Vert Lab Homework

Question 1

when measuring PDD the radiation measured at depths beyond dmax decreases due to which of the follow? (more than one)

a. change of energy away from the central axis
b. the inverse square relationship
c. increased attenuation in the medium
d. loss of electronic equilibrium

Answer 1

b. the inverse square relationship

c. increased attenuation in the medium

Question 2

as photon energy increases the depth where dmax occurs

a. increases
b. does not change
c. moves laterally
d. decreases

Answer 2

a. increases

Question 3

T/F: as photon energy increases, the dose at the surface decreases

Answer 3

true

Question 4

T/F: the depth where the PDD is maximum ocurs where electronic equilibrium begins

Answer 4

true

Question 5

What is true about the Tissue Maximum Ratio, TMR?

a. the measurement point is at dmax in the phantom
b. the measurement is typically made at the linac isocenter
c. it is a special case of the tissue phantom ratio, TMR
d. the point of measurement is always at the same location in space
e. all of the answers are correct

Answer 5

e. all of the answers are correct

Question 6

if your chamber is reading at a SCD (source to chamber distance) of 101.5 cm is 105.0, what would be the reading be at a SCD of 72 cm?

Answer 6

208.7 cm

Question 7

if your reading at a SCD of 101.5 cm is 115.5, what would the reading be at a SCD of 130 cm?

Answer 7

70.4 cm

Question 8

as the distance between the source of radiation and the measurement device increase the quantity of radiation decreases by the inverse square relationship. this decrease in the quantity of radiation is due to:

a. the dose being distrinuted over a larger area in space
b. radiation scattered outside the treatment area
c. increased absorption of photons in air
d. decreas in the quality of the beam

Answer 8

a. the dose being distrinuted over a larger area in space

Question 9

what is true about the Tissue Max Ratio?

a. the measurement point is at dmax in the phantom
b. the measurement is typicallymade at the linac isocenter
c. it is a special case of the tissue phantom ratio
d. the point of measurement is always at the same location in space
e. all of the answers are correct

Answer 9

e. all of the answers are correct

Question 10

as the distance between the source of radiaiton and the measurement device increases the quantity of radiaiton decreases by the inverse square relationship. this descrease in the quantity of radiation is due to:

a. the dose being distributed over a larger area in space
b. radiaiton scattered outside the treatment area
c. increased absorption of photons in air
d. decrease in the quality of the beam

Answer 10

a. the dose being distributed over a larger area in space

Question 11

the fact that the radiaiton field size increases linearly with increasing SSD is an example of

a. angular dependency
b. beam divergence
c. penumbra
d. inverse square

Answer 11

b. beam divergence