Quiz 3

Question 1

which of the following is true regarding electron beams?

a. they are most useful for treating superifical lesions
b. they provide ecvellent skin sparing
c. they are ideal for irregular external contours
d. they dont require field shaping

Answer 1

a. they are most useful for treating superifical lesions

Question 2

when the kinetic energy of an electron is conserved, this type of collision is called

a. radiative collision
b. bremsstrahlung
c. elastic collision
d. absorbed dose

Answer 2

c. elastic collision

Question 3

the type of ineslastic collision which occurs predominantly with electrons interacting with high Z materials is called

a. ionizations
b. excitiations
c. bremsstrahlung
d. nuclear scatter

Answer 3

c. bremsstrahlung

Question 4

as a rule of thumb, approx. how much energy, in MeV, does an electron lose per centimeter of travel?

Answer 4

2

Question 5

what casues the electron energy range to broaden after exiting the bending magnent?

a. collisions with molecules in the air
b. scattering off the collimators
c. interaction with the scatering foils
d. all of the above

Answer 5

d. all of the above

Question 6

unlike photons, electrons lose energy with each interaction until they lose all of their energy. The depth at which this happens is called the

a. terminal depth
b. practical range
c. therapeutic range
d. bremmstrahlung depth

Answer 6

b. practical range

Question 7

as the electron energy increases, the surface dose will

a. decrease
b. not change
c. not enough information given
d. increase

Answer 7

d. increase

Question 8

the depth on the electron depth dose curve which represents the practical depth for clinical treatment with that electron energy is called the

a. dose calculation depth
b. bremsstrahlung
c. therapeutic range
d. dmax

Answer 8

c. therapeutic range

Question 9

for an isodose distribution perpendicular to central axis, the area of dose which is greater than 90% divded by the defined beam area on the surface is called the

a. symmetry
b. uniformity index
c. flatness
d. profile

Answer 9

b. uniformity index

Question 10

trimmer bars or collimating cones are necessary for electron beams because

a. scatter in air broadens the beam
b. they provide scater to flatten the beam
c. they define the uniformity index

Answer 10

a. scatter in air broadens the beam

Question 11

T/F: dose output increases with increasing field size for electrons until the field size increases beyond the max range of the electrons

Answer 11

true

Question 12

since electrons are scattered by air we use the distance from an effective source position to the isocenter for calculating doses at varying distances. this is called the

a. scatter SSD
b. effective SSD
c. electron SSD
d. phantom SSD

Answer 12

b. effective SSD

Question 13

how much of a margin, in cm, is typically suggested for the field sizw of an electron field in order to treat the target only with the umbra of the field?

Answer 13

2

Question 14

bolus material commonly used for electron beams in order to

a. even out the surface
b. reduce the beam penetration
c. increase the surface dose to the patient
d. all of the above

Answer 14

d. all of the above

Question 15

if the external shielding block is not thick enough for the electron energy being used, what unwanted situation may occur?

a. the electrons will all backscatter
b. the electrons will create xrays beyond the block
c. the electrons will penetrate deeper than inteneded
d. none of the answers are correct

Answer 15

b. the electrons will create xrays beyond the block

Question 16

the main magnet or primary magnet in a magnetic resonance imaging machine produces

a. radiofrequency pulses
b. secondary magnetic fields in the x, y, and z planes
c. magnetic resonance pulses
d. a strong, uniform magnetic field

Answer 16

d. a strong, uniform magnetic field

Question 17

the CT number on a CT image is related to the

a. the attenuation coefficient of tissue
b. the attenuation coeffecient of water
c. both answers are correct

Answer 17

c. both answers are correct

Question 18

when the CT couch moves longitudinally 1.0 cm per helical rotation and the bea width is 4 mm, what can be said about the data collected?

a. some of the anatomical data are collected more than once
b. not all of the anatomical data are collected

Answer 18

b. not all of the anatomical data are collected

Question 19

the diameter of the reconstructed CT image is known as the

a. CT number
b. hounsfield number
c. aperture size
d. field of view

Answer 19

d. field of view

Question 20

the intensity values of the pixels in a CT scan are determined from the attenuation coeffeicients of the tissues relative to water. this is called the

a. relative attenuation coefficient
b. CT density
c. CT number
d. hounsfield unit

Answer 20

c. CT number

Question 21

T/F: in PET the radionuclide selected is based on its bioloical uptake characteristics

Answer 21

false

Question 22

which of the following imaging modalities has the highest spatial resolution?

a. ultrasound
b. MRI
c. PET
d. CT

Answer 22

d. CT

Question 23

which of the following not NOT an advantage of digital radiography over film radiography?

a. image post processing
b. wider dynamic range
c. spatial resolution independent of pixel size
d. higher sensitivity to radiaiton

Answer 23

c. spatial resolution independent of pixel size

Question 24

image guided radiotherapy is most useful with

a. targets not well defined by current imaging technologies
b. areas of low contrast tissue
c. targets close to cirtical organs
d. all of the answers are correct

Answer 24

c. targets close to cirtical organs

Question 25

the portion of the radiographic film with which the light or xrays interact to form an image is called the

a. overcoat
b. emulsion
c. adhesive layer
d. base

Answer 25

b. emulsion

Question 26

the proton beam machine can use which of the following to create the spread out bragg peak?

a. ridge filter
b. high atomic number scattering foils
c. low atomic number modulator wheel
d. all of the above

Answer 26

d. all of the above

Question 27

high dose single fractin treatment to the brain or skull is called

a. SRS
b. FSRT
c. SBRT
d. none are correct

Answer 27

a. SRS

Question 28

which of the following will decrease morbidity for total skin electron therapy patients

a. use a beam spoiler
b. boost areas blocked by anatomy during primary treatment
c. shield the eyes and nail beds
d. all of the above

Answer 28

c. shield the eyes and nail beds

Question 29

patient motion between different fractions of radiation treatment is called _______ motion

Answer 29

interfractional

Question 30

when organ motion is accounted for during the contouring of internal structures (instead of at the time of treatent) is called

a. internal motion gating
b. integrated volume management
c. passive motion management

Answer 30

c. passive motion management