TAR TMR

Question 1

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

Answer 1

BSF (BACK SCATTER FACTOR)

Question 2

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

Answer 2

Dose Build-up Region

Question 3

The absorbed dose at a given depth expressed as a % of the absorbed dose at a reference depth (i.e. d-max) on the CAX of the field

Answer 3

PDD

Question 4

PDD is dependent on what 5 variables?

Answer 4

1. Energy
2. Field Size
3. SSD
4. Depth
5. Composition of the irradiated medium

Question 5

Does PDD increase or decrease with increasing SSD?

Answer 5

Increase

Question 6

Does PDD increase or decrease with increasing field size?

Answer 6

Increase

Question 7

Does PDD increase or decrease with increasing depth?

Answer 7

Decrease

Question 8

What is dose in tissue / dose at d-max in a phantom?

Answer 8

TMR

Question 9

What 3 factors is TMR dependent on?

Answer 9

1. Depth
2. Energy
3. Field Size

Question 10

What is used to calculate changes in PDD?

Answer 10

Mayneord’s Factor

Question 11

What is dose in tissue / dose in air?

Answer 11

TAR

Question 12

Ratio of dose on the CAX at d-max to dose at the same point in air(dose at d-max / dose in air)

Answer 12

BSF (Back Scatter Factor)

Question 13

BSF and _____ at Dmax are the same.

Answer 13

TAR

Question 14

Is TMR dependent on SSD?

Answer 14

No

Question 15

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 15

C. The Source to Surface distance is constant.

Question 16

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 16

E. a and b only.

Question 17

If the PDD at 10 cm is 80% at 100 cm SSD, what would the PDD be at 10 cm if the SSD is changed to 80 cm? (dmax = 3.0 cm)

Use Mayneord Factor

Answer 17

77.6

Question 18

At approximately what energy does the Backscatter Factor become no longer meaningful?
A. 6 MV
B. 10 MV
C. 12 MV
D. 18 MV
E. 24 MV

Answer 18

B. 10 MV

Question 19

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

Answer 19

D. dependent on measurement choice.

Question 20

What is TPR 20/10 a measure of? Is it dependent on or independent of the electron contamination in the incident beam?

Answer 20

Independent of the electron contamination in the incident beam

Question 21

What is PDD 10?

Answer 21

PDD at 10cm depth

Question 22

What is d-max?

Answer 22

Depth of the maximum dose

Question 23

Where are PDD10 and TPR20/10 measured (what part of the beam)?

Answer 23

On the central axis of the boom

Question 24

With TPR, does the SSD change?

Answer 24

Yes, SSD changes to change depth

Question 25

Does scatter increase or decrease with field size?

Answer 25

Increase

Question 26

With TAR, is the SCD constant? What about the measurement point?

Answer 26

With TAR, the SCD (source to chamber distance) and measurement point are constant

Question 27

TAR varies with what 3 things?

Answer 27

1. Depth
2. Field Size
3. Energy

Question 28

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

Answer 28

Depth dose