PMID: 8946375Oct 1, 1996Paper

Dependence of overall correction factor of a cylindrical ionization chamber on field size and depth in medium-energy x-ray beams

Medical Physics
J P Seuntjens, F Verhaegen

Abstract

In this paper we examine the depth and field size dependence of the overall correction factor kch for in-phantom dose determinations in orthovoltage x-ray beams. The overall correction factor is considered to be composed of three contributions, i.e., (1) a contribution from the angular dependence of the chamber response free-in-air, derived based on the measured directional response of the NE2571 for different energies combined with Monte Carlo calculations; (2) a displacement effect and (3) a stem effect, both calculated using the Monte Carlo method for different field sizes and depths. The results show a variation of, at most, 2.2% at the lowest photon energies (29.8-keV average photon energy) when going from 2 cm to 5 cm for a small circular 20-cm2 field. In the medium-energy range (> or = 100 kV), variations are limited to, at most, 1.5% for 120 kV-150 kV when comparing the most extreme variations in field size and depth (i.e., 2-cm depth; 20-cm2 area compared to 5 cm depth; 200-cm2 area). Depth variations most importantly affect the overall correction factor by hardening of the photon fluence spectrum, whereas field diameter variations affect the factor by increase or decrease of contributions of photon scattering. The wor...Continue Reading

Citations

Jul 7, 2001·Medical Physics·C M MaUNKNOWN American Association of Physicists in Medicine
Jan 6, 1999·Medical Physics·C M MaJ P Seuntjens
Oct 4, 2002·Physics in Medicine and Biology·Hugo PalmansHubert Thierens
Sep 26, 1997·Medical Physics·C M Ma, J P Seuntjens
Oct 21, 2005·Physics in Medicine and Biology·R HillC Baldock
Mar 4, 2014·Physics in Medicine and Biology·Robin HillClive Baldock
Aug 12, 1999·Physics in Medicine and Biology·F VerhaegenY Namito
Sep 1, 1996·Physics in Medicine and Biology·A E Nahum
Sep 2, 1998·Physics in Medicine and Biology·N ReynaertH Thierens
Apr 5, 2002·Physics in Medicine and Biology·H M Kramer, B Grosswendt

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