Matsuya, Yusuke; Sato, Tatsuhiko; Nakamura, Rui*; Naijo, Shingo*; Date, Hiroyuki*
Physics in Medicine and Biology, 65(9), p.095006_1 - 095006_12, 2020/05
Radio-resistance induced under low oxygen pressure plays an important role in malignant progression in fractionated radiotherapy. For the general approach to predict cell killing under hypoxia, cell-killing models (e.g., the Linear-Quadratic model) have to be fitted to experimental survival data for both normoxia and hypoxia to obtain the oxygen enhancement ratio (OER). However, model parameters for every oxygen condition needs to be considered by model-fitting approaches. This is inefficient for fractionated irradiation planning. Here, we present an efficient model for fractionated radiotherapy the integrated microdosimetric-kinetic model including cell-cycle distribution and the OER at DNA double-strand break endpoint. The cell survival curves described by this model can reproduce the experimental survival data for both acute and chronic low oxygen concentrations. The OER used for calculating cell survival agrees well with experimental DSB ratio of normoxia to hypoxia. This work provides biological effective dose (BED) under various oxygen conditions including its uncertainty, which can contribute to creating fractionated regimens for multi-fractionated radiotherapy. If the oxygen concentration in a tumor can be quantified by medical imaging, the present model will make it possible to estimate the cell-killing and BED under hypoxia in more realistic intravital situations.
El Basha, D.*; Furuta, Takuya; Iyer, S. S. R.*; Bolch, W. E.*
Physics in Medicine and Biology, 63(10), p.105017_1 - 105017_13, 2018/05
With recent changes in the recommended annual limit on eye lens exposures to ionizing radiation by International Commission on Radiological Protection, there is considerable interest in predictive computational dosimetry models of the human eye and its various ocular structures. Several computational eye models to date have been constructed for this purpose but they are typically constructed of nominal size and of a roughly spherical shape associated with the emmetropic eye. We therefore constructed a geometric eye model that is both scalable (allowing for changes in eye size) and deformable (allowing for changes in eye shape), and that is suitable for use in radiation transport studies of ocular exposures and radiation treatments of eye disease. As an example, electron and photon anterior-posterior radiation transport with the constructed eye model was conducted and analyzed resultant energy-dependent dose profiles. Due to anterior-posterior irradiation, the energy dose response was shifted to higher energy for a larger-size eye or an axially deformed eye in prolate shape because the structures were located in deeper depth compared to the normal eye.
Han, M. C.*; Yeom, Y. S.*; Lee, H. S.*; Shin, B.*; Kim, C. H.*; Furuta, Takuya
Physics in Medicine and Biology, 63(9), p.09NT02_1 - 09NT02_9, 2018/05
The multi-threading computation performances of the Geant4, MCNP6, and PHITS codes were evaluated using three tetrahedral-mesh phantoms with different complexity. Photon and neutron transport simulations were conducted and the initialization time, calculation time, and memory usage were measured as a function of the number of threads N used in the simulation. The initialization time significantly increases with the complexity of the phantom, but not much with the number of the threads. For the calculation time, Geant4 showed good parallelization efficiency with multi-thread computation (30 times speed-up factor for N = 40) adopting the private tallies while saturation of the speed-up factor were observed in MCNP6 and PHITS (10 and a few times for N = 40) due to the time delay for the sharing tallies. On the other hand, Geant4 requires larger memory specification and the memory usage rapidly increases with the number of threads compared to MCNP6 or PHITS. It is notable that when compared to the other codes, the memory usage of PHITS is much smaller, regardless of both the complexity of the phantom and the number of the threads.
Furuta, Takuya; Sato, Tatsuhiko; Han, M. C.*; Yeom, Y. S.*; Kim, C. H.*; Brown, J. L.*; Bolch, W. E.*
Physics in Medicine and Biology, 62(12), p.4798 - 4810, 2017/06
A new function to treat tetrahedral-mesh geometry, a type of polygon-mesh geometry, was implemented in the Particle and Heavy Ion Transport code Systems (PHITS). Tetrahedral-mesh is suitable to describe complex geometry including curving shapes. In addition, construction of three-dimensional geometry using CAD software becomes possible with file format conversion. We have introduced a function to create decomposition maps of tetrahedral-mesh objects at the initial process so that the computational time for transport process can be reduced. Owing to this function, transport calculation in tetrahedral-mesh geometry can be as fast as that for the geometry in voxel-mesh with the same number of meshes. Due to adaptability of tetrahedrons in size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with much fewer number of meshes compared with the voxels. For dosimetric calculation using computational human phantom, significant acceleration of the computational speed, about 4 times, was confirmed by adopting the tetrahedral mesh instead of the voxel.
Furuta, Takuya; Maeyama, Takuya*; Ishikawa, Kenichi*; Fukunishi, Nobuhisa*; Fukasaku, Kazuaki*; Takagi, Shu*; Noda, Shigeho*; Himeno, Ryutaro*; Hayashi, Shinichiro*
Physics in Medicine and Biology, 60(16), p.6531 - 6546, 2015/08
Low reproducibility of dose distribution in inhomogeneous regions such as soft matter near bones is known with the simple dose analysis currently adopted in treatment planning of particle cancer therapy. Therefore a treatment planning system based on Monte Carlo simulation having better accuracy is highly desired. In order to assess the simulation accuracy of a Monte Carlo simulation code in situations closely related to medical application, we performed a comparison of dose distribution in a biological sample obtained by experiment and that by simulation. In particular, we irradiate a carbon beam on a biological sample composed of fresh chicken meat and bones, with a PAGAT gel dosimeter placed behind it, and compare the complex dose distribution in the gel dosimeter created by the beam passing through the inhomogeneous sample. Monte Carlo simulation using PHITS code was conducted by reconstructing the biological sample from its computed tomography images. The simulation accurately reproduced the experimental distal edge structure of the dose distribution with an accuracy under about 2 mm.
Polster, L.*; Schuemann, J.*; Rinaldi, I.*; Burigo, L.*; McNamara, A. L.*; Steward, R. D.*; Attili, A.*; Carlson, D. J.*; Sato, Tatsuhiko; Ramos Mndez, J.*; et al.
Physics in Medicine and Biology, 60(13), p.5053 - 5070, 2015/07
The aim of this work is to extend a widely used proton Monte Carlo tool, TOPAS, towards the modeling of relative biological effect (RBE) distributions in experimental arrangements as well as patients. Then, eight biophysical models was incorporated into TOPAS. As far as physics parameters are concerned, four of these models are based on the proton linear energy transfer (LET), while the others are based on DNA Double Strand Break (DSB) induction and the frequency-mean specific energy, lineal energy, or delta electron generated track structure. The model on the basis of lineal energy adapted a microdosimetric function developed by JAEA. This work is an important step in bringing biologically optimized treatment planning for proton therapy closer to the clinical practice.
Petoussi-Henss, N.*; Bolch, W. E.*; Eckerman, K. F.*; Endo, Akira; Hertel, N.*; Hunt, J.*; Menzel, H. G.*; Pelliccioni, M.*; Schlattl, H.*; Zankl, M.*
Physics in Medicine and Biology, 59(18), p.5209 - 5224, 2014/09
ICRP Publication 116 (ICRP116) on "Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposures", provides fluence-to-dose conversion coefficients for organ absorbed doses and effective dose for external exposures. ICRP116 supersedes the ICRP74, expanding also the particle types and energy ranges considered. The coefficients were calculated using the ICRP/ICRU computational phantoms representing the Reference Adult Male and Reference Adult Female, together with Monte Carlo codes simulating the radiation transport in the body. Idealised whole-body irradiation from unidirectional and rotational parallel beams as well as isotropic irradiation was considered. Comparison of the effective doses with operational quantities revealed that the latter quantities continue to provide a good approximation of effective dose for photons, neutrons and electrons for the conventional energy ranges considered previously, but not at the higher energies of ICRP116.
Manabe, Kentaro; Sato, Kaoru; Endo, Akira
Physics in Medicine and Biology, 59(5), p.1255 - 1270, 2014/03
The International Commission on Radiological Protection (ICRP) decided to use reference phantoms based on physical characteristics of basic Caucasian in evaluation of effective doses in the ICRP 2007 Recommendations. Specific absorbed fractions (SAFs), which are essential data for internal dosimetry, depend on physical characteristics of a phantom used in calculating the SAFs. The body size and amount of adipose tissue of adult Japanese are generally smaller than that of Caucasian. Then, we studied the effects of differences in physical characteristics on internal doses. The electron and photon SAFs of the average adult Japanese male phantom (JM-103) were calculated with the Monte Carlo method, MCNPX. The electron SAFs of the ICRP reference computational phantom-adult male (RCP-AM) were taken from published data. The photon SAFs of the RCP-AM were calculated in the same way as JM-103. Then, the values corresponding to effective dose coefficients for intakes of radionuclides were calculated using the SAFs of these phantoms. As a result of a comparison for 2894 cases of 923 radionuclides, the maximum discrepancy in the effective dose coefficients between the JM-103 and RCP-AM was about 40%. However, the discrepancies were smaller than 10% in 97% of all cases. Information obtained in this study is helpful in applying the dose coefficients of the ICRP to races other than Caucasian.
Hiroki, Akihiro; Sato, Yuichi*; Nagasawa, Naotsugu; Ota, Akio*; Seito, Hajime; Yamabayashi, Hisamichi*; Yamamoto, Takayoshi*; Taguchi, Mitsumasa; Tamada, Masao; Kojima, Takuji
Physics in Medicine and Biology, 58(20), p.7131 - 7141, 2013/10
Bahadori, A. A.*; Sato, Tatsuhiko; Slaba, T. C.*; Shavers, M. R.*; Semones, E. J.*; Baalen, M. V.*; Bolch, W. E.*
Physics in Medicine and Biology, 58(20), p.7183 - 7207, 2013/10
In the present study, organ absorbed doses and dose equivalents are calculated for 50th percentile male and female astronaut phantoms using both the NASA High Charge and Energy Transport Code (HZETRN) to perform one-dimensional deterministic transport and using the Particle and Heavy Ion Transport code System (PHITS) to perform three-dimensional Monte Carlo transport. Code-to-code benchmarks allow for the comparison of differential quantities, such as secondary particle differential fluence, to provide insight into differences observed in integral quantities for particular components of the GCR spectrum.
Yamaguchi, Mitsutaka; Torikai, Kota*; Kawachi, Naoki; Shimada, Hirofumi*; Sato, Takahiro; Nagao, Yuto; Fujimaki, Shu; Kokubun, Motohide*; Watanabe, Shin*; Takahashi, Tadayuki*; et al.
Physics in Medicine and Biology, 57(10), p.2843 - 2856, 2012/05
Tsuda, Shuichi; Sato, Tatsuhiko; Takahashi, Fumiaki; Satoh, Daiki; Endo, Akira; Sasaki, Shinichi*; Namito, Yoshihito*; Iwase, Hiroshi*; Ban, Shuichi*; Takada, Masashi*
Physics in Medicine and Biology, 55(17), p.5089 - 5101, 2010/09
The frequency distribution of the lineal energy of 290 MeV/u carbon beam was measured using a wall-less tissue equivalent proportional counter (wall-less TEPC) in a cylindrical volume with simulated diameter 0.72 m in verifying the accuracy of a dose calculation model. The measured lineal energy distribution as well as its dose-mean value agreed fairly well with the corresponding data from microdosimetric calculations using the PHITS code within the experimental uncertainty. It is found that a wall-less TEPC is needed to measure the precise energy deposition spectra of the delta rays produced secondarily by energetic heavy ion beams. The measured data also indicate that more than 11% of the energy escaped from the path of the trajectory of the carbon beam.
Sato, Tatsuhiko; Endo, Akira; Niita, Koji*
Physics in Medicine and Biology, 55(8), p.2235 - 2246, 2010/04
The fluence to organ-dose and effective-dose conversion coefficients for heavy ions with atomic numbers up to 28 and energies from 1 MeV/nucleon to 100 GeV/nucleon were calculated using the PHITS code coupled to the ICRP/ICRU adult reference computational phantoms, following the instruction given in ICRP Publication 103.
Sato, Tatsuhiko; Endo, Akira; Zankl, M.*; Petoussi-Henss, N.*; Niita, Koji*
Physics in Medicine and Biology, 54(7), p.1997 - 2014, 2009/04
The fluence to organ-dose and effective-dose conversion coefficients for neutrons and protons with energies up to 100 GeV were calculated using the PHITS code coupled to the male and female adult reference computational phantoms, which are to be released as a common ICRP/ICRU publication. For the calculation, the radiation and tissue weighting factors, wR and wT, as revised in ICRP Publication 103 were employed. The calculated data of these dose conversion coefficients are indispensable for constructing the radiation protection systems based on the new recommendations given in ICRP103 for aircrews and astronauts, as well as for workers in accelerators and nuclear facilities.
Sato, Kaoru; Endo, Akira
Physics in Medicine and Biology, 53(17), p.4555 - 4572, 2008/09
In order to clarify the effects of posture on organ doses due to internal exposures, SAFs for photons from 0.01 to 4 MeV were calculated using JM2 (upright) and JM (supine) phantoms whose designs were based on CT images of two postures obtained from the same person. Differences in the SAFs of JM2 and JM are within a factor of 2 in most cases, although significant differences in SAFs exist in several cases for low energy photons. Organ doses due to photons from intake of unit activity of 8 radionuclides with different biokinetics and decay characteristics were calculated from the SAFs of JM2 and JM. It was found the organ doses in the testes, bone marrow, lower large intestine wall, lungs and stomach wall, which are important for calculating effective dose, in the two postures roughly agree, the maximum difference being 14%. These results indicate that the impact of posture on the organ doses and effective doses from internal photon emitters is limited.
Yamamoto, Tetsuya*; Matsumura, Akira*; Yamamoto, Kazuyoshi; Kumada, Hiroaki; Shibata, Yasushi*; Nose, Tadao*
Physics in Medicine and Biology, 47(14), p.2387 - 2396, 2002/07
The aim of this study was to determine the in-phantom thermal distribution derived from neutron beams for intraoperative boron neutron capture therapy (IOBNCT). Gold activation wires arranged in a cylindrical water phantom with (void-in phantom) or without (standard phantom) a cylinder styrene form placed inside were irradiated by using the epithermal beam (ENB) and the mixed thermal-epithermal beam (TNB-1) at the JRR-4. The thermal neutron distribution derived from both the ENB and TNB-1 was significantly improved in the void-in-phantom, and a double high dose area was formed lateral to the void. The flattened distribution in the circumference of the void was observed with the combination of ENB and the void-in-phantom. The measurement data suggest that the ENB may provide a clinical advantage in the form of an enhanced and flattened dose delivery to the marginal tissue in which residual and/or microscopically infiltrating tumor.