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The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
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.
Keyword [en]
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
Identifiers
URN: urn:nbn:se:su:diva-6687ISBN: 91-7155-391-6 (print)OAI: oai:DiVA.org:su-6687DiVA: diva2:196874
Public defence
2007-03-23, föreläsningssalen, Radiumhemmet, Karolinska universitetssjukhuset, Solna, 10:00
Opponent
Supervisors
Available from: 2007-03-01 Created: 2007-02-26Bibliographically approved
List of papers
1. The response of the Sievert instrument in neutron beams up to 180 MeV
Open this publication in new window or tab >>The response of the Sievert instrument in neutron beams up to 180 MeV
2001 In: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 94, no 3, 227-232 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24146 (URN)
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26Bibliographically approved
2. Photon and neutron dose discrimination using low pressure proportional counters with graphite and A150 walls
Open this publication in new window or tab >>Photon and neutron dose discrimination using low pressure proportional counters with graphite and A150 walls
2007 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 125, no 1-4, 314-317 p.Article in journal (Refereed) Published
Abstract [en]

A graphite-walled proportional counter with low neutron sensitivity was used in combination with a tissue-equivalent proportional counter (TEPC) to separate the photon and neutron components in mixed radiation fields. Monte Carlo (MCNP4C) simulations of the photon and neutron responses of the two detectors were done to obtain correction factors for the sensitivity differences. In an alternative method the radiation components were determined using constant-yD-values for typical photon and neutron energy distributions. The results show no significant difference between the two methods and the measured neutron dose-equivalent agrees within ±50% with Bonner sphere determined values. The experimental data were obtained in measurement campaigns organised within the EVIDOS-project.

Place, publisher, year, edition, pages
Oxford University Press, 2007
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-24147 (URN)10.1093/rpd/ncm162 (DOI)
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26 Last updated: 2011-01-18Bibliographically approved
3. Cosmic radiation measurements on-board aircraft with the variance method
Open this publication in new window or tab >>Cosmic radiation measurements on-board aircraft with the variance method
2001 In: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 93, no 3, 197-205 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24148 (URN)
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26Bibliographically approved
4. A comparison of ambient dose equivalent meters and dose calculations at constant flight conditions
Open this publication in new window or tab >>A comparison of ambient dose equivalent meters and dose calculations at constant flight conditions
Show others...
2007 (English)In: Radiation Measurements, ISSN 1350-4487, E-ISSN 1879-0925, Vol. 42, no 3, 323-333 p.Article in journal (Refereed) Published
Abstract [en]

Ambient dose-equivalent results from an in-flight comparison between different tissue-equivalent proportional counters and silicon diode spectrometers from seven European institutes are presented and compared with calculations using the EPCARD computer program. The measurements were performed on 40 000 and 32 000 ft in narrow target areas at latitudes N57 and N42. Keeping the altitude and geographic position almost constant provided unique conditions for comparisons.

The different measuring systems as well as the calculations are in remarkably good agreement, with an average standard deviation in the ambient dose equivalent between 6% and 21%. The ratio between calculated and measured ambient dose-equivalent rates varies between 0.91 and 1.09, with an average of 1.00±0.08 (1s). Nevertheless some systematic differences in the experimentally determined ambient dose equivalent and its low-LET and high-LET components are noticed and discussed. It is concluded that the standard deviation between different instruments can through optimization and harmonization of the calibration procedures be reduced by up to a factor of two.

Place, publisher, year, edition, pages
Elsevier Ltd, 2007
Keyword
Aircrew exposure; Cosmic radiation; TEPC; Microdosimetry; Variance–covariance method
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-24149 (URN)10.1016/j.radmeas.2006.12.011 (DOI)
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26 Last updated: 2017-12-13Bibliographically approved
5. Nanodosimetry in a clinical neutron therapy beam using the variance-covariance method and Monte Carlo simulations
Open this publication in new window or tab >>Nanodosimetry in a clinical neutron therapy beam using the variance-covariance method and Monte Carlo simulations
Show others...
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
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-24150 (URN)10.1088/0031-9155/52/16/016 (DOI)000249089700016 ()
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26 Last updated: 2017-12-13Bibliographically approved

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