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Dosimetry > Electrons > Flashcards

Flashcards in Electrons Deck (67):
1

choose e- to give ? DD

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

2

e- used to treat lesions at what depth

superficial lesions < 7cm in depth

3

e- advantages over superficial regarding bone dose

no increase dose to bone

4

e- beam calc algorithm

pencil beams

5

e- are scattered outward by

steep projection

6

e- are scatter inward by

steep depression

7

e- max range dependent on

E

8

e- fall off is

rapid dose fall off

9

e- skin dose is

high

10

tx head component for e-

-scattering foil
-no target

11

e- significant impact on tissue ?

inhomogeneities

12

brems tail is what on a beam curve

slowly decreasing portion of an e- beam curve

13

Rp stands for

practical range

14

e- block thickness formula

MeV/2 + 1

15

R90 is

MeV/4

16

R80 is

MeV/3

17

ballooning effect on e- requires you need to adequately

cover target volume

18

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

< 5%

19

e- cone size affects

beam output

20

e- cone distance from pt

at least 5cm from skin surface

21

uniformity of e- beams are better than

photon beams

22

if air gap increases dose ?

dose decreases

23

TBI uses

spoilers

24

spoiler scatters

e-

25

TBI total dose

12 Gy

26

TBI dose rate

10-15 cGy/min

27

TBI frequency

bid

28

dose rate of e- varies with

field size & E

29

%DD e- depends on

E

30

to calc e- E you take ? of tumor

3x max depth of tumor

31

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

90% line

32

e- range in lung is increased by a factor of

3

33

CET stands for

coefficient of equivalent thickness

34

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

attenuation by a certain thickness of water

35

CET for compact bone

1.5 g/cm^3

36

CET for spongy bone

1.1 g/cm^3

37

e- density of lung tissue varies depending on

depth

38

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

decreased b/c scattering less

39

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

increase

40

therapeutic range of e-

90% iso line (E/4)

41

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

80% line

42

e- matching at surface causes ? at depth

hot spot

43

e- advantages over superficial regarding skin sparing

small amount of skin sparing

44

e- advantages over superficial regarding underlying tissue

greater sparing of underlying tissue

45

e- advantages over superficial regarding output

greater output & faster treatment

46

brems tail is generated where

scattering foil

47

brems tail represents

photon contamination

48

Rp is where e- have actually

stopped

49

Rp formula

MeV/2

50

e- block thickness below 10 MeV is

3mm block

51

ballooning effect occurs with what radiation

e-

52

what do higher isolines look like on ballooning effect

taper

53

ballooning effect requires larger than expected

field size to cover entire volume

54

ballooning effect aka

flowering pot effect

55

isolines appear ? in ballooning effect

flat

56

e- blocking affects

beam output

57

e- SSD affects

beam output

58

uniformity of e- beams have smaller ? than photon beams

horns at beam edge

59

if air gap increases dose profile is

more rounded

60

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

decreased

61

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

decreased

62

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

spoiler

63

what increases dose to tissue in buildup region for TBI

spoiler

64

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

matching fields

65

CET can be used to correct

e- change in dose

66

e- density of lung tissue average is

0.5 g/cm^3

67

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

Of the order of the e- energy