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Dosimetry In-vivo Dosimetry
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by tcc, 2011-04-21 18:51, 人氣(5133)
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1.
In-vivo dosimetryKrishna Komanduri PhDDirector of PhysicsCancer Treatment Services International
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Definition of the Problem
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For High-energy electrons Surface dose Target dose Total skin irradiation
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Practical consequencesThermal fading should be evaluated on each individual reader with the TLmaterial which is intended to be used. It should be approximately 1% per month, orless, for the different preparations of LiF when readout and annealing conditions arereached. For Li2B4O7 it varies from 0,5 to 1% per week depending upon the doping.When a long delay separates irradiation from readout, a fading correction maybe necessary.TL materials which show a standard deviation higher than + 2 % are either ofpoor quality or are not correctly handled and read out. They should not be used for invivo measurements or the handling procedure should be improved.
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Practical consequencesThermal fading should be evaluated on each individual reader with the TLmaterial which is intended to be used. It should be approximately 1% per month, orless, for the different preparations of LiF when readout and annealing conditions arereached. For Li2B4O7 it varies from 0,5 to 1% per week depending upon the doping.When a long delay separates irradiation from readout, a fading correction maybe necessary.TL materials which show a standard deviation higher than + 2 % are either ofpoor quality or are not correctly handled and read out. They should not be used for invivo measurements or the handling procedure should be improved.
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Practical consequencesIn practice it is recommended to use TL dosimeters in the region where theirresponse is proportional to the dose received (linear region). When it is not the case, a correction should be applied to the signal from a curve established with the TL material as well as the reader used (and not from a published curve because the readout parameters may have an influence on its shape). This curve should be checked periodically.It can be introduced in the computer associated with some automatic readout systems, thus allowing an automatic correction of the readouts. TL dosimeters should not be used in the sub linear region approaching saturation.
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Geometrical Configurations:
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Diodes …contd Influence of temperatureInfluence of energy Photon energy Electron energy Directional effect
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Clinical use Calibration factors of a diode Entrance dose calibration factor Exit dose calibration factor Use of a diode in clinical conditions
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(1). Entrance Calibration Factor, Fcal,en
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(2). Exit Calibration Factor, Fcal,ex
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Beam dependent correction factors
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Intrinsic correction factors
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Optional study:
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Practical consequences:Diodes and associated electrometer should have a drift less than 1% in the time range encountered in practice. Equipment falling outside this range should notbe accepted.
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MOSFET dosimeters
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Systematic Problem with QA
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Workflow -- Visualize, Verify, Validate
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