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On the uncertainties of photon mass energy-absorption coefficients and their ratios for radiation dosimetry
Stockholm University, Faculty of Science, Department of Physics.
2012 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 8, 2117-2136 p.Article in journal (Refereed) Published
Abstract [en]

A systematic analysis of the available data has been carried out for mass energy-absorption coefficients and their ratios for air, graphite and water for photon energies between 1 keV and 2 MeV, using representative kilovoltage x-ray spectra for mammography and diagnostic radiology below 100 kV, and for Ir-192 and Co-60 gamma-ray spectra. The aim of this work was to establish 'an envelope of uncertainty' based on the spread of the available data. Type A uncertainties were determined from the results of Monte Carlo (MC) calculations with the PENELOPE and EGSnrc systems, yielding mean values for mu(en)/rho with a given statistical standard uncertainty. Type B estimates were based on two groupings. The first grouping consisted of MC calculations based on a similar implementation but using different data and/or approximations. The second grouping was formed by various datasets, obtained by different authors or methods using the same or different basic data, and with different implementations (analytical, MC-based, or a combination of the two); these datasets were the compilations of NIST, Hubbell, Johns-Cunningham, Attix and Higgins, plus MC calculations with PENELOPE and EGSnrc. The combined standard uncertainty, u(c), for the mu(en)/rho values for the mammography x-ray spectra is 2.5%, decreasing gradually to 1.6% for kilovoltage x-ray spectra up to 100 kV. For Co-60 and Ir-192, u(c) is approximately 0.1%. The Type B uncertainty analysis for the ratios of mu(en)/rho values includes four methods of analysis and concludes that for the present data the assumption that the data interval represents 95% confidence limits is a good compromise. For the mammography x-ray spectra, the combined standard uncertainties of (mu(en)/rho)(graphite,air) and (mu(en)/rho)(graphite,water) are 1.5%, and 0.5% for (mu(en)/rho)(water,air), decreasing gradually down to u(c) = 0.1% for the three mu(en)/rho ratios for the gamma-ray spectra. The present estimates are shown to coincide well with those of Hubbell (1977 Rad. Res. 70 58-81), except for the lowest energy range (radiodiagnostic) where it is concluded that current databases and their systematic analysis represent an improvement over the older Hubbell estimations. The results for (mu(en)/rho)(graphite,air) for the gamma-ray dosimetry range are moderately higher than those of Seltzer and Bergstrom (2005 private communication).

Place, publisher, year, edition, pages
2012. Vol. 57, no 8, 2117-2136 p.
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Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-76050DOI: 10.1088/0031-9155/57/8/2117ISI: 000302567100003OAI: oai:DiVA.org:su-76050DiVA: diva2:525783
Note
3Available from: 2012-05-09 Created: 2012-05-08 Last updated: 2017-12-07Bibliographically approved

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