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Dosimetry > Electrons > Flashcards

Electrons Flashcards

1
Q

choose e- to give ? DD

A

90% DD to desired depth, which is 1/2 of the probable e- E

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2
Q

e- used to treat lesions at what depth

A

superficial lesions < 7cm in depth

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3
Q

e- advantages over superficial regarding bone dose

A

no increase dose to bone

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4
Q

e- beam calc algorithm

A

pencil beams

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5
Q

e- are scattered outward by

A

steep projection

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6
Q

e- are scatter inward by

A

steep depression

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7
Q

e- max range dependent on

A

E

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8
Q

e- fall off is

A

rapid dose fall off

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9
Q

e- skin dose is

A

high

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10
Q

tx head component for e-

A
  • scattering foil

- no target

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11
Q

e- significant impact on tissue ?

A

inhomogeneities

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12
Q

brems tail is what on a beam curve

A

slowly decreasing portion of an e- beam curve

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13
Q

Rp stands for

A

practical range

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14
Q

e- block thickness formula

A

MeV/2 + 1

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15
Q

R90 is

A

MeV/4

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16
Q

R80 is

A

MeV/3

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17
Q

ballooning effect on e- requires you need to adequately

A

cover target volume

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18
Q

in field blocking, block thickness must be adequate to reduce transmission to

A

< 5%

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19
Q

e- cone size affects

A

beam output

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20
Q

e- cone distance from pt

A

at least 5cm from skin surface

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21
Q

uniformity of e- beams are better than

A

photon beams

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22
Q

if air gap increases dose ?

A

dose decreases

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23
Q

TBI uses

A

spoilers

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24
Q

spoiler scatters

A

e-

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25
Q

TBI total dose

A

12 Gy

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26
Q

TBI dose rate

A

10-15 cGy/min

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27
Q

TBI frequency

A

bid

28
Q

dose rate of e- varies with

A

field size & E

29
Q

%DD e- depends on

A

E

30
Q

to calc e- E you take ? of tumor

A

3x max depth of tumor

31
Q

field margin for e- must be selected so target lies within?

A

90% line

32
Q

e- range in lung is increased by a factor of

A

3

33
Q

CET stands for

A

coefficient of equivalent thickness

34
Q

in CET, the attenuation by a given thickness of inhomogeneity is equivalent to

A

attenuation by a certain thickness of water

35
Q

CET for compact bone

A

1.5 g/cm^3

36
Q

CET for spongy bone

A

1.1 g/cm^3

37
Q

e- density of lung tissue varies depending on

A

depth

38
Q

dose in tissue from of a less dense area (air/lung) is ?

A

decreased b/c scattering less

39
Q

e- range is larger in lung (less dense tissue) making lung dose ?

A

increase

40
Q

therapeutic range of e-

A

90% iso line (E/4)

41
Q

when CW tx w/e-, beam E is often chosen so what line is at interface?

A

80% line

42
Q

e- matching at surface causes ? at depth

A

hot spot

43
Q

e- advantages over superficial regarding skin sparing

A

small amount of skin sparing

44
Q

e- advantages over superficial regarding underlying tissue

A

greater sparing of underlying tissue

45
Q

e- advantages over superficial regarding output

A

greater output & faster treatment

46
Q

brems tail is generated where

A

scattering foil

47
Q

brems tail represents

A

photon contamination

48
Q

Rp is where e- have actually

A

stopped

49
Q

Rp formula

A

MeV/2

50
Q

e- block thickness below 10 MeV is

A

3mm block

51
Q

ballooning effect occurs with what radiation

A

e-

52
Q

what do higher isolines look like on ballooning effect

A

taper

53
Q

ballooning effect requires larger than expected

A

field size to cover entire volume

54
Q

ballooning effect aka

A

flowering pot effect

55
Q

isolines appear ? in ballooning effect

A

flat

56
Q

e- blocking affects

A

beam output

57
Q

e- SSD affects

A

beam output

58
Q

uniformity of e- beams have smaller ? than photon beams

A

horns at beam edge

59
Q

if air gap increases dose profile is

A

more rounded

60
Q

in TBI, surface dose increases with ? spoiler to surface distance

A

decreased

61
Q

in TBI, point of max dose build up moves closer to surface with ? spoiler to surface distance

A

decreased

62
Q

in TBI, ? becomes principle source of e- contamination of beam

A

spoiler

63
Q

what increases dose to tissue in buildup region for TBI

A

spoiler

64
Q

only 20-50% isoline into penumbra region causes difficulty in what

A

matching fields

65
Q

CET can be used to correct

A

e- change in dose

66
Q

e- density of lung tissue average is

A

0.5 g/cm^3

67
Q

Lateral scatter equilibrium exists when the field size is ? Of the e- energy

A

Of the order of the e- energy

Dosimetry (53 decks)

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