Q 36-70

Question 1

If an ion chamber is not sealed, the chamber reading for a given exposure will increase as the temperature _____ or the pressure _____.
A. increases; increases
B. increases; decreases
C. decreases; increases
D. decreases; decreases

Answer 1

C. decreases; increases

Question 2

According to the AAPM Task Group 51 protocol, plane-parallel chambers must be used for _____ beams with incident energies of _____ or less.
A. photon; 6 MV
B. photon; 10 MV
C. electron; 6 MeV
D. electron; 12 MeV
E. electron; 20 MeV

Answer 2

C. electron; 6 MeV

Question 3

An ion chamber scanning vertically in a water tank measures which of the following parameters for an electron treatment beam?
A. backscatter factor
B. tissue phantom ratio
C. tissue maximum ratio
D. percent depth ionization
E. percent depth dose

Answer 3

D. percent depth ionization

Question 4

What is physically happening when an optically stimulated luminescent dosimeter (OSLD) emits
light?
A. An electron falls into an electron trap.
B. An electron escapes from an electron trap.
C. An electron travels freely through the valence band.
D. An electron travels freely through the conduction band.
E. None of the above is true.

Answer 4

B. An electron escapes from an electron trap.

Question 5

Of the following, a _____ is an absolute dosimeter.
A. free-air ionization chamber
B. calorimeter
C. ferrous sulfate (Fricke) dosimeter
D. All of the above are true.
E. None of the above is true.

Answer 5

D. All of the above are true.

Question 6

Of the following parameters, _____ does NOT influence the physical penumbra.
A. depth
B. source-to-surface distance (SSD)
C. source-to-diaphragm distance (SDD)
D. beam energy
E. gantry angle

Answer 6

E. gantry angle

Question 7

The average energy of a linac’s 15-MV photon beam at the surface of the patient is _____.
A. 3 MeV
B. 5 MeV
C. 7.5 MeV
D. 10 MeV
E. 15 MeV

Answer 7

B. 5 MeV (30% of maximum dose)

Question 8

All of the following statements describe an aspect of MV photon beam depth dose distributions, EXCEPT which one.

A. Kerma is maximum at the surface and decreases with depth due to attenuation.
B. Electrons are liberated when the photon beam interacts with the patient’s tissue.
C. High-energy electrons deposit their energy downstream of where they were liberated.
D. At depths greater than the maximum range of the electrons, dose decreases due to attenuation.
E. The depth of maximum dose decreases with increasing energy.

Answer 8

E. The depth of maximum dose decreases with increasing energy.

Question 9

A patient is being treated with a four-field box with 6-MV x-ray beams equally weighted to the prescription point. At setup it is noted that the AP beam’s depth to the prescription point is 2 cm less than expected, and the depths of the other 3 beams are unchanged. What is the approximate dose difference at the prescription point?

A. 10% less than planned
B. 5% less than planned
C. 2% less than planned
D. 2% more than planned
E. 5% more than planned

Answer 9

D. 2% more than planned

Question 10

For an MV photon treatment on a patient with a bolus placed on top of an ill-fitting thermoplastic immobilization mask, as an air gap between the bolus on the mask and the patient surface increases, the depth of maximum dose will _____ and the surface dose will _____.

A. decrease; decrease
B. increase; decrease
C. decrease; increase
D. increase; increase
E. remain the same; decrease

Answer 10

B. increase; decrease

Question 11

An advantage of flattening filter free (FFF) treatment beams is _____.
A. increased head scatter
B. reduced surface dose
C. reduced treatment time
D. they are more difficult to model the beam in a treatment planning system
E. All of the above are true.

Answer 11

C. reduced treatment time

Question 12

7. The water-equivalent path length for an MV photon beam that has traversed 4 cm of soft tissue and 6 cm of lung issue is _____ a beam that has traversed 10 cm of soft tissue.

A. greater than
B. less than
C. equal to
D. This cannot be determined from the information given.

Answer 12

B. less than

Question 13

A patient is treated with an isocentric AP/PA setup on a linac. The anterior SSD is 86 cm, and the
posterior SSD is 92 cm. The patient’s AP/PA separation is _____.
A. 14 cm
B. 16 cm
C. 22 cm
D. 28 cm
E. This cannot be determined from the information given.

Answer 13

C. 22 cm

Question 14

The collimator setting is the field length and width as defined at the level of the _____.
A. patient entrance surface
B. patient exit surface
C. jaws in the linac head
D. multileaf collimator in the linac head
E. isocenter

Answer 14

E. isocenter

Question 15

The field size is set to 16.0 × 16.0 cm2 on a linac with 100-cm SAD. What is the field size measured on the patient surface if the patient is set to 130-cm SSD?

A. 12.3 × 12.3 cm2
B. 16.1 × 16.1 cm2
C. 20.8 × 20.8 cm2
D. 23.2 × 23.2 cm2
E. 29.6 × 29.6 cm2

Answer 15

C. 20.8 × 20.8 cm2

Question 16

A linac is calibrated to give 1.00 cGy/MU to dmax for a 10 × 10 cm2 field at 100 cm SSD. How many MU are needed to deliver 200 cGy to depth if the PDD is 50% for a 10 × 10 cm2 field at 100 cm SSD?
A. 100 MU
B. 200 MU
C. 400 MU
D. 600 MU
E. 800 MU

Answer 16

C. 400 MU

Question 17

The percent depth dose (PDD) for an MV photon beam decreases with increasing _____.
A. field size
B. depth beyond dmax
C. energy
D. SSD
E. All of the above are true.

Answer 17

B. depth beyond dmax

Question 18

Which of the following point locations is appropriate to use when performing a verification that
the planned MU are correct?
A. out-of-field point
B. point near the field edge
C. point near the inhomogeneity interface
D. point on the patient surface
E. None of the above is true.

Answer 18

E. None of the above is true.

Question 19

The wedge transmission factor (WTF) is 0.90. The MU setting for an open beam is 150. The MU
setting for the same dose on the central axis when using the wedge would be _____.
A. 135 MU
B. 150 MU
C. 167 MU
D. 180 MU
E. 240 MU

Answer 19

C. 167 MU

Question 20

A patient is being treated to a dose of 10 Gy to a depth of 10 cm with a 6-MV posterior photon
beam in an SAD setup. The spinal cord is located upstream of the target at a 4-cm depth. The
TMRs are 0.770 and 0.946 for 10 cm and 4 cm depths, respectively. What is the dose to the spinal
cord?
A. 8.0 Gy
B. 10.8 Gy
C. 12.2 Gy
D. 13.9 Gy
E. This cannot be determined using the information given

Answer 20

D. 13.9 Gy

Question 21

Considering an AP/PA photon dose distribution prescribed to midplane depth, the hot spot _____.
A. increases when changing from a 100 SAD to a 100 SSD setup
B. decreases for increasing beam energy
C. increases as the patient thickness decreases
D. All of the above are true.
E. None of the above is true.

Answer 21

B. decreases for increasing beam energy

Question 22

External beam prostate treatments should use photon energies less than or equal to 10 MV for
patients with a pacemaker because with higher energies _____.
A. the fields will be too large and will include the pacemaker
B. photons scattered from the treatment fields would give more than 5 Gy to the pacemaker
C. photons scattered from the treatment head would give more than 5 Gy to the pacemaker
D. stray neutrons that penetrate the linac shielding can trigger pacemaker irregularities
E. prostate cancer is always treated with lower-energy photons or brachytherapy

Answer 22

D. stray neutrons that penetrate the linac shielding can trigger pacemaker irregularities

Question 23

All of the following statements regarding electron scattering foils in the linac are true, EXCEPT
for which one?
A. Modern linacs typically use dual scattering foils.
B. Foils use a combination of high-Z and low-Z materials to increase scattering but also
minimize bremsstrahlung production.
C. In electron mode, the target and flattening filter are rotated out of the beam path, and the
scattering foil is rotated in.
D. The scattering foil is typically below the monitor chamber in the linac head.
E. There are multiple scattering foils in the head of the machine in order to handle the range
of deliverable electron energies.

Answer 23

D. The scattering foil is typically below the monitor chamber in the linac head.

Question 24

Tungsten eye shields effectively protect the lens and eye for _____.
A. Co-60 teletherapy
B. megavoltage x-ray teletherapy
C. megavoltage electron teletherapy
D. eye plaque brachytherapy
E. All of the above are true.

Answer 24

C. megavoltage electron teletherapy

Question 25

_____ is the most appropriate electron energy to cover a target at depth of 3.5 cm when prescribing
to the 90% isodose line.
A. 6 MeV
B. 9 MeV
C. 12 MeV
D. 15 MeV
E. 18 MeV

Answer 25

C. 12 MeV

Question 26

When an electron beam enters a surface obliquely, _____ increases relative to perpendicular
incidence.
A. surface dose
B. depth of Dmax
C. depth of the distal D90%
D. All of the above are true.
E. None of the above is true.

Answer 26

A. surface dose

Question 27

When the electron field size is smaller than the practical range of the electron beam, all of the
following are true EXCEPT for which statement?
A. The dose rate decreases.
B. Dmax moves closer to the surface.
C. The PDD curve changes.
D. Dose rate remains constant with the field shape

Answer 27

D. Dose rate remains constant with the field shape

Question 28

In total skin electron therapy, the gantry is angled such that the central axis is above and below the
patient at extended SSD. This is done to _____.
A. limit exposure to contamination from bremsstrahlung x-rays
B. obviate the need for a beam spoiler
C. better cover folds of the skin
D. All of the above are true.
E. None of the above is true

Answer 28

A. limit exposure to contamination from bremsstrahlung x-rays

Question 29

Order the following materials from LEAST to MOST production of backscattered electrons for a
9-MeV electron beam.
A. bolus, aluminum, lead
B. lead, bolus, aluminum
C. aluminum, lead, bolus
D. lead, aluminum, bolus
E. bolus, lead, aluminum

Answer 29

A. bolus, aluminum, lead

Question 30

The cumulative dose for an implanted cardiac device (ICD), according to AAPM Task Group 203,
should be kept to less than or equal to _____ or the manufacturer’s recommended dose threshold if
higher.
A. 10 cGy
B. 100 cGy
C. 200 cGy
D. 500 cGy
E. 1000 cGy

Answer 30

D. 500 cGy

Question 31

According to AAPM Task Group 142, the tolerance for the daily check of the linac optical distance
indicator (ODI) is _____.
A. 0.5 mm
B. 1 mm
C. 2 mm
D. 3 mm
E. 5 mm

Answer 31

C. 2 mm

Question 32

According to AAPM Task Group 142, the tolerance for the monthly check of the jaw position
indicators is _____ mm for symmetric and _____ mm for asymmetric jaw settings.
A. 0.5; 0.5
B. 1; 1
C. 1; 2
D. 2; 1
E. 2; 2

Answer 32

D. 2; 1

Question 33

According to AAPM Task Group 142, the coincidence of a linac’s imaging system isocenter and
treatment isocenter should be within _____ mm for an SRS/SBRT machine.
A. 0.25
B. 0.5
C. 1
D. 1.5
E. 2

Answer 33

C. 1