Wall correction factors, , for thimble ionization chambers
- 30 January 2006
- journal article
- Published by Wiley in Medical Physics
- Vol. 33 (2), 455-464
- https://doi.org/10.1118/1.2161403
Abstract
The EGSnrc Monte Carlo user-code CSnrc is used to calculate wall correction factors, Pwall, for thimble ionization chambers in photon and electron beams. CSnrc calculated values of Pwall give closer agreement with previous experimental results than do the values from the standard formalism used in current dosimetry protocols. A set of Pwall 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 6 MV. 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 Pwal1 correction itself. In electron beams, where dosimetry protocols assume a wall correction of unity, CSnrc calculations show Pwall values of up to 0.6% at the reference depth, depending on the wall material. Pwall 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 0.5 cm and R50 in a 6 MeV electron beam.Keywords
This publication has 26 references indexed in Scilit:
- Monte Carlo calculation of nine megavoltage photon beam spectra using the BEAM codeMedical Physics, 2002
- Effect of size and composition of the central electrode on the response of cylindrical ionization chambers in high-energy photon and electron beamsPhysics in Medicine & Biology, 1993
- The effect of waterproofing sleeves on ionization chamber responsePhysics in Medicine & Biology, 1992
- Implication of electron backscattering for electron dosimetryPhysics in Medicine & Biology, 1991
- Wall attenuation and scatter corrections for ion chambers: measurements versus calculationsPhysics in Medicine & Biology, 1990
- Effective mass stopping power ratio in photon dosimetryPhysics in Medicine & Biology, 1979
- A proposal concerning the absorbed dose conversion factorPhysics in Medicine & Biology, 1978
- Ionization Chamber Dosimetry for Photon and Electron BeamsActa Radiologica: Therapy, Physics, Biology, 1977
- Photon cross sections from 1 keV to 100 MeV for elements Z=1 to Z=100Atomic Data and Nuclear Data Tables, 1970