the ICRP fluence-to-effective dose conversion coefficients, exploiting the PHITS code’s built-in capabilities. The capability of the actual shielding design of the studied HIT treatment room was approved.

An Analytical Method for Quantifying the Yields of DNA Double-Strand Breaks Coupled with Strand Breaks by γ-H2AX Focus Formation Assay Based on Track-Structure Simulation.

Complex DNA double-strand break (DSB), which is defined as a DSB coupled with additional strand breaks within 10 bp in this study, induced after ionizing radiation or X-rays, is recognized as fatal damage which can induce cell death with a certain probability. In general, a DSB site inside the nucleus of live cells can be experimentally detected using the γ-H2AX focus formation assay. DSB complexity is believed to be detected by analyzing the focus size using such an assay. However, the relationship between focus size and DSB complexity remains uncertain. In this study, using Monte Carlo (MC) track-structure simulation codes, i.e., an in-house WLTrack code and a Particle and Heavy Ion Transport code System (PHITS), we developed an analytical method for qualifying the DSB complexity induced by photon irradiation from the microscopic image of γ-H2AX foci. First, assuming that events (i.e., ionization and excitation) potentially induce DNA strand breaks, we scored the number of events in a water cube (5.03 × 5.03 × 5.03 nm3) along electron tracks. Second, we obtained the relationship between the number of events and the foci size experimentally measured by the γ-H2AX focus formation assay. Third, using this relationship, we evaluated the degree of DSB complexity induced after photon irradiation for various X-ray spectra using the foci size, and the experimental DSB complexity was compared to the results estimated by the well-verified DNA damage estimation model in the PHITS code. The number of events in a water cube was found to be proportional to foci size, suggesting that the number of events intrinsically related to DSB complexity at the DNA scale. The developed method was applicable to focus data measured for various X-ray spectral situations (i.e., diagnostic kV X-rays and therapeutic MV X-rays). This method would contribute to a precise understanding of the early biological impacts of photon irradiation by means of the γ-H2AX focus formation assay.