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Cross sections for bare and dressed carbon ions in water and neon
Karolinska Institutet, Institutionen för onkologi-patologi .
Karolinska Institutet, Institutionen för onkologi-patologi .
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.

Place, publisher, year, edition, pages
2013. Vol. 58, 641-672 p.
Keyword [en]
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: urn:nbn:se:su:diva-81452DOI: 10.1088/0031-9155/58/3/641OAI: oai:DiVA.org:su-81452DiVA: diva2:561737
Available from: 2012-10-21 Created: 2012-10-21 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Development of Monte Carlo track structure simulations for protons and carbon ions in water
Open this publication in new window or tab >>Development of Monte Carlo track structure simulations for protons and carbon ions in water
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
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:nbn:se:su:diva-81461 (URN)978-91-7447-591-3 (ISBN)
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

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