Dose Calculation and Verification

Question 1

how is beam energy determined?

Answer 1

by the depth of the tumor and the separation of the patient

Question 2

photon beams penetrate __more//less__ than electron beams

Answer 2

MORE

Question 3

PDD (Percent Depth Dose) at the patient’s skin surface is around ___%

Answer 3

30%

Question 4

electron beams are used for ______ tumors

Answer 4

superficial

Question 5

the PDD at the patient’s skin surface for electron beams is about __-__%

Answer 5

80-90%

Question 6

electron treatments are usually prescribed to the ___-___% isodose line

Answer 6

80-90%

Question 7

general rule for electrons:

MeV is about __x the max depth of the tumor

Answer 7

3x

Question 8

______________ is used to find the area of IRREGULARLY shaped fields

Answer 8

Clarkson Integration

Question 9

T/F:

Clarkson Integration takes scatter from the blocked area into consideration for calculations

Answer 9

TRUE

Question 10

what does SAR stand for?

Answer 10

Scatter Air Ratio

Question 11

what is the main cause of collimator scatter?

Answer 11

photon scatter within the gantry head

Question 12

a bigger field size creates __more//less__ scatter

Answer 12

MORE

Question 13

photon scatter mostly occurs with what type of FILTER?

Answer 13

flattening filter

Question 14

____ scatter = scatter that happens within the patient or phantom

Answer 14

phantom scatter

Question 15

phantom scatter can or cannot be directly measured?

Answer 15

cannot be directly measured

Question 16

both _____ factor and ____ ____ factor compare the dose rate in free space to the dose rate within a phantom at dmax

Answer 16

backscatter factor (BSF)

peak scatter factor (PSF)

Question 17

fill in the blanks with –> BSF (backscatter factor) and PSF (peak scatter factor)

_____ is used for low-energy beams

____ is used for high energy beams ABOVE 4 MV

Question 18

what scatter factor is used for energy beams above 4 MV?

Answer 18

peak scatter factor (PSF)

Question 19

________ = the depth where electronic equilibrium is reached and 100% dose is delivered

Answer 19

dmax

Question 20

the dmax for higher energies is ___deeper//more superficial____

Answer 20

DEEPER

Question 21

as PHOTON energy increases, what happens with skin sparring?

Answer 21

skin sparring increases

Question 22

_______ = ratio that compares the absorbed dose at a depth to the absorbed dose at a specific reference dose (dmax)

Answer 22

PDD (percent depth dose)

Question 23

when is PDD used/calculated?

Answer 23

only used to calculate MU in SSD treatments

Question 24

what are the 4 components PDD changes with?

Answer 24

energy
depth
field size
SSD

Question 25

an increase in ____, ____ ____, and _____ cause the PDD to increase

Answer 25

energy, field size, SSD

Question 26

PDD and field size have a direct or indirect relationship?

Answer 26

DIRECT

-increase of FS causes an increase of PDD due to more scatter (direct relationship)

Question 27

PDD __decreases//increases___ as the SSD increases

Answer 27

increases

Question 28

depth and PDD have an direct or indirect relationship?

Answer 28

INDIRECT /”inverse”

-as the depth within the patient increase PAST dmax, the PDD decreases

Question 29

what equation makes up for the change in dose at different depths of the CAX (central axis) due to the inverse square law

Answer 29

Mayneord F factor