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Nanodosimetry in a clinical neutron therapy beam using the variance-covariance method and Monte Carlo simulations
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
Stockholm University, Faculty of Science, Department of Physics.
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2007 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 52, no 16, 4953- p.Article in journal (Refereed) Published
Abstract [en]

Nanodosimetric single-event distributions or their mean values may contribute to a better understanding of how radiation induced biological damages are produced. They may also provide means for radiation quality characterization in therapy beams. Experimental nanodosimetry is however technically challenging and Monte Carlo simulations are valuable as a complementary tool for such investigations. The dose-mean lineal energy was determined in a therapeutic p(65)+Be neutron beam and in a 60Co γ beam using low-pressure gas detectors and the variance-covariance method. The neutron beam was simulated using the condensed history Monte Carlo codes MCNPX and SHIELD-HIT. The dose-mean lineal energy was calculated using the simulated dose and fluence spectra together with published data from track-structure simulations. A comparison between simulated and measured results revealed some systematic differences and different dependencies on the simulated object size. The results show that both experimental and theoretical approaches are needed for an accurate dosimetry in the nanometer region. In line with previously reported results, the dose-mean lineal energy determined at 10 nm was shown to be related to clinical RBE values in the neutron beam and in a simulated 175 MeV proton beam as well. 

Place, publisher, year, edition, pages
IOP , 2007. Vol. 52, no 16, 4953- p.
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-24150DOI: 10.1088/0031-9155/52/16/016ISI: 000249089700016OAI: diva2:196873
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26 Last updated: 2010-09-30Bibliographically approved
In thesis
1. The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy
Open this publication in new window or tab >>The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radiation quality is described by the RBE (relative biological effectiveness) that varies with the ionizing ability of the radiation. Microdosimetric quantities describe distributions of energy imparted to small volumes and can be related to RBE. This has made microdosimetry a powerful tool for radiation quality determinations in both radiation protection and radiation therapy. The variance-covariance method determines the dose-average of the distributions and has traditionally been used with two detectors to correct for beam intensity variations. Methods to separate dose components in mixed radiation fields and to correct for beam variations using only one detector have been developed in this thesis. Quality factor relations have been optimized for different neutron energies, and a new algorithm that takes single energy deposition events from densely ionizing radiation into account has been formulated. The variance-covariance technique and the new methodology have been shown to work well in the cosmic radiation field onboard aircraft, in the mixed photon and neutron fields in the nuclear industry and in pulsed fields around accelerators.

The method has also been used for radiation quality characterization in therapy beams. The biological damage is related to track-structure and ionization clusters and requires descriptions of the energy depositions in nanometre sized volumes. It was shown that both measurements and Monte Carlo simulation (condensed history and track-structure) are needed for a reliable nanodosimetric beam characterization. The combined experimental and simulated results indicate that the dose-mean of the energy imparted to an object in the nanometre region is related to the clinical RBE in neutron, proton and photon beams. The results suggest that the variance-covariance technique and the dose-average of the microdosimetric quantities could be well suited for describing radiation quality also in therapy beams.

Place, publisher, year, edition, pages
Stockholm: Medicinsk strålningsfysik (tills m KI), 2007. 146 p.
ionizing radiation, radiation quality, radiation protection, radiation therapy, microdosimetry, nanodosimetry, variance-covariance method
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Radiation Physics
urn:nbn:se:su:diva-6687 (URN)91-7155-391-6 (ISBN)
Public defence
2007-03-23, föreläsningssalen, Radiumhemmet, Karolinska universitetssjukhuset, Solna, 10:00
Available from: 2007-03-01 Created: 2007-02-26Bibliographically approved

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Gudowska, Irena
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