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Development of Monte Carlo track structure simulations for protons and carbon ions in water
Stockholm University, Faculty of Science, Department of Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2012. , 107 p.
Keyword [en]
Radiation track structure, Monte Carlo simulations, interaction cross sections, classical trajectory Monte Carlo (CTMC) method, microdosimetry, ion beams
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-81461ISBN: 978-91-7447-591-3 (print)OAI: oai:DiVA.org:su-81461DiVA: diva2:561741
Public defence
2012-11-30, Rondrum 1, Building A6, Floor 1 (A6:01), Nuclear Medicine Department, Karolinska University Hospital, Solna, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.

 

Available from: 2012-11-08 Created: 2012-10-21 Last updated: 2017-11-22Bibliographically approved
List of papers
1. Physical and biophysical properties of proton tracks of energies 1 keV to 300 MeV in water
Open this publication in new window or tab >>Physical and biophysical properties of proton tracks of energies 1 keV to 300 MeV in water
2011 (English)In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 87, no 2, 141-160 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Monte Carlo simulation, track structure, proton, cross sections, microdosimetry
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-81449 (URN)10.3109/09553002.2010.518204 (DOI)000287087100003 ()
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07
2. A model of carbon ion interactions in water using the classical trajectory Monte Carlo method
Open this publication in new window or tab >>A model of carbon ion interactions in water using the classical trajectory Monte Carlo method
2011 (English)In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 143, no 2-4, 152-155 p.Article in journal (Refereed) Published
Abstract [en]

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.                

Keyword
Carbon ions, charge transfer, interaction cross sections, classical trajectory Monte Carlo (CTMC)
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-81459 (URN)10.1093/rpd/ncq395 (DOI)000288022300005 ()
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07Bibliographically approved
3. An energy-loss model for low- and intermediate-energy carbon projectiles in water
Open this publication in new window or tab >>An energy-loss model for low- and intermediate-energy carbon projectiles in water
2012 (English)In: International Journal of Radiation Biology, ISSN 0955-3002, E-ISSN 1362-3095, Vol. 88, no 1-2, 45-49 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Carbon ions, charge transfer, interaction cross sections, CTMC, equilibrium charge, stopping cross sections
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-81451 (URN)10.3109/09553002.2011.620061 (DOI)000298666000008 ()
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07Bibliographically approved
4. Cross sections for bare and dressed carbon ions in water and neon
Open this publication in new window or tab >>Cross sections for bare and dressed carbon ions in water and neon
2013 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, 641-672 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
CTMC, Carbon ions, Cross sections, Charge transfer, Stopping power, Track structure
National Category
Atom and Molecular Physics and Optics
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-81452 (URN)10.1088/0031-9155/58/3/641 (DOI)
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07Bibliographically approved
5. 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
Open this publication in new window or tab >>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 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 3, 673-702 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Track structure, Monte Carlo simulations, carbon ions, Bragg peak, SOBP, dosimetry, LET, CTMC
National Category
Physical Sciences Other Computer and Information Science
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-81453 (URN)10.1088/0031-9155/58/3/673 (DOI)
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07Bibliographically approved

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