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23 Cards in this Set
- Front
- Back
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total tumor dose depends on:
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-aim of tx. (cure, control, palliation)
-radiosensitivity of tumor and critical structures -study and experience in the field |
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fractionatin
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dividing does into smaller units rather than giving as one large dose
-minimizes normal tissue damage |
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Advantages of higher energy beams
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-greater penetration
-greater skin paring -predominantly forward scatter -more unifrom energy absorption |
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geometric parameters
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field size and shape
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field size affects
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TAR
% DD BSF they have direct relationship |
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tumor depth affects
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% DD, TAR, and BSF with inverse relationship
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distance affects
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% DD, intensitfy and field size (as distance increase % DD increase as does field size and intensity decrease by the invers square law)
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percent depth dose definition
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ratio of dose at depth to the dose at dmax depth, multiplied by 100%. Used for SSD calculations
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PDD depends on
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SSD
Energy Field size depth of tumor |
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As SSD increase, PDD__
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increase
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as energy increase PDD ___
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increases
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as field size increases, PDD ___
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increases
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as depth of tumor increases, PDD___
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decreases
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Tissue air ratio
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Ratio of dose at some depth in a phantom to the dose at the same point in air. Used for SAD calcuations
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Tissue phantom ratio
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Ratio of the dose at some depth in phantom to the dose at a reference depth in a phantom
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Tissue Maximum Ratio
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Special case of TPR when the reference depth is equal to the dmax depth
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TAR, TMR, TPR depend on
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energy
field size depth INDEPENDENT OF SSD |
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as energy increses what happens to TAR, TMR, TPR
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increases
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as field size increase what happens to TAR, TMR, TPR
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increases
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as depth increases what happens to TAR, TMR, TPR
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decreases
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Backscatter Factor (BSF)
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Is a special case of TAR at dmax
BSF= TAR at dmax/ TAR in air |
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Output factor
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the output of the linac is comprised of 2 factors, Collimator Scatter (Sc) and Phantom Scatter (Sp). The product of the two is total scatter, commonly called output
Output= Sc x Sp |
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Mayneord's F factor
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used to modify FDD (PDD, % DD) for non-standard SSDs
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