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Radiation Therapy > Principles and Practice Review 1 > Flashcards

Principles and Practice Review 1 Flashcards

1
Q

Which of the following is not found inside the head of a linear accelerator ?

A

accelerator structure

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2
Q

The backscatter factor is effected by all of the following EXCEPT:

  1. Treatment field size
  2. Radiation quality
  3. Quantity of radiation
A

Quantity of Radiation

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3
Q

The tissue air ratio (TAR) at the depth of maximum electron buildup (Dmax) is:

  1. Always less than or equal to 1
  2. The backscatter factor
  3. Dependent on the field size
A

All of the above

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4
Q

The concept of tissue-air ratio (TAR) is most commonly employed for calculations involving:

A

SSD varying fields

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5
Q

The depth of maximum ionization is most dependent on

A

Beam energy

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6
Q

A 10MV linear accelerator is used at 100cm SSD. The location of maximum dose is found at a depth of

A

2.5cm

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7
Q

Percentage depth dose increases with increasing:

  1. Energy
  2. Depth
  3. Field Size
A

Energy and Field size

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8
Q

Tissue-air ratio decreases with decreasing

  1. SSD
  2. Depth
  3. Field size
A

Field size

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9
Q

A wedge filter _____ the output of the beam and must thus be taken into account in the treatment calculations

A

decreases

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10
Q

%DD increases with increasing

  1. energy
  2. depth
  3. field size
A

energy and field size

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11
Q

TAR decreases with decreasing

  1. field size
  2. depth
  3. SSD
A

Field size

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12
Q

When blocking is used in a treatment calculation, the area of the collimator is used in determining

  1. TMR
  2. Output Factor
  3. PDD
A

Output Factor

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13
Q

Which of the following is not a tissue absorption factor?

A

Output factor

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14
Q

Which of the following central axis depth dose quantities would most likely be used to compute an accurate MU setting on an 18MV unit for an isocentric treatment

A

TMR

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15
Q

Two parallel opposed equally weighed 6MV fields are separated by 20cm of tissue and treated with an SSD technique. The maximum dose will occur

A

1.5 under the skin surface

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16
Q

A wedge filter ______ the output of the treatment beam and must thus be taken into account in the treatment calculation

A

decreases

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17
Q

Mayneord’s factor is used to convert

A

PDD with a change in SSD from the standard

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18
Q

1Gy is the same as

A

100cGy

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19
Q

The point of maximum electron equilibrium is referred to as

A

Dmax

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20
Q

Dose rates:

A

Increase with increased field size and decrease with increased distance

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21
Q

In a fixed SSD technique the dose is routinely normalized

A

at Dmax

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22
Q

In an isocentric treatment technique the most done is routinely normalized

A

at the isocenter

23
Q

What is the reference desert when delivering an external beam radiation therapy treatment using a 10MV SSD technique?

A

.968

24
Q

What is the reference desert when delivering an external beam radiation therapy treatment using a 18MV SSD technique?

A

2.1

25
Q

Calculate the equivalent square of a 13x12cm field blocked 12%

A

11.7

26
Q

Calculate the equivalent square of a 13x9cm field blocked 7%

A

10.3

27
Q

The gross tumor volume (GTV) ], as defined by the ICRU, mean:

A

The gross tumor volume (GTV) as defined by the ICRU name

28
Q

The term clinical target volume (CTV), as defined by the ICRU, means

A

A tissue volume that contains demonstrable GTV a defend volume

29
Q

The field size when using an SSD technique and a photon mean usually defined

A

on the skin surface

30
Q

The angle of beam divergence is

A

larger farther from the CAX

31
Q

The three planes in a patient are across the body, along the body in a lateral view, and along the body in an anterior view. Respectively they are referred to as

A

axial, sagittal, and coronal

32
Q

When the treatment field is designed by the radiation oncologist, margins are always added around a tumor because of

A

uncertainties in determining tumor extent, penumbra of the be a, and patient motion

33
Q

the isocenter is

A

the point around which the source of the beam rotates

34
Q

What is the percent depth dose of a 12x7cm field delivering a 10 MV x-ray at a depth of 2.5cm?

A

100.0

35
Q

What is the percent depth dose of a 12x7cm field delivering a 18MV x-ray at a depth of 2.5cm?

A

97.3

36
Q

What is TAR of a 10x16cm field blocked 5% delivering a 10 MV x-ray at a depth of 10.0cm

A

.866

37
Q

The depth of maximum ionization is most dependent upon

A

beam quality

38
Q

TAR is dependent upon:

  1. Energy
  2. SSD
  3. Depth
  4. Field Size
A

Energy
Depth
Field Size

39
Q

When using shielding blocks what is effected?

A

Equivalent square field (ESF)

40
Q

The intensity of a high energy photon beam at any given distance from a source is:

A

inversely proportional to the square of the distance

41
Q

Dose rate for a linear accelerator is expressed at

A

cGy?MU

42
Q

TAR is advantageous because

A

ratios do not depend on source to skin distance

43
Q

Mayneord factor compensates for a change in central axis depth dose and includes corrections for

A

inverse square law

44
Q

Which beam would produce the maximum amount of backscatter

A

the one with least energy usually 1.25MV

45
Q

As beam quality increases, maximum dose____.

A

increases

46
Q

The %DD for a 12x12cm field, 4MV photon beam, 5cm depth, and 80cm SSD is 82.8. Calculate the %DD for the same field size and depth for 100cm SSD.

A

84.3

47
Q

If the field size indicator is set for 20x20cm at 80cm SSD, what is the field size at 84cm?

A

21x21cm

48
Q

If a Co-60 unit is used at 80cm SSD for a 15x15cm field size and has a %DD of 58.4 at 10cm depth, what is the %DD for the same field size and depth at 100cm SSD?

A

60.9

49
Q

The Dmax for a 10MV photon beam at an 100cm SSD with a 15x15cm field is approximately

A

2.5cm

50
Q

Mayneord’s F-factor is of use when there is a change in

A

SSD

51
Q

Calculate the equivalent square for a 10x15cm rectangular field

A

12x12cm

52
Q

Determine the equivalent square for a rectangular field with a width of 8cm and a length of 15cm

A

10.4cm

53
Q

Determine the equivalent square for a rectangular field with a width of 7cm and a length of 17cm

A

9.9cm

54
Q

The counterpart of the timer setting of a Co-60 unit is most similar to the ______of a LINAC.

A

monitor unit

Radiation Therapy (3 decks)

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