Q 106-140

Question 1

When optimizing a multi-arc VMAT plan, an achievable dose gradient between the target and a
nearby critical organ at risk is on the order of _____%/mm.
A. 0.05
B. 0.1
C. 1
D. 10
E. 50

Answer 1

D. 10

Question 2

The dose uniformity to the patient _____ if an extended distance total body irradiation (TBI)
treatment is moved closer to the linac, e.g., due to a move from a large vault to a small vault.
A. increases
B. decreases
C. remains the same
D. It could be better or worse depending on other parameters.

Answer 2

B. decreases

Question 3

The advantage of using a bilateral beam arrangement over an AP/PA beam arrangement for total
body irradiation (TBI) is _____.
A. the arms partially shield the lungs
B. more uniform dose to the patient
C. increased need for tissue compensation
D. All of the above are true.
E. None of the above is true.

Answer 3

A. the arms partially shield the lungs

Question 4

A radionuclide injection used to treat bone metastasis from prostate cancer is \_\_\_\_\_.
A. Ir-192
B. Pd-103
C. Ra-223
D. I-125
E. I-131

Answer 4

C. Ra-223

Question 5

Which of the following intraoperative radiotherapy (IORT) delivery methods will typically result
in the greatest depth of penetration and best dose homogeneity in the treatment area?
A. electrons
B. HDR afterloader
C. kilovoltage photons
D. All of the above are similar

Answer 5

A. electrons

Question 6

A cyclotron bombards stable nuclei with protons, typically producing \_\_\_\_\_ radioisotopes that
decay via \_\_\_\_\_.
A. short-lived; β–
 decay
B. short-lived; positron emission
C. long-lived; β–
 decay
D. long-lived; positron emission
E. long-lived; α decay

Answer 6

B. short-lived; positron emission

Question 7

_____ is typically prioritized during SBRT treatment planning.
A. Rapid dose fall-off outside of the PTV
B. Dose homogeneity within the PTV
C. Limiting the number of treatment beams (or degrees of arc)
D. Ensuring sufficient margin in the beam’s-eye view between the PTV and the edge of the
field
E. All of the above are true.

Answer 7

A. Rapid dose fall-off outside of the PTV

Question 8

Performing cranial SRS treatment planning directly on an MRI scan, rather than a CT scan, has the
DISADVANTAGE of _____.
A. inferior visualization of soft tissue targets
B. inability to localize target with sub-millimeter precision
C. increasing uncertainty in image registration for target delineation
D. lack of heterogeneity corrections for dose calculations
E. All of the above are true.

Answer 8

D. lack of heterogeneity corrections for dose calculations

Question 9

Consider two linac-based SBRT plans, each normalized such that 100% corresponds to the dose to
the isocenter in the center of the target. Plan A is prescribed 21 Gy to the 90% isodose line. Plan B
is prescribed 18 Gy to the 80% isodose line. Which of the following is FALSE?
A. The hot spot for Plan A is greater than that of Plan B.
B. Outside the target, the dose for plan B will fall off faster than for plan A.
C. Plan B has a hot spot of 22.5 Gy.
D. The volume receiving 20 Gy will be greater in Plan A.
E. The hot spot for both plans is a point corresponding to the 100% isodose

Answer 9

B. Outside the target, the dose for plan B will fall off faster than for plan A.

Question 10

For SRS, the Conformity Index was defined by the RTOG as a ratio of the _____, and the desired
ratio is _____.
A. volume covered by the prescribed dose to the target volume; less than 1
B. volume covered by the prescribed dose to the target volume; between 1 and 1.5
C. volume covered by the prescribed dose to the target volume; between 2 and 2.5
D. target volume to the volume covered by the prescribed dose; between 1 and 2
E. target volume to the volume covered by the prescribed dose; between 2 and 2.5

Answer 10

B. volume covered by the prescribed dose to the target volume; between 1 and 1.5

Question 11

When developing end-to-end tests for SRS/SBRT commissioning, which aspect of the treatment
process should be considered?
A. simulation
B. treatment planning
C. treatment delivery
D. All of the above are true.
E. None of the above is true.

Answer 11

D. All of the above are true.

Question 12

The anisotropy of the dose distribution around brachytherapy line sources is caused by _____.
A. the inverse square law
B. radioactive decay
C. uncertainty of source calibration
D. attenuation and scattering in the source and encapsulation
E. the photon spectrum of the source

Answer 12

D. attenuation and scattering in the source and encapsulation

Question 13

An HDR plan was created using a 3-cm-diameter vaginal cylinder. A plan using a 3.5-cm-diameter
cylinder but normalized to deliver the same dose to the reference point 5 mm from the cylinder
surface would deliver _____.
A. the same dose to the cylinder surface
B. less dose to the cylinder surface
C. more dose to the cylinder surface
D. It depends on the length of the cylinder.
E. There is insufficient information given to determine this.

Answer 13

B. less dose to the cylinder surface

Question 14

The American Brachytherapy Society guidelines for 3D planning for HDR cervical brachytherapy
describe that the dose should be specified in terms of _____.
A. maximum tolerance of the ICRU rectum point
B. maximum tolerance of the ICRU bladder point
C. D90 of the target volume
D. point A
E. point B

Answer 14

C. D90 of the target volume

Question 15

All of the following isotopes are used for permanent prostate implants EXCEPT _____.
A. Pd-103
B. I-125
C. Cs-131
D. Ir-192
E. All of the above are used for permanent prostate implants

Answer 15

D. Ir-192

Question 16

The initial dose rate of a prostate implant is 0.07 Gy/hr using I-125 seeds (T1/2 = 59.5 days). What
total dose will the prostate receive?
A. 100 Gy
B. 108 Gy
C. 125 Gy
D. 144 Gy
E. This cannot be calculated based on the provided information.

Answer 16

D. 144 Gy

Question 17

\_\_\_\_\_ is the unintended dose to a staff member who is 100 cm from the 10-Ci 192Ir source for
10 minutes (192Ir source exposure rate constant is 4.69 R-cm2
 /mCi-h, f Factor = 0.962 cGy/R).
A. 7.5 mGy
B. 15 mGy
C. 30 mGy
D. 50 mGy
E. 75 mGy

Answer 17

A. 7.5 mGy

Question 18

The mean air kerma strength of a batch of Pd-103 (T1/2 = 17 d) seeds is 2.07 U. What is the activity
of the seeds 8 days later?
A. 0.72 U
B. 1.38 U
C. 1.49 U
D. 2.07 U
E. 2.87 U

Answer 18

C. 1.49 U

Question 19

If 90 Pd-103 (T1/2 = 17 d) seeds were intended to be used for a prostate implant, if the implant was
delayed by 8 days, how many additional seeds from the same batch would be needed?
A. 0
B. 35
C. 65
D. 90
E. 120

Answer 19

B. 35

Question 20

In order to generate a uniform dose distribution along an afterloader-based vaginal cylinder, dwell
times for equally spaced dwell positions should be _____.
A. uniform along the cylinder
B. more on both ends, less in the middle
C. less on both ends, more in the middle
D. more on the distal end, less on the proximal end
E. less on the distal end, more on the proximal end

Answer 20

B. more on both ends, less in the middle

Question 21

The advantage of single-catheter, balloon-based HDR techniques over external beam radiotherapy
techniques for partial breast irradiation is _____.
A. one can treat irregularly shaped tumor beds
B. one can sculpt the dose from chest wall or skin
C. high dose gradients and rapid dose fall-off
D. All of the above are true.
E. None of the above is true

Answer 21

C. high dose gradients and rapid dose fall-off

Question 22

Using the U.S. NRC definition, all of the following constitute medical events in a radioactive
isotope treatment with a dose that exceeds 5 rem dose equivalent, EXCEPT _____.
A. treating the wrong patient
B. treating the wrong part of the body and the dose exceeds 50% of what it would have
received if the correct part of the body had been treated
C. administering 25% higher dose than prescribed in one fraction in a multi-fraction
treatment
D. using a wrong radionuclide
E. using a leaking sealed source

Answer 22

C. administering 25% higher dose than prescribed in one fraction in a multi-fraction
treatment

Question 23

An advantage of TG-43 dose calculation is _____.
A. inter-seed attenuation is calculated
B. heterogeneity corrections are applied
C. radiobiological effects due to variation of dose rates within the patient are considered
D. All of the above are true.
E. None of the above is true.

Answer 23

E. None of the above is true

Question 24

A brachytherapy point source delivers 1 Gy/min to a point 1 cm away in a water medium. Given
that the radial dose function of the source g(r) = 0.9 when r = 3 cm, the same source delivers _____
to a point 3 cm away from the source in a water medium.
A. 1.9 Gy/min
B. 1.3 Gy/min
C. 0.9 Gy/min
D. 0.3 Gy/min
E. 0.1 Gy/min

Answer 24

E. 0.1 Gy/min

Question 25

For the same prescribed dose in a permanent implant, selecting a radioisotope with a shorter halflife will necessitate using _____ initial dose rate.
A. a lower
B. a higher
C. the same
D. The relationship between half-life and initial dose rate is isotope dependent.

Answer 25

B. a higher

Question 26

An Ir-192 HDR source is changed between a patient’s second and third brachytherapy fractions.
Which of the following parameters will be different for the third fraction?
A. cumulated activity
B. treatment dose
C. treatment time
D. ratio of time spent in a dwell position to the time spent in the adjacent dwell position
E. All of the above are true.

Answer 26

C. treatment time

Question 27

A proton treatment beam with a spread-out Bragg peak (SOBP), created from combining proton
beams of different energies, has a depth dose profile that differs from any of its component beams
in that its \_\_\_\_.
A. depth of penetration is less
B. surface dose is greater
C. distal fall-off is sharper
D. All of the above are true.
E. None of the above is true

Answer 27

B. surface dose is greater

Question 28

Rank the following in terms of typical skin sparing from BEST TO WORST, given pencil-beam
scanning protons = PBS, uniform scanning protons = US, double scattering protons = DS, and
6 MV x-rays = 6 MVx
A. PBS; US; DS; 6 MVx
B. 6 MVx; DS; US; PBS
C. US; PBS; 6 MVx; DS
D. 6 MVx; PBS; US; DS

Answer 28

D. 6 MVx; PBS; US; DS

Question 29

The uncertainty of the distal range for proton beams arises from _____.
A. SOBP width
B. beam energy
C. CT calibration
D. field size
E. accuracy of the on-board imaging system

Answer 29

C. CT calibration

Question 30

The RBE for protons is highest at the \_\_\_\_\_ of the spread-out Bragg peak (SOBP).
A. entrance region
B. one third point
C. center
D. two thirds point
E. distal edge

Answer 30

E. distal edge

Question 31

The penumbra for proton beams _____ as the depth increases.
A. increases
B. decreases
C. remains the same
D. One is unable to determine this using the information given.

Answer 31

A. increases

Question 32

Failure modes and effects analysis (FMEA) uses occurrence, severity, and detectability indices to
quantify risk of failure modes. These indices are roughly _____.
A. linear
B. logarithmic
C. quadratic
D. sigmoidal
E. None of the above is true.

Answer 32

B. logarithmic

Question 33

In a workplace with an established safety culture, what is expected of an employee who discovers
a radiotherapy near miss, i.e., an issue that if it had been propagated to the patient it might have
caused harm?
A. Report it in the departmental incident learning system.
B. Notify the patient.
C. Notify the institution’s radiation safety officer.
D. Notify the relevant city, state, or national regulatory body.
E. All of the above are true.

Answer 33

A. Report it in the departmental incident learning system.