fun with physics

Question 1

the depth within the body that receives the same dose of radiation

Answer 1

isodose line

Question 2

compensates for curves in the body

Answer 2

compensators

Question 3

adjusts the beam profile to reduce the dose to more sensitive parts of the body

Answer 3

wedges

Question 4

measurement made by passing a dosimeter across the beam

Answer 4

dose profile

Question 5

measure of the side to side quality of the beam; usually required to be +/- 1-2% from one side of the beam to the other

Answer 5

symmetry

Question 6

generally the max variation of the beam intensity in the central 80% of the beam; required to be +/- 2-3% across the beam

Answer 6

flatness

Question 7

the TAR at max on the CAX of the beam is referred to as what?

Answer 7

Backscatter factor

Question 8

the region between the patient’s skin and the max is referred to as what?

Answer 8

dose build up region

Question 9

the absorbed dose at a given depth expressed as a % of the absorbed dose at a reference depth on the CAX of the field

Answer 9

PDD

Question 10

PDD is dependent on what 5 variables?

Answer 10

energy, field size, SSD, depth, composition of the irradiated medium

Question 11

does PDD increase or decrease with increased SSD

Answer 11

increase

Question 12

does PDD increase or decrease with increasing field size

Answer 12

increase

Question 13

does PDD increase or decrease with increased depth

Answer 13

decrease

Question 14

what is dose in tissue/ dose at d-max in a phantom

Answer 14

TMR

Question 15

what 3 factors is TMR dependant

Answer 15

depth, energy, field size

Question 16

what is used to calculate changes in PDD

Answer 16

Mayneord’s Factor

Question 17

what is dose in tissue/dose in air?

Answer 17

TAR

Question 18

ratio of dose on the CAX at d-max to dose at the same point in air

Answer 18

BSF

Question 19

BSF and __ at dmax are the same

Answer 19

TAR

Question 20

is TMR dependent on SSD

Answer 20

no

Question 21

Which of the following is true when measuring Percent Depth Dose (PDD)?
A. The Source to Chamber distance is constant.
B. The chamber to Axis distance is constant.
C. The Source to Surface distance is constant.
D. The chamber depth is constant.

Answer 21

C. the source to surface distance is constant

Question 22

Which of the following is most often used to measure beam quality of a megavoltage photon beam?
A. PDD at 10 cm
B. TPR ratio at 20cm and 10 cm C. Half Value Layer
D. Depth where PDD is 50%
E. a and b only.

Answer 22

E. A and B only

Question 23

at approximately what energy does backscatter factor become no longer meaningful?

Answer 23

10 MV

Question 24

The reference depth for the Tissue Phantom Ratio, TPR, is:
A. dmax. 
B. 5 cm. 
C. 10 cm. 
D. dependent on measurement choice

Answer 24

D. dependent on measurement choice

Question 25

what is D-max

Answer 25

depth of the max dose

Question 26

where are PDD 10 and TPR 20/10 measured

Answer 26

central axis

Question 27

with TPR does the SSD change

Answer 27

yes

Question 28

does scatter increase or decrease with field size

Answer 28

increase

Question 29

with TAR, is the SCD constant? what about the measurement point?

Answer 29

with TAR the SCD and measurement point are constant

Question 30

TAR varies with what 3 things

Answer 30

depth, field size, energy

Question 31

dose at a point divided by the dose at d-max

Answer 31

depth dose

Question 32

does depth dose increase or decrease with increasing field size

Answer 32

increase

Question 33

will a shorter SSD make the depth dose go up or down

Answer 33

down

Question 34

two measurements are made, one in phantom and one in air at the same time

Answer 34

TAR

Question 35

a variation of TPR but the reference depth is usually taken to be D-max

Answer 35

TMR

Question 36

a ratio of dose in a phantom divided by the dose in a phantom at a reference depth

Answer 36

TPR

Question 37

what parameter is used to calculate the scatter dose component of a blocked field

Answer 37

scatter maximum ratio

Question 38

Which of the following is true when measuring TPR? A. The Source to Chamber distance is constant. B. The chamber to surface distance is constant. C. The Source to Surface distance is constant. D. The chamber depth is constant.

Answer 38

A. the source to chamber distance is constant

Question 39

what is penumbra?

Answer 39

area or region at the beams edge where the radiation. intensity falls to 0

Question 40

when treating a patient with skin cancer and using electrons, which does the electron use, a scattering foil or a flattening filter?

Answer 40

scattering foil