Wall correction factors, , for thimble ionization chambers

Medical Physics - Tập 33 Số 2 - Trang 455-464 - 2006
Lesley Buckley1,2, D. W. O. Rogers3,2
1Also at the National Research Council of Canada, Ottawa, ON K1A 0R6, Canada.
2Ottawa-Carleton Institute of Physics, Carleton University, Ottawa, K1S 5B6, Canada
3Electronic mail: [email protected]

Tóm tắt

The EGSnrc Monte Carlo user‐code CSnrc is used to calculate wall correction factors, , for thimble ionization chambers in photon and electron beams. CSnrc calculated values of give closer agreement with previous experimental results than do the values from the standard formalism used in current dosimetry protocols. A set of values, computed at the reference depth in water, is presented for several commonly used thimble chambers. These values differ from the commonly used values by up to 0.8% for megavoltage photon beams, particularly for nominal beam energies below . The sleeve effect, which is not currently taken into account by the TG‐51 dosimetry protocol, is computed to be up to 0.3% and is in some cases larger than the correction itself. In electron beams, where dosimetry protocols assume a wall correction of unity, CSnrc calculations show values of up to 0.6% at the reference depth, depending on the wall material. is shown to be sensitive to the depth of measurement, varying by 2.5% for a graphite‐walled cylindrical Farmer‐like chamber between a depth of and in a electron beam.

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See EPAPS Document No.E‐MPHYA6‐33‐010602for additional figures showing the wall correction factor in high energy photon and electron beams. This document can be reached via a direct link in the online article's HTML reference section or via the EPAPS homepage (http://www.aip.org/pubservs/epaps.html).

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Medical Physics

Tập 33 Số 2

455-464

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