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Radial secondary electron dose profiles and biological effects in light-ion beams based on analytical and Monte Carlo calculations using distorted wave cross sections
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).
2008 (English)In: Radiation Research, ISSN 0033-7587, Vol. 170, no 1, 83-92 p.Article in journal (Refereed) Published
Abstract [en]

To speed up dose calculation, an analytical pencil-beam method has been developed to calculate the mean radial dose distributions due to secondary electrons that are set in motion by light ions in water. For comparison, radial dose profiles calculated using a Monte Carlo technique have also been determined. An accurate comparison of the resulting radial dose profiles of the Bragg peak for (1)H(+), (4)He(2+) and (6)Li(3+) ions has been performed. The double differential cross sections for secondary electron production were calculated using the continuous distorted wave-eikonal initial state method (CDW-EIS). For the secondary electrons that are generated, the radial dose distribution for the analytical case is based on the generalized Gaussian pencil-beam method and the central axis depth-dose distributions are calculated using the Monte Carlo code PENELOPE. In the Monte Carlo case, the PENELOPE code was used to calculate the whole radial dose profile based on CDW data. The present pencil-beam and Monte Carlo calculations agree well at all radii. A radial dose profile that is shallower at small radii and steeper at large radii than the conventional 1/r(2) is clearly seen with both the Monte Carlo and pencil-beam methods. As expected, since the projectile velocities are the same, the dose profiles of Bragg-peak ions of 0.5 MeV (1)H(+), 2 MeV (4)He(2+) and 3 MeV (6)Li(3+) are almost the same, with about 30% more delta electrons in the sub keV range from (4)He(2+)and (6)Li(3+) compared to (1)H(+). A similar behavior is also seen for 1 MeV (1)H(+), 4 MeV (4)He(2+) and 6 MeV (6)Li(3+), all classically expected to have the same secondary electron cross sections. The results are promising and indicate a fast and accurate way of calculating the mean radial dose profile.

Place, publisher, year, edition, pages
2008. Vol. 170, no 1, 83-92 p.
Keyword [en]
Electrons, Ions, Light, Monte Carlo Method
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-17677DOI: 10.1667/RR0961.1ISI: 000257298100009PubMedID: 18582149OAI: oai:DiVA.org:su-17677DiVA: diva2:184198
Available from: 2009-01-19 Created: 2009-01-19 Last updated: 2012-03-22Bibliographically 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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