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A Monte Carlo program for the analysis of low-energy electron tracks in liquid water
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
2011 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 56, no 7, 1985-2003 p.Article in journal (Refereed) Published
Abstract [en]

A Monte Carlo code for the event-by-event simulation of electron transport in liquid water is presented. The code, written in C++, can accommodate different interaction models. Currently it implements cross sections for ionizing collisions calculated with the model developed by Dingfelder et al (1998 Radiat. Phys. Chem. 53 1–18, 2008 Radiat. Res. 169 584–94) and cross sections for elastic scattering computed within the static-exchange approximation (Salvat et al 2005 Comput. Phys. Commun. 165 157–90). The latter cross sections coincide with those recommended in ICRU Report 77 (2007). Other included interaction mechanisms are excitation by electron impact and dissociative attachment. The main characteristics of the code are summarized. Various track penetration parameters, including the detour factor, are defined as useful tools to quantify the geometrical extent of electron tracks in liquid water. Results obtained with the present microdosimetry code are given in the form of probability density functions for initial electron kinetic energies ranging from 0.1 to 10 keV. The sensitivity of the simulated distributions to the choice of alternative physics models has been briefly explored. The discrepancies with equivalent simulations reported by Wilson et al (2004 Radiat. Res. 161 591–6) stem from the adopted cross sections for elastic scattering, which determine largely the spatial evolution of low-energy electron tracks.

Place, publisher, year, edition, pages
2011. Vol. 56, no 7, 1985-2003 p.
Keyword [en]
Monte Carlo track structure calculations, Cross sections
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-74718DOI: 10.1088/0031-9155/56/7/005OAI: oai:DiVA.org:su-74718DiVA: diva2:511522
Available from: 2012-03-21 Created: 2012-03-21 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Modeling of dose and sensitivity heterogeneities in radiation therapy
Open this publication in new window or tab >>Modeling of dose and sensitivity heterogeneities in radiation therapy
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increased interest in the use of light ion therapy is due to the high dose conformity to the target and the dense energy deposition along the tracks resulting in increased relative biological effectiveness compared to conventional radiation therapy. In spite of the good clinical experience, fundamental research on the characteristics of the ion beams is still needed in order to be able to fully explore their use. Therefore, a Monte Carlo track structure code, KITrack, simulating the transport of electrons in liquid water, has been developed and used for calculation of parameters of interest for beam characterization. The influence of the choice of the cross sections for the physical processes on the electron tracks has also been explored. As an alternative to Monte Carlo calculations a semi-analytical approach to calculate the radial dose distribution from ions, has been derived and validated.

In advanced radiation therapy, accurate characterization of the beams has to be complemented by comprehensive radiobiological models, which relate the dose deposition into the cells to the outcome of the treatment. The second part of the study has therefore explored the influence of heterogeneity in the dose deposition into the cells as well as the heterogeneity in the cells sensitivity to radiation on the probability of controlling the tumor. Analytical expressions for tumor control probability including heterogeneous dose depositions or variation of radiation sensitivity of cells and tumors have been derived and validated with numerical simulations. The more realistic case of a combination of these effects has also been explored through numerical simulations.

The MC code KITrack has evolved into an extremely useful tool for beam characterization. The tumor control probability, given by the analytical derived expression, can help improve radiation therapy. A novel anisotropy index has been proposed. It is a measure of the absence of isotropy and provides deeper understanding of the relationship between beam quality and biological effects.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2012. 93 p.
Keyword
Monte Carlo simulations, Tumor control probability, Modeling, Beam characterization
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-74719 (URN)978-91-7447-473-2 (ISBN)
Public defence
2012-05-04, the lecture hall, Radiumhemmet, Karolinska universitetssjukhuset, Solna, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2012-04-12 Created: 2012-03-21 Last updated: 2014-04-16Bibliographically approved

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