Determination of relative ion chamber calibration coefficients from depth-ionization measurements in clinical electron beams

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DOIResolve DOI: http://doi.org/10.1088/0031-9155/59/19/5953
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TypeArticle
Journal titlePhysics in Medicine and Biology
ISSN0031-9155
Volume59
Issue19
Article number5953
Pages59535969; # of pages: 17
SubjectCalibration coefficients; Clinical electron beams; Reference dosimetry; Electron beams
AbstractA method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination.
Publication date
LanguageEnglish
AffiliationMeasurement Science and Standards; National Research Council Canada
Peer reviewedYes
NPARC number21272646
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Record identifier2fd0383c-7ea9-4a5f-a34c-e2231684e08e
Record created2014-12-03
Record modified2016-05-09
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