PMID: 9434981Jan 22, 1998Paper

Differences in wedge factor determination in air using a PMMA mini-phantom or a brass build-up cap

Medical Physics
S HeukelomB J Mijnheer

Abstract

The head scatter dose contribution to the output of a treatment machine has been determined for an open and wedged 60Co gamma-ray beam and for open and wedged x-ray beams of 4, 8, and 16 MV. From those data wedge factor values "in air" have been deduced, expressed as the ratio of the dose to water, measured in air, for the situation with and without wedge, for the same number of monitor units (or treatment time for 60Co). The measurements have been performed using a polymethyl-metacrylate (PMMA) and a graphite-walled ionization chamber inserted in a brass build-up cap and in a PMMA mini-phantom, respectively. Absolute wedge factor values deduced with both detector systems and based on the ratio of ionization chamber readings, differ for the investigated photon beams, up to 3.5% for the 4 MV x-ray beam. The deviations results from the difference in composition between the detector materials and water and can be taken into account by conversion of the ionization chamber readings for both the open and wedged photon beams to the absorbed dose to water. For the brass build-up cap detector system the ratio of the conversion factors for the wedged and open beam changes the ratio of the ionization chamber readings up to about 3.6% for ...Continue Reading

References

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Jan 1, 1994·Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology·S HeukelomB J Mijnheer
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Citations

Aug 22, 2001·Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology·D GeorgJ Venselaar
Jul 1, 2008·Journal of Medical Physics·S Senthilkumar, V Ramakrishnan
Nov 7, 2007·Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology·Carolyn McKerracher, David I Thwaites
Dec 10, 2009·Medical Physics·Timothy C ZhuUNKNOWN AAPM Therapy Physics Committee Task Group 74
Feb 2, 2013·Technology in Cancer Research & Treatment·Murugan AppasamyRamasubramanian Velayudham
Dec 10, 1999·Physics in Medicine and Biology·A Ahnesjö, M M Aspradakis

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