Effective point of measurement of thimble ion chambers in megavoltage photon beams
- 4 December 2009
- journal article
- research article
- Published by Wiley in Medical Physics
- Vol. 37 (1), 96-107
- https://doi.org/10.1118/1.3266750
Abstract
Purpose: Determine the effective point of measurement (EPOM) of 12 thimble ion chambers, including miniature chambers and three models widely used for clinical reference dosimetry. The EPOM is the point at which the measured dose would arise in the measurement medium in the absence of the probe: For cylindrical chambers, it is shifted upstream relative to the central axis of the chamber. Although current dosimetry protocols prescribe a blanket upstream EPOM shift of 0.6r, with r as the chamber cavity radius, it has been shown in recent years that the EPOM does, in fact, depend on every detail of the chamber design and on the beam characteristics. In the wake of this finding, the authors undertake a comprehensive study of the EPOM for a series of chambers in water.Peer reviewed: YesNRC publication: YeKeywords
Funding Information
- U.S. Nuclear Regulatory Commission
This publication has 19 references indexed in Scilit:
- Efficiency improvements for ion chamber calculations in high energy photon beamsMedical Physics, 2008
- The effective point of measurement of ionization chambers and the build‐up anomaly in MV x‐ray beamsMedical Physics, 2008
- A “HOWFARLESS” option to increase efficiency of homogeneous phantom calculations with DOSXYZnrcMedical Physics, 2007
- On the effective point of measurement in megavoltage photon beamsMedical Physics, 2006
- Influence of ion chamber response on in-air profile measurements in megavoltage photon beamsMedical Physics, 2005
- Large efficiency improvements in BEAMnrc using directional bremsstrahlung splittingMedical Physics, 2004
- Accurate condensed history Monte Carlo simulation of electron transport. I. EGSnrc, the new EGS4 versionMedical Physics, 2000
- AAPM's TG‐51 protocol for clinical reference dosimetry of high‐energy photon and electron beamsMedical Physics, 1999
- Introduction to Radiological Physics and Radiation DosimetryPublished by Wiley ,1986
- Analytic and graphical methods for assigning errors to parameters in non-linear least squares fittingNuclear Instruments and Methods, 1975