PMID: 15377097Sep 21, 2004Paper

Compensator thickness verification using an a-Si EPID

Medical Physics
Geetha V Menon, Ron S Sloboda

Abstract

Electronic portal imaging devices (EPIDs) are being increasingly employed to make therapy verification and dose measurements in the clinic. In this work, we investigate the use of an amorphous silicon (a-Si) EPID to verify the accuracy of compensator fabrication and mounting. Compensator thickness estimates on a two-dimensional grid were calculated from the primary component of transmission obtained by subtracting a modeled scatter component from the total transmission measured with the EPID. The primary component was related to the thickness via an exponential relation that includes beam hardening. Implementation of the method involved determination of: (i) a calibration curve relating EPID pixel values to energy fluence for open and attenuated fields, which was found to be linear for open fields but to have a small quadratic component for attenuated beams; (ii) EPID scatter factors to account for field size effects, which exhibited a small dependence on compensator thickness and field size; (iii) the attenuation coefficient of the steel shot compensator material, which varied slightly with off-axis distance and field size, and (iv) an analytical model to predict scatter from the compensator, which was calculated to be <4% at ...Continue Reading

References

May 1, 1982·Medical Physics·A L Boyer
Feb 1, 1997·Medical Physics·M K YuB Murray
Apr 11, 2000·Medical Physics·L SpiesT Bortfeld
Aug 9, 2003·Medical Physics·Geetha V Menon, Ron S Sloboda
Jun 1, 1959·The British Journal of Radiology·F ELLISR OLIVER
Mar 17, 2004·Medical Dosimetry : Official Journal of the American Association of Medical Dosimetrists·Geetha V Menon, Ron S Sloboda
Jun 1, 1950·The British Journal of Radiology·M J DAY

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Citations

Jun 22, 2013·Physica Medica : PM : an International Journal Devoted to the Applications of Physics to Medicine and Biology : Official Journal of the Italian Association of Biomedical Physics (AIFB)·Guang-hua JinXiao-wei Liu
Nov 4, 2005·Medical Physics·Todd PawlickiArthur L Boyer
Oct 30, 2010·Physics in Medicine and Biology·T KairnJ V Trapp

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