Question 1

Using the 6-MV PDD chart, what is the dose at 10 cm if the dose at Dmax is 300 cGy per day on a 6-MV beam for a field size of 15 × 18?

Accepted Answer

A)  205 cGy 
B)  210 cGy 
C)  215 cGy 
D)  225 cGy

Question 2

Absorbed dose at depth × 100% = absorbed dose at Dmax is the definition of which of the following?

Accepted Answer

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

Question 3

As the energy increases, what happens to the PDD?

Accepted Answer

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

Question 4

The intensity of a radiation beam is measured at 10 mR/hr at a distance of 20 cm.What will be the intensity of this beam at 30 cm?

Accepted Answer

A)  22.5 mR/hr 
B)  4.44 mR/hr 
C)  6.67 mR/hr 
D)  15 mR/hr

Question 5

Which of the following are adjacent fields that match on the surface and have an overlap at depth due to divergence?

Accepted Answer

A)  Separated fields 
B)  Abutted fields 
C)  Half beam blocking fields 
D)  Geometric matching

Question 6

A patient is being treated on the 18-MV beam to a PA spine at a depth of 10 cm.The collimator setting is 10 × 13 with no blocks.The dose is 300 cGy per fraction.What is the dose delivered to Dmax?

Accepted Answer

A)  375 cGy 
B)  240 cGy 
C)  400 cGy 
D)  300 cGy

Question 7

A patient is treated using two superiorly/inferiorly adjacent fields.The collimator setting for the superior field is 10 cm wide by 13 cm long.The collimator setting for the inferior field is 20 cm wide by 35 cm long.Both fields are treated at 100 cm SSD.Calculate the gap at the skin surface if the fields abut at a depth of 5 cm.

Accepted Answer

A)  1.5 
B)  1.2 
C)  2.0 
D)  1.0

Question 8

The intensity of a radioactive beam is measured at a distance of 100 cm and found to be 250 mR/min.What will the intensity of this beam be at 105 cm?

Accepted Answer

A)  226.8 mR/min 
B)  238.1 mR/min 
C)  262.5 mR/min 
D)  275.6 mR/min

Question 9

What is the patient separation if depth from the anterior posterior (AP)is 9 cm and depth from posterior anterior (PA)is 11 cm?

Accepted Answer

A)  18 cm 
B)  19 cm 
C)  20 cm 
D)  21 cm

Question 10

A patient is being treated on the 18-MV beam to an AP/PA stomach (midline).The collimator setting is 12 × 12 with no blocks.The dose is 4400 cGy/22 fractions.The separation is 24 cm.The cord is 4 cm from the PA.What dose is delivered to the spinal cord?

Accepted Answer

A)  206.4 cGy 
B)  180 cGy 
C)  220 cGy 
D)  133.7 cGy

Question 11

The physician prescribes the AP/PA field to be weighted 3:1 for the posterior field.How much dose is coming from the AP and the PA if total dose prescribed is 200 cGy?

Accepted Answer

A)  AP = 50 cGy, PA = 150 cGy 
B)  AP = 75 cGy, PA = 125 cGy 
C)  AP = 150 cGy, PA = 50 cGy 
D)  AP = 175 cGy, PA = 25 cGy

Question 12

What is the depth from the PA if the SAD is 100 cm and the SSD is 89 cm?

Accepted Answer

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

Question 13

Mayneord F factor is used in which of the following?

Accepted Answer

A)  Isocentric setups when distance is increased 
B)  Isocentric setups when field size changes 
C)  SSD setups when field size changes 
D)  SSD setups when distance increases

Question 14

Which of the following defines Dmax?

Accepted Answer

A)  Build-up region 
B)  Depth of maximum equilibrium 
C)  Depth of dose deposited per unit of time 
D)  Dose scatter to surface

Question 15

A patient is being treated on the 6-MV beam to an opposed lateral whole brain (midline).The collimator setting is 14 × 18 with no blocks.The dose is 4000 cGy/20 fractions.The separation is 22 cm.What is the dose delivered to Dmax?

Accepted Answer

A)  200 cGy 
B)  212 cGy 
C)  150 cGy 
D)  61.9 cGy

Question 16

Find the skin gap necessary to match two symmetric ports at midline that are 21 and 37 cm in length.Assume the midline depth is 13 cm and both ports are treated at 100 cm SAD.

Accepted Answer

A)  1.53 
B)  3.6 
C)  2.5 
D)  3.77

Question 17

Calculate the PDD of depth (d)if the dose at Dmax is 250 cGy and the dose at d is 231 cGy.

Accepted Answer

A)  70% 
B)  75% 
C)  85.2% 
D)  92.4%

Question 18

A patient is treated on a 6-MV machine at 100 cm SSD.The collimator setting is 15 × 15.There is no blocking used for this treatment.The prescription states that a dose of 3000 cGy is to be delivered to a depth of 3 cm in 10 fractions using a posterior treatment field using the nonisocentric method of calculation.The patient central axis separation is 20 cm.What is the MU setting for the treatment? Reference dose rate (RDR)for a 15 cm equivalent square is 0.993 cGy/MU.

Accepted Answer

A)  315 
B)  321 
C)  319 
D)  317

Question 19

Which of the following is the equivalent square of rectangular field of 10 ´ 15?

Accepted Answer

A)  12 × 12 
B)  3.6 × 3.6 
C)  11.5 × 11.5 
D)  13 × 13

Exam 23: Photon Dosimetry Concepts and Calculations