| 1. |
- Lee, Boon Q, et al.
(författare)
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A stochastic cascade model for Auger-electron emitting radionuclides
- 2016
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Ingår i: International Journal of Radiation Biology. - : Taylor & Francis. - 0955-3002 .- 1362-3095. ; 92:11, s. 641-653
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Tidskriftsartikel (refereegranskat)abstract
- To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Sch€onfeld’s algorithms and the BRICC code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z¼1–100. Atomic transition energies were evaluated using a relativistic Dirac- Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of 123I, 124I, and 125I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study.
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| 2. |
- Liamsuwan, Thiansin, et al.
(författare)
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A model of carbon ion interactions in water using the classical trajectory Monte Carlo method
- 2011
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Ingår i: International Journal of Radiation Biology. - : Oxford University Press (OUP). - 0955-3002 .- 1362-3095. ; 143:2-4, s. 152-155
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, model calculations for interactions of C6+ of energies from 1 keV u−1 to 1 MeV u−1 in water are presented. The calculations were carried out using the classical trajectory Monte Carlo method, taking into account the dynamic screening of the target core. The total cross sections (TCS) for electron capture and ionisation, and the singly and doubly differential cross sections (SDCS and DDCS) for ionisation were calculated for the five potential energy levels of the water molecule. The peaks in the DDCS for the electron capture to continuum and for the binary-encounter collision were obtained for 500-keV u−1 carbon ions. The calculated SDCS agree reasonably well with the z2 scaled proton data for 500 keV u−1 and 1 MeV u−1 projectiles, but a large deviation of up to 8-folds was observed for 100-keV u−1 projectiles. The TCS for ionisation are in agreement with the values calculated from the first born approximation (FBA) at the highest energy region investigated, but become smaller than the values from the FBA at the lower-energy region.
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| 3. |
- Liamsuwan, Thiansin, et al.
(författare)
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A Monte Carlo track structure simulation code for the full-slowing-down carbon projectiles of energies 1 keV u-1–10 MeV u-1 in water
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58:3, s. 673-702
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a new Monte Carlo track structure code (KURBUC_carbon) for simulations of full slowing down carbon projectiles C0–C6+ of energies 1 keV/u–10 MeV/u in water vapour. The code facilitates investigation of spatial resolution effect for scoring track parameters under the Bragg peak of carbon ion beam. Interactions of carbon projectiles and secondary electrons were followed event-by-event down to 1 keV/u cutoff for primary ions, and down to 10 eV for electrons. Electronic interactions and nuclear elastic scattering were taken into account, including charge exchange reactions and double electronic interactions for the carbon projectiles. The reliability of the code was tested for radial dose, range, and W-value. The calculated results were compared with the published experimental data, and other model calculations. The results obtained showed good agreement in most cases where comparisons could be made. Depth dose profiles for 1-10 MeV/u C6+ were used to form an SOBP of 0.35 mm width in water. At all depths of the SOBP, the energy distributions of the carbon projectiles varied appreciably with the change in the scoring volume. The corresponding variation was nearly negligible for the track average LET, except at the distal end of the SOBP. By varying the scoring slab thickness from 1 to 100 µm, the maximum track average LET decreased by ~30%. The Monte Carlo track structure simulation in the full slowing down mode is a powerful tool for investigation of biophysical properties of radiation tracks under the Bragg peak and SOBP of carbon ion beam. For estimation of radiation effectiveness under the Bragg peak the new Monte Carlo track structure code provides yet another accurate and effective dosimetry tool at a single cell level. This is because radiobiology within tissue elements can only be understood with dosimetry at cellular and subcellular level.
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| 4. |
- Liamsuwan, Thiansin, 1984-, et al.
(författare)
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An energy-loss model for low- and intermediate-energy carbon projectiles in water
- 2012
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 88:1-2, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To model interaction cross sections and energy loss for carbon projectiles C(0)-C(6+) of 1-10(4) keV/u (u: atomic mass unit) in water. Materials and methods: The classical trajectory Monte Carlo method was used to calculate the ionisation and charge-transfer cross sections. The excitation cross sections were scaled from proton data using equilibrium charges determined from the charge-transfer cross sections. Energy loss was obtained from the singly differential cross sections, and ionisation potentials of the target and projectile. Results: The calculated total ionisation cross sections are consistent with measured data, while the calculated electron-capture cross sections are larger than experimental data by a factor of 3. By scaling the latter to the measured data, the cross sections were made consistent with these data for 1-10 keV/u energies. The present stopping cross sections agree well with experimental data below 10 keV/u, and with other model calculations above 2 MeV/u. Deviation from the latter is found where electron capture is competitive with ionisation, and also arises from different energy-transfer calculations. Conclusions: In this paper we report our efforts in the developments of full slowing-down Monte Carlo track structure calculations for carbon ions. Further development and refinement of the model are currently underway.
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| 5. |
- Liamsuwan, Thiansin, et al.
(författare)
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Cross sections for bare and dressed carbon ions in water and neon
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58, s. 641-672
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents calculated cross sections for bare and dressed carbon projectiles of charge states q (0 to 6) with energies 1–104 keV/u impacting on molecular water and atomic neon targets. The cross sections of water are of interest for radiobiological studies, but there are very few experimental data for water in any phase or non-existent. The more extensive experimental database for the neon target made it possible to test the reliability of the model calculations for many-electron collision system. The current calculations cover major single and double electronic interactions of low and intermediate energy carbon projectiles. The three-body classical trajectory Monte Carlo (CTMC) method was used for the calculation of one-electron transition probabilities for target ionisation, electron capture, and projectile electron loss. The many-electron problem was taken into account using statistical methods: a modified independent event model was used for pure (direct) and simultaneous target and projectile ionisations; and the independent particle model for pure electron capture and electron capture accompanied by target ionisation. Results are presented for double differential cross sections (DDCS) for total electron emission by carbon projectile impact on neon. For the water target, we present: single differential cross sections (SDCS) and DDCS for single target ionisation; total cross sections (TCS) for electron emission; TCS for the pure single electronic interactions; equilibrium charge state fractions; and stopping cross sections. The results were found to be in satisfactory agreement with the experimental data in many cases, including DDCS and SDCS for the single target ionisation, TCS for the total electron emission, and TCS for the pure single electron capture. The stopping cross sections of this work are consistent with the other model calculations for projectile energies ≥800 keV/u, but smaller than the other calculations at lower energies. The discrepancy arises from the inclusion of all carbon charge states and coupling between electron capture and target ionisation channels, while other models use an average projectile charge. The CTMC model presented here provides a tool for cross section calculations for low and intermediate energy carbon projectiles. The calculated cross sections are required for Monte Carlo track structure simulations of full-slowing-down tracks of carbon ions. The work paves the way for biophysical studies and dosimetry at the cellular and subcellular levels in the Bragg peak area of therapeutic carbon ion beam.
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| 6. |
- Liamsuwan, Thiansin, 1984-
(författare)
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Development of Monte Carlo track structure simulations for protons and carbon ions in water
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The goal of radiation therapy is to eradicate tumour cells while minimising radiation dose to healthy tissues. Ions including protons and carbon ions have gained increasing interest for cancer treatment. Advantages of ion beam therapy are conformal dose distribution, and for ions heavier than protons increased biological effectiveness in cell killing, compared to conventional radiation therapy using photons. Despite these advantages, fundamental problems in ion beam therapy include accuracy of dose determination at the cellular level, and characterisation of the radiation quality at the microscopic scale. Due to the high density of interactions along ion tracks, inhomogeneity of dose and track parameters at the cellular level is one of the major concerns for ion beam therapy.The aim of the thesis is to develop computational tools for dosimetry of ion tracks at the molecular level. Event-by-event Monte Carlo track structure (MCTS) simulations were developed for full-slowing-down tracks of protons and carbon ions in water representing cellular environment. In Paper I, the extension of the MCTS code KURBUC_proton was carried out to energies up to 300 MeV, covering the entire proton energy range used in radiation therapy. Physical properties and microdosimetry of proton tracks were investigated and benchmarked with the experimental data. Papers II-V describe the development of the MCTS code for full-slowing-down tracks of carbon ions. In Papers II-IV, the classical trajectory Monte Carlo (CTMC) model was developed for the calculation of interaction cross sections for low and intermediate energy carbon projectiles of all charge states (C0 to C6+) in water. In Paper V, the calculated cross sections were implemented in a new MCTS code KURBUC_carbon simulating carbon ions of energies 1-104 keV/u in water. This development allows the investigation of track parameters in the Bragg peak region of carbon ion beams.Publication of the thesis and the published papers make contribution to the physics of ion interactions in matter, and provide a new and complete database of electronic interaction cross sections for low and intermediate energy carbon projectiles of all charge states in water. The MCTS codes for protons and carbon ions provide new tools for biophysical study, including microdosimetry, of ion tracks at cellular and subcellular levels, in particular in the Bragg peak region of these ions.
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| 7. |
- Liamsuwan, Thiansin, et al.
(författare)
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Microdosimetry of proton and carbon ions
- 2014
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 41:8, s. 239-250
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate microdosimetry properties of 160 MeV/u protons and 290 MeV/u C-12 ion beams in small volumes of diameters 10-100 nm. Methods: Energy distributions of primary particles and nuclear fragments in the beams were calculated from simulations with the general purpose code SHIELD-HIT, while energy depositions by monoenergetic ions in nanometer volumes were obtained from the event-by-event Monte Carlo track structure ion code PITS99 coupled with the electron track structure code KURBUC. Results: The results are presented for frequencies of energy depositions in cylindrical targets of diameters 10-100 nm, dose distributions (y) over bar (D) in lineal energy y, and dose-mean lineal energies YD For monoenergetic ions, the hp was found to increase with an increasing target size for high-linear energy transfer (LET) ions, but decrease with an increasing target size for low-LET ions. Compared to the depth dose profile of the ion beams, the maximum of the hp depth profile for the 160 MeV proton beam was located at similar to 0.5 cm behind the Bragg peak maximum, while the PD peak of the 290 MeV/u C-12 beam coincided well with the peak of the absorbed dose profile. Differences between the (y) over bar (D) and dose-averaged linear energy transfer (LETD) were large in the proton beam for both target volumes studied, and in the C-12 beam for the 10 nm diameter cylindrical volumes. The (y) over bar (D) determined for 100 run diameter cylindrical volumes in the C-12 beam was approximately equal to the LETD. The contributions from secondary particles to the (y) over bar (D) of the beams are presented, including the contributions from secondary protons in the proton beam and from fragments with atomic number Z = 1-6 in the C-12 beam. Conclusions: The present investigation provides an insight into differences in energy depositions in subcellular-size volumes when irradiated by proton and carbon ion beams. The results are useful for characterizing ion beams of practical importance for biophysical modeling of radiation-induced DNA damage response and repair in the depth profiles of protons and carbon ions used in radiotherapy.
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| 8. |
- Liamsuwan, Thiansin, 1984-, et al.
(författare)
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Physical and biophysical properties of proton tracks of energies 1 keV to 300 MeV in water
- 2011
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 87:2, s. 141-160
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Tidskriftsartikel (refereegranskat)abstract
- Materials and methods: aEuro integral We present model calculations for cross sections and methods for simulations of full-slowing-down proton tracks. Protons and electrons were followed interaction-by-interaction to cut-off energies, considering elastic scattering, ionisation, excitation, and charge-transfer. Results: aEuro integral Model calculations are presented for singly differential and total cross sections, and path lengths and stopping powers as a measure of the code evaluation. Depth-dose distributions for 160 MeV protons are compared with experimental data. Frequencies of energy loss by electron interactions increase from similar to 3%% for 10 keV to similar to 77%% for 300 MeV protons, and electrons deposit aEuroS > 70%% of the dose in 160 MeV tracks. From microdosimetry calculations, 1 MeV protons were found to be more effective than 5--300 MeV in energy depositions greater than 25, 50, and 500 eV in cylinders of diameters and lengths 2, 10, and 100 nm, respectively. For lower-energy depositions, higher-energy protons are more effective. Decreasing the target size leads to the reduction of frequency- and dose-mean lineal energies for protons < 1 MeV, and conversely for higher-energy protons. Conclusions: aEuro integral Descriptions of proton tracks at molecular levels facilitate investigations of track properties, energy loss, and microdosimetric parameters for radiation biophysics, radiation therapy, and space radiation research.
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| 9. |
- Liljequist, David, et al.
(författare)
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Elastic scattering cross section models used for Monte Carlo simulation of electron tracks in media of biological and medical interest
- 2012
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 88:1-2, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Elastic scattering is important for the spatial distribution of electrons penetrating matter, and thus for the distribution of deposited energy and DNA damage. Scattering media of interest are in particular liquid and gaseous water and gaseous nitrogen. The former are used as surrogates for tissue and cell environments (since more than 70% of the cell consists of water), while cross section data for nitrogen have been scaled and used as input in Monte Carlo (MC) codes simulating scattering in biologically relevant media. A short review is given of electron elastic scattering cross section models used in a biological and medical context and their experimental and theoretical background.Conclusions: Adequate theories and models exist for calculating elastic electron scattering in gaseous nitrogen and gaseous water (i.e., by free molecules) down to electron energies well below 100 eV. However, elastic electron scattering in liquid water at such low energies is apparently uncertain and not well understood. Further studies in the case of liquid water are thus motivated due to its biological importance.
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| 10. |
- Lindborg, Lennart, et al.
(författare)
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Nanodosimetry and RBE values in radiotherapy
- 2015
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Ingår i: Radiation Protection Dosimetry. - : OXFORD UNIV PRESS. - 0144-8420 .- 1742-3406. ; 166:1-4, s. 339-342
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper, the authors reported that the dose mean lineal energy, (y) over bar (D) in a volume of about 10-15 nm is approximately proportional to the alpha-parameter in the linear-quadratic relation used in fractionated radiotherapy in both low- and high-LET beams. This was concluded after analyses of reported radiation weighting factors, W-isoE (clinical RBE values), and (y) over bar (D) values in a large range of volumes. Usually, microdosimetry measurements in the nanometer range are difficult; therefore, model calculations become necessary. In this paper, the authors discuss the calculation method. A combination of condensed history Monte Carlo and track structure techniques for calculation of mean lineal energy values turned out to be quite useful. Briefly, the method consists in weighting the relative dose fractions of the primary and secondary charged particles with their respective energy-dependent dose mean lineal energies. The latter were obtained using a large database of Monte Carlo track structure calculations.
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