Program Information
Comparison Between a PTW MicroDiamond Dosimeter and a Markus Chamber in a 62 MeV/n Carbon Ion Beam
S Rossomme1*, J Hopfgartner2 , A Delor3 , S Vynckier1,3 , H Palmans2,4 , (1) Universite catholique de Louvain, Brussels, Belgium, (2) EBG MedAustron GmbH, Wiener Neustadt, Vienna, (3) Cliniques universitaires Saint-Luc, Brussels, Belgium, (4) National Physical Laboratory, Teddington, UK,
Presentations
SU-E-T-198 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To investigate the linear energy transfer (LET) dependence of a PTW Freiburg microDiamond dosimeter, we compared its response to the response of a plane-parallel Markus chamber in a 62 MeV/n mono-energetic carbon ion beam.
Methods: The response of both detectors has been studied as a function of depth in graphite by adding or removing graphite plates in front of the detectors. To account for fluctuations of the beam, we used two setups with different monitor chambers. The depth of the effective point of measurement of both detectors has been converted into a graphite equivalent depth using ICRU Report 73 data. As recommended by IAEA TRS-398, the response of the Markus chamber has been corrected for temperature, pressure, polarity effects and ion recombination. The latter required an additional experiment; to quantify the effect of volume recombination and initial recombination, measurements have been performed at different voltages and different dose rates.
Results: As expected, the dominant process leading to ion recombination for carbon ion beam is the initial recombination. At the entrance, the ion recombination correction equals 1.1% and the value is approximately constant in the plateau region. Due to the increase of the LET in the Bragg peak region, we observe a strong increase of the ion recombination correction, up to 6.1% at the distal edge. Comparison between the microDiamond response and the Markus chamber response shows good agreement in the plateau region. However, we observe a 13.6% under response of the microDiamond in the Bragg peak.
Conclusion: Increasing between 1% and 6%, the depth dependent ion recombination correction has to be applied to the Markus response. The comparison between the microDiamond and the Markus chamber indicates that there is an under-response of the microDiamond in the vicinity of the Bragg peak due to the increased LET.
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