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14 Cards in this Set
- Front
- Back
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What is a phantom
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-A tissue-equivalent material, usually large in volume to provide for full scatter for the given beam.
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What are phantoms used for?
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-used to predict dose distributions
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What are basic dose distributions usually measured in?
-this material closely approsimates the radiation absorption and scattering of ____ and other ______ _____. |
-a WATER phantom
-muscle -soft tissue. |
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The percentage depth dose (increases/decreases) with beam energy?
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-increases
-higher energy beams have greater penetrating power. |
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The percentage depth dose (increases/decreases) with depth beyond the depth of maximum dose.
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-decreases
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HOWEVER,
there is an initial buildup of dose that becomes more and more pronounced as the energy is ________. |
increased
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The percent depth dose _______ with increasing field size.
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increases
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The field size dependence of percent depth dose is (more/less) pronounced for the higher-energy than for the lower-energy beams.
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-less
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The increase in percent depth dose caused by increase in field size depends on _______.
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-beam quality
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Percent depth dose _______ with SSD because of the effects of ____ ______ _____.
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-increase
-inverse square law |
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Define tissue air ratio
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the ratio of the dose at a given point in the phantom to the dose in free space at the same point.
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-for a given quality beam, TAR depends on ____ and _____ at that depth.
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-depth
-field size |
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TAR involves both ___ and ___ and is (independent/dependent) of the source distance
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-primary and scatter
-independent |
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TAR varies with what 3 things
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enery, depth, and field size
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