Electron Characteristics

Question 1

Are collisional loses (electrons) more predominant in Low or High Z materials?

Answer 1

Low Z materials

Question 2

What are collisional loses dependent on?

Answer 2

Electron Density of Medium

Question 3

Is MSP greater in low or high Z materials?

Answer 3

Low Z materials

Question 4

Radiation loses of electron interaction (bremsstrahlung) is proportional to ______

Answer 4

Proportional to E - as E increases, bremsstrahlung increases;
Proportional to Z^2 - as Z increases, bremsstrahlung increases

Question 5

Define MCS

Answer 5

Multiple Coulomb Scattering; form of electron scattering

Question 6

Low energy e’ and higher Z result in:

Answer 6

more scattering

Question 7

What type of Z material is used for LINAC scattering foils?

Answer 7

High

Question 8

What is a delta ray?

Answer 8

Scattered electrons that can cause ionization

Question 9

What do Inelastic interactions with electrons cause?

Answer 9

Ionization and Excitation

Question 10

What is the principle process of energy transfer?

Answer 10

Interactions

Question 11

What does Energy Transfer lead to?

Answer 11

Ionization and Excitation

Question 12

Inelastic interactions with Nuclei produces what?

Answer 12

Bremsstrahlung x-ray

Question 13

Formula for Mean Energy of electron:

Answer 13

Eo = 2.4 MeV/cm x R50

Question 14

Formula for Most Probable E of electron:

Answer 14

Epo = C1 + C2Rp + C3Rp^2
*Rp = practical range (where electrons stop)

Question 15

Formula for E at a given depth of electron:

Answer 15

Ez = Eo x (1 - z/Rp)
z = depth

Question 16

Formula for Max/Practical Range of electron:

Answer 16

Max Range = E / 2cm

Question 17

Formula for dose at 90% isodose line for electron:

Answer 17

d90 = E / 3.2cm

Question 18

Formula for dose at 80% isodose line for electron:

Answer 18

d80 = E / 2.8cm

Question 19

For electrons, how is surface dose related to energy?

Answer 19

As E increases, surface dose increases

Question 20

For electrons, what type of E causes isodoses to “bulge out”

Answer 20

Low E e’

Question 21

An increase in FS has what effect on dose for electron treatments?

Answer 21

Dose Increases

Question 22

Formula for output factor of e’ block

Answer 22

(Dxx * Dyy)^1/2

Question 23

Formula for electron E loss

Answer 23

2MeV / cm

Question 24

Electron Characteristics in relation to E:

Answer 24

1. Surface dose increases with E
2. Dmax increases with E
3. Dmax plateau broadens with E
4. Dx increases with E
5. Slope is less steep with E

Question 25

X-Ray contamination in electrons is what type

Answer 25

bremsstrahlung

Question 26

X-Ray contamination _____ with e’ energy, by how much for 5MeV, 10MeV, and 20MeV?

Answer 26

increases;

1. 5 MeV: 1%
2. 10 MeV: 2%
3. 20 MeV: 4%

Question 27

Effects of beam obliquity for e’ beams:

Answer 27

1. Increases side scatter
2. dmax becomes shallower
3. decreased depth of penetration
4. Surface dose increases

Question 28

Characteristics of electron backscatter factor (EBF)

Answer 28

1. EBF increases with lower E

2. EBF increases with increasing Z material

Question 29

Formula for Electron Output with distance:

Answer 29

((VSD + dmax) / (VSD + dmax + gap))^2

• VSD = virtual source distance
• gap = difference of SSD and nominal, ie. if SSD = 111, then gap is 11

Question 30

What is VSD dependent on

Answer 30

1. electron E

2. Cone size

Question 31

What is the Surface dose, dmax of 6E

Answer 31

75%, 1.3cm

Question 32

What is the Surface dose, dmax of 9E

Answer 32

80%, 2.0cm

Question 33

What is the Surface dose, dmax of 12E

Answer 33

85%, 2.8cm

Question 34

What is the Surface dose, dmax of 15E

Answer 34

90%, 2.8cm

Question 35

What is the Surface dose, dmax of 18E

Answer 35

93%, 2.2cm - 3.2cm