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FOR BOARDS > fun with physics > Flashcards

fun with physics Flashcards

1
Q

the depth within the body that receives the same dose of radiation

A

isodose line

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2
Q

compensates for curves in the body

A

compensators

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3
Q

adjusts the beam profile to reduce the dose to more sensitive parts of the body

A

wedges

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4
Q

measurement made by passing a dosimeter across the beam

A

dose profile

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5
Q

measure of the side to side quality of the beam; usually required to be +/- 1-2% from one side of the beam to the other

A

symmetry

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6
Q

generally the max variation of the beam intensity in the central 80% of the beam; required to be +/- 2-3% across the beam

A

flatness

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7
Q

the TAR at max on the CAX of the beam is referred to as what?

A

Backscatter factor

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8
Q

the region between the patient’s skin and the max is referred to as what?

A

dose build up region

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9
Q

the absorbed dose at a given depth expressed as a % of the absorbed dose at a reference depth on the CAX of the field

A

PDD

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10
Q

PDD is dependent on what 5 variables?

A

energy, field size, SSD, depth, composition of the irradiated medium

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11
Q

does PDD increase or decrease with increased SSD

A

increase

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12
Q

does PDD increase or decrease with increasing field size

A

increase

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13
Q

does PDD increase or decrease with increased depth

A

decrease

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14
Q

what is dose in tissue/ dose at d-max in a phantom

A

TMR

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15
Q

what 3 factors is TMR dependant

A

depth, energy, field size

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16
Q

what is used to calculate changes in PDD

A

Mayneord’s Factor

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17
Q

what is dose in tissue/dose in air?

A

TAR

18
Q

ratio of dose on the CAX at d-max to dose at the same point in air

A

BSF

19
Q

BSF and __ at dmax are the same

A

TAR

20
Q

is TMR dependent on SSD

A

no

21
Q

Which of the following is true when measuring Percent Depth Dose (PDD)?
A. The Source to Chamber distance is constant.
B. The chamber to Axis distance is constant.
C. The Source to Surface distance is constant.
D. The chamber depth is constant.

A

C. the source to surface distance is constant

22
Q

Which of the following is most often used to measure beam quality of a megavoltage photon beam?
A. PDD at 10 cm
B. TPR ratio at 20cm and 10 cm C. Half Value Layer
D. Depth where PDD is 50%
E. a and b only.

A

E. A and B only

23
Q

at approximately what energy does backscatter factor become no longer meaningful?

A

10 MV

24
Q 
The reference depth for the Tissue Phantom Ratio, TPR, is:
A. dmax. 
B. 5 cm. 
C. 10 cm. 
D. dependent on measurement choice
A

D. dependent on measurement choice

25
Q

what is D-max

A

depth of the max dose

26
Q

where are PDD 10 and TPR 20/10 measured

A

central axis

27
Q

with TPR does the SSD change

A

yes

28
Q

does scatter increase or decrease with field size

A

increase

29
Q

with TAR, is the SCD constant? what about the measurement point?

A

with TAR the SCD and measurement point are constant

30
Q

TAR varies with what 3 things

A

depth, field size, energy

31
Q

dose at a point divided by the dose at d-max

A

depth dose

32
Q

does depth dose increase or decrease with increasing field size

A

increase

33
Q

will a shorter SSD make the depth dose go up or down

A

down

34
Q

two measurements are made, one in phantom and one in air at the same time

A

TAR

35
Q

a variation of TPR but the reference depth is usually taken to be D-max

A

TMR

36
Q

a ratio of dose in a phantom divided by the dose in a phantom at a reference depth

A

TPR

37
Q

what parameter is used to calculate the scatter dose component of a blocked field

A

scatter maximum ratio

38
Q

Which of the following is true when measuring TPR?
A. The Source to Chamber distance is constant.
B. The chamber to surface distance is constant.
C. The Source to Surface distance is constant.
D. The chamber depth is constant.

A

A. the source to chamber distance is constant

39
Q

what is penumbra?

A

area or region at the beams edge where the radiation. intensity falls to 0

40
Q

when treating a patient with skin cancer and using electrons, which does the electron use, a scattering foil or a flattening filter?

A

scattering foil

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