TAR, TMR, extended factors, wedges (treatment dose and prescription)

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18 Terms

1
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what’s the ratio of an absorbed dose at a depth within the phantom at a given distance compared with the absorbed dose in free space at the same distance

tissue air ratio

2
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relationship btw

energy

TAR

up

up

3
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relationship btw

field size

TAR

up

up

4
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relationship btw

TAR

depth ? past d max due to beam attenuation

down

increase

5
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what’s the ratio of an absorbed dose at a specified depth in a phantom to the absorbed dose at d max at same distance from the radiation source

tissue maximum ratio TMR

6
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extended distances have SSD that are greater than what?

isocenter

7
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what changes the shape of the isodose curve and dose distribution within patient

wedges

8
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(T/F) field sizes cannot be larger, than the wedge itself

T

9
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(T/F) wedges “harden” the beam, meaning the low energy photons are absorbed by the wedge, so a lower number of photons are available for dose

T

10
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ratio of the dose rate at a point off axis to the dose rate at a point on the central axis at the same distance from the source

off axis ratio

11
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what are some factors that can change the isodose

beam energy

beam type

SSD

field weighting

beam modifiers

field size

12
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why are higher energy beams isodose curves are more spread out than lower energy beams

because the higher energy beams are more penetrating

13
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what shows the dose that normal tissue and tumor will receive during the treatment

dose volume histograms

14
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if a tray is used what must be increased

MU

15
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if bolus brings the dose closer to the skin surface and decreases what

skin sparing

16
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(T/F) bolus will attenuate some of the beam but does not require a factor to be addd into the calculation for MU

T

17
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what factor shows how much of the beam is transmitted through the wedge or compensator

transmission factor

18
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what factor compares the dose rate in a known field size to the dose rate in a reference field size

output factor