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Physic IV > Midterm > Flashcards

Midterm Flashcards

1
Q

x-ray beam quality is representative of

a. none of the answers are correct
b. the quantity of the photons
c. the number of photons
d. the penetration ability of the photon

A

d. the penetration ability of the photon

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2
Q

the term for the monoenergetic beam which matches the attenuation of a polyenergetic beam is called the

a. mean energy
b. effective energy
c. most proabable energy
d. average energy

A

b. effective energy

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3
Q

the measurement of quality most often used for x-ray beams between 50 keV and 150 keV is

a. half value layer
b. average energy
c. peak energy
d. most probable energy

A

a. half value layer

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4
Q

which is true of a polyenergetic photon beam?

a. not enough information is given
b. HVL 1 is less than HVL 2
c. HVL 1 is greater than HVL 2
d. HVL1 is equal to HVL2

A

b. HVL 1 is less than HVL 2

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5
Q

absorbed dose measuremets are restricted to

a. photons only
b. measurements in air
c. energies over 3 MeV
d. none of the answers are correct

A

d. none of the answers are correct

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6
Q

which is necessary for the Bragg-Gray relationship to exist?

a. the air cavity is in electronic equilibrium portion of the medium
b. the air cavity doesn’t change the number or distribution of electrons
c. the air cavity is tissue equivalent for the energy of the beam
d. the air cavity is larger than the range of electrons produced

A

b. the air cavity doesn’t change the number or distribution of electrons

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7
Q

what is the primary function of the build up cap for an ionization chamber?

a. to filter out low energy electrons
b. to filter out low energy photons
c. to provide electronic equilibrium
d. to prevent electrical shock from the ionization chamber

A

c. to provide electronic equilibrium

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8
Q

where is the maximum value of dose for a photon beam irradiating a medium?

a. at the surface
b. none of the answers are correct
c. at the point of electron equilibrium
d. at the point KERMA equals dose

A

c. at the point of electron equilibrium

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9
Q

which of the following is a measurement of the enrgy absorbed?

a. exposure
d. charge
c. dose
d. quality

A

c. dose

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10
Q

the SI Unit for absorded dose is Gray, is equivalent to

a. 1 erg/gram
b. 0.01 erg/gram
c. 1 Joule/kilogram
d. 0.011 Joule/gram

A

c. 1 Joule/kilogram

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11
Q

int he equation for KERMA, for phtons the quantity Etr is the sum of all the initial kinetic energies of the

a. charged particles created by uncharged particles per unit mass
b. charged particles created by uncharged radiation
c. incident photons per unit mass
d. incident photons

A

b. charged particles created by uncharged radiation

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12
Q

absorbed dose is energy ______ matter and KERMA is energy ______ matter.

A

absorbed by, released to

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13
Q

where is the maximum value of KERMA for a photon beam irradiating a medium?

a. at the point KERMA and Dose are equal
b. at the point of maximum dose
c. at the point of electronic equilibrium
d. at the surface of the medium`

A

d. at the surface of the medium`

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14
Q

the use of a flattening filer in a megavoltage radiaiton beam

a. reduces the quantity of photons
b. increases the quality of the beam
c. makes the beam profile more uniform
d. all of the answers are correct

A

d. all of the answers are correct

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15
Q

the alignment of the light field to the radiaiton field can not be measured using

a. the cnetral axis depth dose
b. the profile
c. the cross sectional isodose curve

A

a. the cnetral axis depth dose

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16
Q

the line on a two dimensional isodose distribution represent locations of

a. equal dose
b. constant energy
c. equal depth
d. maximum absorpotion

A

a. equal dose

17
Q

which of the following is true when measuring PDD?

a. the source to chamber distance is constant
b. the source to surface distance is constant
c. the chamber to isocenter distance is constant
d. the chamber depth is constant

A

b. the source to surface distance is constant

18
Q

which of the following cannot be determinedfrom the central axis depth dose curve?

a. penumbra
b. depth of maximum dose
c. relative energy of the beam
d. all fo the answers are correct

A

a. penumbra

19
Q

the difference between the geometric penumbra and dosimetric penumbra is

a. source to measurement distance
b. scatter radiation
c. radiaiton field size
d. none of the above

A

b. scatter radiation

20
Q

which properties of the human body should radiaiton measurement phantoms hae in order to more accurately represent human tissue?

a. atomic number
b. electron density
c. physical density
d. all of the answers are correct

A

d. all of the answers are correct

21
Q

a one dimensional representation of the dose distribution which is perpendicular to the central axis of the beam is called the

a. beam profile
b. penumbra
c. isodose line
d. central axis

A

a. beam profile

22
Q

The Tissue Maximum Ratio, TMR, is a special case of the

a. tissue phantom ratio
b. percent depth dose
c. tissue air ratio
d. none of the above

A

a. tissue phantom ratio

23
Q

which phantom is best used by the physicist for measuring the dosimetric parameters of a linear accelerator prior to using the machine on patients?

a. solid water phantom
b. 3D water phantom
c. anthropomorphic phantom
d. polystyrene phantom

A

b. 3D water phantom

24
Q

Which of the following would have the highest quality beam on central axis?

a. 10 MV with flattening filter
b. 10 MV without flattening filter
c. 6 MV without flattening filter
d. 6 MV with flattening filter

A

a. 10 MV with flattening filter

25
Q

the isocenter can best be described as

a. the central axis of the radiation beam
b. photon with the highest dose in the beam
c. the point in the room where the radiaiton beam is defined
d. the point in space which is the axis of all linac rotation

A

d. the point in space which is the axis of all linac rotation

26
Q

which of the following energy losses resulting from the initial ionization electrons would be included in the definition of KERMA?

a. excitations
b. ionizations
c. both are correct

A

c. both are correct

27
Q

the SI unit for KERMA is

a. rad
b. Joule
c. Gray
d. erg

A

c. Gray

28
Q

which of the following is a measure of the biological effects of radiation absorption?

a. HVL
b. exposure
c. charge collected
d. absorbed dose

A

d. absorbed dose

29
Q

bragg-gray theory states the ionization produced in a gas-filled cavity placed in a medium is related to the _____ absorbed in the surrounding medium if the cavity doesn’t alter the ______ or distribution of the electrons that would exist if there were no cavity.

a. charge, energy
b. fluence, charge
c. electrons, energy
d. energy, number

A

d. energy, number

30
Q

which of the following can be used to measure beam quality of a megavoltage photon beam?

a. TPA at 10cm
b. depth where PDD is 50%
c. PDD at 10 cm
d. all answers are correct

A

c. PDD at 10 cm

31
Q

which of the following would you expect to be the approximate dmax of a 15 MV photon beam?

a. 3.0 cm
b. 2.0 cm
c. 1.5 cm
d. 1.0 cm

A

a. 3.0 cm

32
Q

the ratio of the TMR at 20 cm divided by the TMR at 10 cm gives a number which is related to the energy of the photon beam. This ratio is call the ________ which is used to determine the ________ from a graph relating the two quantities.

A

ionization ratio

nominal accelerating potential

33
Q

what is the approximate PDD at 10 cm for a 6 MV photon beam?

a. 77%
b. 67%
c. 73%
d. 80%

A

b. 67%

34
Q

which of the following is not a reason for measuring the quality of an xray beam?

a. to determine the calibration frequency
b. to determine the ionization chamber response
c. to set up the dosimetry for planning
d. to determine the appropriate room shielding

A

a. to determine the calibration frequency

35
Q

the quality of the radiaiton beam is a measure of the photon

a. energy
b. output
c. flux
d. all of the above

A

a. energy

36
Q

which of the following is a direct measurement of absorbed dose?

a. silicon diode
b. radiographic film
c. optically stimulated luminescent dosimeter
d. thermoluminescent dosimeter
e. calorimetry

A

e. calorimetry

37
Q

which central axis measure of radiation dose will deliver a higher dose of radiaiton at 10 cm depth in a patient for the same beam on time, PDD or TMR?

why?

A

TMR

closer to beam
closer to source
no beam fall off

Physic IV (13 decks)

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