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34 Cards in this Set
- Front
- Back
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various devices placed in beams pathway |
wedge bolus compensators beam degrader blocks MLC IMRT |
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isodose curve displays... |
the percentage of dose delivered throughout the tissue |
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Dmax |
100% dose dose at max depth |
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what are the components of the delivery dose? (what kind of beams) |
primary beam scatter
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dmax depth: 60 cobalt |
0.5 cm |
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dmax depth: 4MV |
1.0 cm |
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dmax depth 6MV |
1.5 cm |
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dmax depth 10MV |
2.5 cm |
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dmax depth 18MV |
3.5 cm |
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purpose of beam altering devices |
changes the isodose distribution |
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reasoning for beam alteration |
for critical structures for sloping surfaces |
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bolus what is the literal meaning |
"mass" of something |
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what does a bolus do |
it increases the dose to the skin surface by filling in area lacking in tissue (even contour) |
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three purposes of the bolus |
enhance skin dose (creates false skin to eliminate skin sparing)
even out irregular countours of the skin surface to maintain standard isodose curve shape
absorption of scatter |
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what part of the wedge attenuates the beam the most |
heel of the wedge |
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benefit of wedge over bolus |
maintains skin sparing |
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purpose of wedge |
to prevent hot spots from when there is an overlap with the beam due to hinge angles less than 180 |
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hinge angle |
the angle between the central axis of two beams |
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wedge angle |
the angle at which an isodose curve is tilted at the central ray of the beam at a given depth |
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what is a wedge usually made of |
lead, steel, brass |
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standard wedge sizes |
15, 30, 45, 60 |
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individual wedges |
made specifically for each patient |
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internal wedge |
60 degree wedge placed into the machine allows custom wedge angle ( 0 to 60) no field size restraint |
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disadvantages of wedges |
not individualized field size restrictions for manual wedges maintain standard distance from patient |
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compensator |
compensates for irregular patient contours |
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advantages of compensator |
maintains skin sparing it is individualized |
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compensator -construction |
does not have to be a tissue equivalent, preferably medium density
made of lead, copper, brass, polyethylene, lucite |
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compensator advantage over bolus |
skin sparing effect maintained |
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factors to consider when designing compensator |
beam divergence linear attenuation coefficience (does not need to be tissue equivalent) |
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other methods of changing isodose curve |
temporary blocks transmission blocks |
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devices that change the beams character |
beam blocking degrader and spoilers |
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beam spoiler and degrader what does it do |
it is placed in the path of the beam and changes the beams character |
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purpose of beam spoiler and degrader |
it enhances surface dose |
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when do we use beam spoilers and degraders... |
treating total skin irradiation and skin involvement |
