Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Residency > First Year Exam: Rules of Thumb and Values to Memorize > Flashcards

First Year Exam: Rules of Thumb and Values to Memorize Flashcards

1
Q

What is the approximate pdd(10) for a 6MV beam?

A

65-67%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the approximate pdd(10) for a 6FFF beam?

A

63-64%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the approximate pdd(10) for a 10MV beam?

A

73-75%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the approximate pdd(10) for a 10FFF beam?

A

70-71%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the approximate pdd(10) for a 15MV beam?

A

76-77%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the approximate pdd(10) for a 18MV beam?

A

80%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the approximate dmax for a 6FFF beam?

A

1.4 - 1.5 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the approximate dmax for a 6MV beam?

A

1.4 - 1.5 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the approximate dmax for a 10FFF beam?

A

2.2 - 2.4 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the approximate dmax for a 10MV beam?

A

2.2 - 2.4 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the approximate dmax for a 15MV beam?

A

2.7 - 2.9 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the approximate dmax for a 18MV beam?

A

3.3 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the approximate dmax for a Co-60 beam?

A

0.5 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the approximate pdd(10) for a Co-60 beam?

A

55%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the attenuation rate dose fall-off rule of thumb for 6MV beams past dmax?

A

3%/cm

NOTE: This is just attenuation. The actual fall-off rate differs because it’s also inverse square dependent, and the inverse square fall-off varies with distance from source. So this 3%/cm you can only use for TMR, but it’s not as applicable for PDD. For PDD, expect something larger than 3%/cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the attenuation rate dose fall-off rule of thumb for 10MV beams past dmax?

A

2.5%/cm

NOTE: This is just attenuation. The actual fall-off rate differs because it’s also inverse square dependent, and the inverse square fall-off varies with distance from source. So this 2.5%/cm you can only use for TMR, but it’s not as applicable for PDD. For PDD, expect something larger than 2.5%/cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the attenuation rate dose fall-off rule of thumb for 18MV beams past dmax?

A

2%/cm

NOTE: This is just attenuation. The actual fall-off rate differs because it’s also inverse square dependent, and the inverse square fall-off varies with distance from source. So this 2%/cm you can only use for TMR, but it’s not as applicable for PDD. For PDD, expect something larger than 2%/cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the average energy of a photon beam?

A

Max energy / 3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is a change in flatness indicative of a change in energy?

A

A 10% change in flatness corresponds to a 1% change in energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the average energy of an electron beam at patient surface?

A

Equal to Emax (since electron beams are close to monoenergetic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

If given E0, what is the approximate R50 in water?

A

R50(cm) = E0/2.33

NOTE: This is actually an overestimation. The actual measurement of R50 is typically a bit below what this equation predicts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

If given E0, what is the approximate R80 in water?

A

R80(cm) = E0/2.9

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

If given E0, what is the approximate R90 in water?

A

R90(cm) = E0/3.2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

If given E0, what is the approximate Rp in water?

A

Rp(cm) = E0/2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is approximate bremmstrahlung tail for 6E, 12E and 20E respectively?

A

6E - 1%
12E - 2%
20E - 5%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is approximate dmax of a 6E beam?

A

1.2 - 1.3 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is approximate dmax of a 9E beam?

A

1.9 - 2.1 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is approximate dmax of a 12E beam?

A

2.8 - 2.9 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is approximate dmax of a 16E beam?

A

3.0 - 3.1 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is approximate dmax of a 20E beam?

A

2.5 cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the approximate surface dose for electrons with energies between 6E and 20E, and how does it change with increasing energy?

A

78 - 95%

Increases with increasing energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the approximate surface dose for photons with energies between Co-60 and 20MV, and how does it change with increasing energy?

A

20 - 50%

Decreases with increasing energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is the equivalent square field equation?

A

A/P = A/P or…

x^2/4x = AB/2(A+B)

Solve for x

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is approximate scatter at 1 meter from a phantom?

A

1/1000th the primary beam

35
Q

What is the maximum energy of lateral photon scatter?

36
Q

What is the maximum energy of backscattering photons?

37
Q

How are the Compton, PE, and PP mass attenuation coefficients proportional to Z?

A

Compton mass atten - independent of Z, proportional to electron-density

PE mass atten - proportional to Z^3

PP mass atten - proportional to Z

38
Q

What isodose line is LINAC based SRS usually prescribed to? What about Gamma Knife?

A

LINAC: 80% line

GK: 50% line

39
Q

What is approximate scatter outside of field as a percentage of central axis dose for physical and dynamic wedges?

A

Physical: ~2.5% of central axis dose

Dynamic: ~1% of central axis dose

40
Q

What is the approximate R50 of a 6E beam?

A

2.3 - 2.4 cm

41
Q

What is the approximate R50 of a 9E beam?

A

3.5 - 3.6 cm

42
Q

What is the approximate R50 of a 12E beam?

43
Q

What is the approximate R50 of a 16E beam?

44
Q

What is the approximate R50 of a 20E beam?

A

8.3 - 8.5 cm

45
Q

What is the general rule of thumb for lead shielding needed for electron machine of max energy E?

A

Thickness of lead (mm) = E(MeV) / 2

Or sometimes I’ve seen

Thickness of lead (mm) = Thickness of water / 11

46
Q

Rate of electron beam attenuation in lead

47
Q

What thickness of cerrobend is needed to stop an electron beam?

A

Thickness in mm = 1.2*thickness in lead

48
Q

To estimate margin for PTV, what is the equation used?

A

margin = 2.5ε + 0.7σ

Where ε is systematic uncertainty (setup, motion, imaging, etc) (possible to reduce with IGRT)

σ is random uncertainty (very hard to reduce)

49
Q

What is the approximate therapeutic range of an electron beam given E?

A

Therapeutic range ~ E/3 cm

50
Q

Given energy of an electron beam, what equation approximates surface dose?

A

E + 73%
Or
E + 72%

51
Q

What is the speed of sound in soft tissue?

52
Q

Approximately how much dose do you receive from a CT scan?

A

50 - 75 mGy

53
Q

What is the approximate HU of air?

54
Q

What is the approximate HU of lung?

55
Q

What is the approximate HU of soft tissue?

A

-300 to -100

56
Q

What is the approximate HU of fat?

57
Q

What is the approximate HU of water?

58
Q

What is the approximate HU of CSF?

59
Q

What is the approximate HU of blood and muscle?

60
Q

What is the approximate HU of spongy bone?

61
Q

What is the approximate HU of cortical bone?

A

up to 3000

62
Q

In a T1 weighted MRI, what appears bright and what appears dark?

A

Fat is bright, CSF and water are dark

63
Q

In a T2 weighted MRI, what appears bright and what appears dark?

A

Bone is dark, water and CSF are bright

64
Q

In a FLAIR image, what appears bright and what appears dark?

A

FLAIR is same as T1, except all fluid signal is removed

So fat is bright, CSF and water are dark

65
Q

What is a typical MLC intra-leaf leakage?

66
Q

What is a typical MLC inter-leaf leakage?

67
Q

What is a typical MLF leaf-end leakage?

A

15% to 24%

68
Q

What is the approximate Z of air?

69
Q

What is the approximate Z of tissue?

70
Q

What is the approximate Z of bone?

71
Q

What is the approximate Z of prostheses?

72
Q

What is the approximate density of lead?

A

11.34 g/cc

73
Q

What is the approximate density of air?

A

0.0012 g/cc

74
Q

What is the approximate density of lung?

75
Q

What is the approximate density of bone?

76
Q

What is the approximate density of tungsten?

A

19.25 g/cc

77
Q

What is the approximate density of tissue?

78
Q

What is the equation for average energy at depth (z) for an electron beam?

A

Eo*(1-z/Rp)

79
Q

What is the rule of thumb for dose calculation error due to HU value error?

A

10% error in HU value yields a 2% error in calculated dose

80
Q

What is the average magnitude of tumor motion in lung? What is the absolute maximum?

A

1 cm average

5 cm max

81
Q

What is average out of field energy compared to in-field energy?

A

4-10% in field energy

82
Q

What are typical doses for…

kV planar:

MV planar:

kV CBCT:

MV CBCT:

A

What are typical doses for…

kV planar: 0.5 - 1mGy

MV planar: 1-3cGy

kV CBCT: 1cGy

MV CBCT:15-20cGy

83
Q

What are the following dmax’s? (used in MD Anderson TLD check)

6X
6XFFF
10X
10XFFF
15X
A 
6X - 1.4 cm
6XFFF - 1.4 cm
10X - 2.2 cm
10XFFF - 2.2 cm
15X - 2.7 cm
84
Q

What are the following dmax’s? (used in MD Anderson TLD check)

6E
9E
12E
16E
20E
A 
6E - 1.3 cm
9E - 2.1 cm
12E - 2.9 cm
16E - 3.0 cm
20E - 2.0 cm

Residency (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions