NDLI: Experimental verification of EGSnrc Monte Carlo calculated ion chamber response in low energy photon beams

Content Provider	IEEE Xplore Digital Library
Author	Borg, J. Kawrakow, I. Rogers, D.W.O. Seuntjens, J.P.
Copyright Year	2000
Description	Author affiliation: Inst. for Nat. Meas. Stand., Nat. Res. Council of Canada, Ottawa, Ont., Canada (Borg, J.)
Abstract	The EGSnrc Monte Carlo system was used to calculate response, defined as the ratio of the dose to the gas in the cavity and air kerma free-in-air at the center of the cavity, normalized at /sup 60/Co. Calculations of the response of a graphite cavity and Exradin A12 air-equivalent plastic chambers were compared with measurements using free-air ionization chambers. For the graphite chamber, the agreement between measured and calculated chamber response diverges up to 8% down to 50 kV. The authors simulated the high-Z contamination, distributed over the inner surface of the wall in the form of iron grains, by introducing an iron ring of 1 /spl mu/m thickness covering 0.45% of the area on the inside wall. These amounts of high-Z contamination are perfectly conceivable considering the machining process of the graphite cavity. Assuming pure C552, for the Exradin A12 the agreement is within 0.5% down to 85 keV but gradually gets worse at lower energies. A mass spectroscopic analysis of C552 showed that the amount of impurities with Z between 10 and 82 amounts to 90 /spl mu/g/g. The calculations with the full composition as resulting from the analysis show agreement within 0.4% down to 70 keV. Below that energy, deviations amount up to 3%. These can be explained by (1) impurities on the inside surface of the wall from the machining process as demonstrated from measurements on other chambers of the same type; (2) accuracy of the spectra used in the calculations; (3) geometrical details of the chamber such as the stem.
Starting Page	3152
Ending Page	3155
File Size	331975
Page Count	4
File Format	PDF
ISBN	0780364651
ISSN	1094687X
DOI	10.1109/IEMBS.2000.901554
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2000-07-23
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Monte Carlo methods Ionization chambers Measurement standards Physics Hospitals Plastics Iron Machining Impurities Calibration
Content Type	Text
Resource Type	Article

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