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Laura Nappi online course > Beam Energy > Flashcards

Beam Energy Flashcards

1
Q

T/F: you CAN find beam energy on the treatment prescription/plan

A

TRUE

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2
Q

beam energy choice depends on what factors? (3)

A
  1. thickness of patient
  2. depth of tumor
  3. if skin sparing is desired
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3
Q

generally for patient separation/thickness LESS than 22 cm, what beam energy is used?

A

4-6 MV

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4
Q

generally for patient separation/thickness MORE than 22 cm, what beam energy is used?

A

10-18 MV

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5
Q

as beam energy increases, what happens to DMAX?

A

DMAX also increases

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6
Q

what is dmax for a 4MV beam?

A

1 cm

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7
Q

what is dmax for a 6MV beam?

A

1.5 cm

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8
Q

what is dmax for a 10MV beam?

A

2.5 cm

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9
Q

what is dmax for a 15MV beam?

A

3.0 cm

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10
Q

what is dmax for a 20MV beam?

A

3.5 cm

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11
Q

what is dmax for a 25MV beam?

A

5 cm

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12
Q

what is dmax for a 6MeV beam?

A

1.5 cm

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13
Q

what is dmax for a 9MeV beam?

A

2.2 cm

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14
Q

what is dmax for a 12MeV beam?

A

2.8 cm

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15
Q

______ = point at which 100% of dose is distributed within patient

A

dmax

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16
Q

as beam energy increases, so does dmax - what happens to the skin sparing?

A

increases as well

–dmax increases, so does beam energy, and skin sparing –> cause penetrates further into body and not as close to skin surface

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17
Q

what is the green region on this photon PDD and depth graph?

A

build up region

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18
Q

what is NOT spared when using electron?

A

the skin is NOT spared

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19
Q

what is the green region on this drawn diagram of a patient getting a photon trt?

A

build up region

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20
Q

which curve is representing electrons and which curve is representing photons?
PINK VS BLUE

A

pink = photons MV
blue = electrons MeV

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21
Q

once an ___MeV/MV___ beam hits skin surface, it will begin to build up until it hits dmax releasing 100% dose there

A

MV (photon)

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22
Q

what type of beams are very superficial?

electrons or photons

A

electrons

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23
Q

nearly ___% of electron beam is delivered at skin surface

A

100%

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24
Q

for photon beams, ___-___% of dose is delivered to skin surface and then 100% at dmax

**this can change/depends on beam energy selected

A

25-35%

25
Q

which beam energy participates in skin sparing effect?

A

PHOTON (MV)

26
Q

once an electron hits dmax, what happens?

A

they abruptly fall to zero; zero %
–this is how other tissues are spared during e- treatments, unlike photons

27
Q

unlike photons, electrons start off high meaning they do not need a _______ region

A

build up region
–there is no build up region for electrons

28
Q

which curve correlates to electrons, and which for photons?

A

PINK = photons (MV)
BLUE = electrons (MeV)

29
Q

which isodose curve belongs to electrons… and which for photons?

A

A. deeper curves- PHOTON
B. shallow curves - ELECTRONS

30
Q

higher beam energies yield ___greater/lesser___ PDDs

A

GREATER

31
Q

higher energies have ___smaller/larger___ gaps between skin surface and dmax

A

larger

32
Q

which isodose curve is a higher energy photon beam, and which belongs to a lower energy photon beam?

A

A. lower energy isodose curve
B. higher energy isodose curve

**we know by looking at dmax and gaps between skin surface and dmax

33
Q

concept check:
For whole brain treatments we use lower energy beams, what would happen is we used higher energies?

A

we’d miss tissue right next to skull, as beam would penetrate straight on through

34
Q

T/F: there IS a shape difference between electron and photon isodose curves

A

true

35
Q

which isodose curve is a rough sketch of a photon curve and which is an electron?

A

A. electrons
B. photons

36
Q

on electron isodose curves … higher energy lines ______ laterally

A

constrict laterally

37
Q

low energy electron isodose curve lines are ___closer/farther___ - whereas high energy e- isodose curve lines are __closer/farther__

A

low energy lines —> closer
high energy lines –> farther

**safe to assume same for high/low energy photons beams

38
Q

what is Bowing Effect on electron isodose curves?

A

when low energy isodose lines expand laterally
–Bowing Effect is due to beam scatter! –> e- scatter easy

39
Q

what causes Bowing Effect for electron isodose curves?

A

beam scatter

40
Q

Photon or Electron isodose curves –
penetrate in a more forward direction

A

PHOTONS

41
Q

Photon or Electron isodose curves –
are very superficial

A

ELECTRONS

42
Q

Photon or Electron isodose curves –
have greater energies available at greater depths

A

PHOTONS

43
Q

CA = _____ ______

A

Central Axis

44
Q

what is equation to find 80% central axis depth dose of electrons?

A

E/3

45
Q

what is equation to find 90% central axis depth dose of electrons?

A

E/4

46
Q

what/where is Therapeutic Range of electrons?

A

90%

47
Q

___-___% isodose lines of electrons are most useful because after them, the dose falls off/electrons lose energy at a high rate

A

80-90%

48
Q

electrons lose ___ MeV per cm in water or soft tissue

A

2 MeV/cm

49
Q

once dmax is hit for electrons where does any dose after that come from?

A

mainly from contamination, not the primary beam

50
Q

what does “dose fall off” mean?

A

losing energy at a high rate

51
Q

________ are heavier, charged particles that scatter at smaller angles

A

protons

52
Q

protons compared to electrons, which have a larger scatter angle?

A

electrons

53
Q

protons, compared to electrons and photons, are slowed by __lower/higher___ Z materials

A

lower

54
Q

what is another name for proton dmax?

A

bragg peak

55
Q

a proton bragg peak is typically too narrow to cover a whole tumor/ enough tumor volume - SO what happens

A

SOBP ; several beams of different energies are used to spread out the Bragg Peak

56
Q

what does SOBP stand for?

A

Spread Out Bragg Peak

57
Q

protons:
a _______ ensures that the most superficial/proximal, to the most distal/deepest part of tumor is covered

A

SOBP - Spread out bragg peak

58
Q

an SOBP creates what

A

a flatter, longer line we can use to treat larger areas w/ protons

59
Q

the following is an example of what?
A =
B =

A

A –> Bragg Peak
B –> SOBP - spread out bragg peak

Laura Nappi online course (54 decks)

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