Question 1

Calculate the PDD of depth (d)if the dose at Dmax is 180 cGy and the dose at d is 127 cGy.

Accepted Answer

A)  47% 
B)  70.6% 
C)  56% 
D)  75% 
A)  47% 
B)  70.6% 
C)  56% 
D)  75% B

Question 2

What is a TAR at the depth of Dmax used to correct for scatter of dose called?

Accepted Answer

A)  Scatter-air ratio 
B)  Tissue-phantom ratio 
C)  Backscatter factor 
D)  Mayneord's F factor 
A)  Scatter-air ratio 
B)  Tissue-phantom ratio 
C)  Backscatter factor 
D)  Mayneord's F factor C

Question 3

As the SSD increases, the PDD does what?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect A

Question 4

What is the patient's depth from the AP if the source-axis distance (SAD)is 100 cm and source-skin distance (SSD)is 91 cm?

Accepted Answer

A)  8 cm 
B)  9 cm 
C)  10 cm 
D)  11 cm 
A)  8 cm 
B)  9 cm 
C)  10 cm 
D)  11 cm

Question 5

Which of the following does not apply to "absorbed dose?"

Accepted Answer

A)  Energy deposited at a point 
B)  Measured in Gray 
C)  Measured in air 
D)  Can measure absorbed dose using ionization chambers 
A)  Energy deposited at a point 
B)  Measured in Gray 
C)  Measured in air 
D)  Can measure absorbed dose using ionization chambers

Question 6

Which of the following is the equivalent square of a rectangular field of 20 × 10?

Accepted Answer

A)  12 × 12 
B)  15 × 15 
C)  11.5 × 11.5 
D)  13.3 × 13.3 
A)  12 × 12 
B)  15 × 15 
C)  11.5 × 11.5 
D)  13.3 × 13.3

Question 7

As the energy increases, the tissue-air ratio does which of the following?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect

Question 8

A tray holding custom blocks is measured as 97 cGy, and the dose without the tray is 100 cGy.What is the tray transmission factor?

Accepted Answer

A)  1.03 
B)  0.97 
C)  1.00 
D)  Not enough information to determine 
A)  1.03 
B)  0.97 
C)  1.00 
D)  Not enough information to determine

Question 9

As the field size increases, the PDD does what?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect

Question 10

A patient is treated on a 6-MV accelerator; field size is 10 × 12 cm and depth of tumor is 6 cm.What is the PDD?

Accepted Answer

A)  83.02 
B)  83.18 
C)  83.0 
D)  83.2 
A)  83.02 
B)  83.18 
C)  83.0 
D)  83.2

Question 11

A wedge filter is used to alter the isodose distribution on an anterior chest field.The monitor units setting must be ___________ to account for the wedge filter in the field.

Accepted Answer

A)  increased 
B)  decreased 
C)  unchanged 
A)  increased 
B)  decreased 
C)  unchanged

Question 12

Absorbed dose at a given depth divided by the dose in air dose at a fixed reference is the definition of which of the following?

Accepted Answer

A)  TAR 
B)  TMR 
C)  TPR 
D)  PDD 
A)  TAR 
B)  TMR 
C)  TPR 
D)  PDD

Question 13

Find the PDD at 19 cm of an 18-MV beam of radiation that has a 12 × 12 cm treatment field.

Accepted Answer

A)  56% 
B)  55.6% 
C)  53.7% 
D)  51.7% 
A)  56% 
B)  55.6% 
C)  53.7% 
D)  51.7%

Question 14

As the depth increases, what happens to the PDD?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect

Question 15

Methods of obtaining dose uniformity across field junctions include which of the following?
I.Dosimetric isodose matching
II.Separated fields
III.Junction shift
IV.Half beam blocking
V.Geometric matching

Accepted Answer

A)  I, II, III, and V 
B)  I, III, IV, and V 
C)  II, III, IV, and V 
D)  III, IV, and V 
A)  I, II, III, and V 
B)  I, III, IV, and V 
C)  II, III, IV, and V 
D)  III, IV, and V

Question 16

As a field size increases from the standard established, the output factor for a treatment machine will do what?

Accepted Answer

A)  Increase 
B)  Decrease 
C)  Remain the same 
A)  Increase 
B)  Decrease 
C)  Remain the same

Question 17

As the field size increases, the tissue-air ratio does what?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect

Question 18

Find the PDD at 10 cm of a 6-MV beam of radiation that has a 5 × 5 cm treatment field.

Accepted Answer

A)  68% 
B)  64.1% 
C)  65.1% 
D)  62.8% 
A)  68% 
B)  64.1% 
C)  65.1% 
D)  62.8%

Question 19

As the source-skin distance increases, what happens to the tissue-air ratio?

Accepted Answer

A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect 
A)  Increases 
B)  Decreases 
C)  Remains the same 
D)  No effect

Question 20

Find the PDD at 3.5 cm of an 18-MV beam of radiation that has a 23 × 15 cm treatment field.

Accepted Answer

A)  99.8% 
B)  98% 
C)  100% 
D)  98.8% 
A)  99.8% 
B)  98% 
C)  100% 
D)  98.8%

Exam 23: Photon Dosimetry Concepts and Calculations

Calculate the PDD of depth (d)if the dose at Dmax is 180 cGy and the dose at d is 127 cGy.

What is a TAR at the depth of Dmax used to correct for scatter of dose called?

As the SSD increases, the PDD does what?

What is the patient's depth from the AP if the source-axis distance (SAD)is 100 cm and source-skin distance (SSD)is 91 cm?

Which of the following does not apply to "absorbed dose?"

Which of the following is the equivalent square of a rectangular field of 20 × 10?

As the energy increases, the tissue-air ratio does which of the following?

A tray holding custom blocks is measured as 97 cGy, and the dose without the tray is 100 cGy.What is the tray transmission factor?

As the field size increases, the PDD does what?

A patient is treated on a 6-MV accelerator; field size is 10 × 12 cm and depth of tumor is 6 cm.What is the PDD?

A wedge filter is used to alter the isodose distribution on an anterior chest field.The monitor units setting must be ___________ to account for the wedge filter in the field.

Absorbed dose at a given depth divided by the dose in air dose at a fixed reference is the definition of which of the following?

Find the PDD at 19 cm of an 18-MV beam of radiation that has a 12 × 12 cm treatment field.

As the depth increases, what happens to the PDD?

Methods of obtaining dose uniformity across field junctions include which of the following? I.Dosimetric isodose matching II.Separated fields III.Junction shift IV.Half beam blocking V.Geometric matching

As a field size increases from the standard established, the output factor for a treatment machine will do what?

As the field size increases, the tissue-air ratio does what?

Find the PDD at 10 cm of a 6-MV beam of radiation that has a 5 × 5 cm treatment field.

As the source-skin distance increases, what happens to the tissue-air ratio?

Find the PDD at 3.5 cm of an 18-MV beam of radiation that has a 23 × 15 cm treatment field.

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