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preface The RAPHEX Therapy exam 2011 was prepared by members of the Radiological and Medical Physics Society of New York (RAMPS, Inc.), the New York chapter of the American Association of Physicists in Medicine (AAPM). The exam format was changed in 2009 to match the syllabi for teaching Diagnostic Radiology and Radiation Oncology residents published by the AAPM's Subcommittee for Review of Radiation Physics Syllabi for Residents (RRPSR). The numbers of questions for each subject are approximately related to the number of teaching hours allocated to each subject. Exam committee: Cheng-Shie Wuu, Ph.D., Editor Doracy Fontenla, Ph.D. Susan Brownie, M.Sc. Howard Amols, Ph.D. Richard Riley, Ph.D. Eugene Lief, Ph.D. Additional questions contributed by: Clifton Ling, Ph.D. Margie Hunt, M.S. Ellen Yorke, Ph.D. Gig Mageras, Ph.D. Jenghwa Chang, Ph.D. Jussi Sillanpaa, Ph.D. Sean Berry, M.S. Dennis Mah, Ph.D.

Stewart Becker, Ph.D. Lawrence Dauer, Ph.D. Albert Sabbas, Ph.D. Mark Belanich, M.S. Michael Lovelock, Ph.D. Vishruta Dumane, Ph.D. Leonard Rosenstein, Ph.D. Sandra Fontenla, M.S.

Fridon Kulidzhanov, Ph.D. Rostem Bassalow, Ph.D. Laura Happersett, M.S. Marilynn Delamerced, M.S. Yuwei Chi, Ph.D. Pengpeng Zhang, Ph.D. Li Cheng Kuo, M.S. John Humm, Ph.D.

If you are taking RAPHEX under exam conditions, your proctor will give you instructions on how to fill out your examinee and site IDs on the answer sheet.

• You have 3 HOURS to complete the exam. • Non-programmable calculators may be used. • Choose the most complete and appropriate answer to each question.

We urge residents to review the exam with their physics instructors. Any comments or corrections are appreciated and should be sent to: Adel Mustafa, Ph.D. Raphex Chief Editor E-mail: adelmustafa@ gmail.com Copyright© 2011 by RAMPS, Inc., the New York chapter of the AAPM. All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission from the publisher or the copyright holder.

Published in cooperation with RAMPS by:

Medical Physics Publishing 4513 Vernon Boulevard Madison, WI 53705-4964 1-800-442-5778 E-mail: [email protected] Web: www.medicalphysics.org

Printed in the United States of America

therapy questions Tl.

Beta-plus decay has a energy distribution because the energy is shared between the ___ beta-plus particle and the recoil nucleus. A. Discrete B. Continuous beta-plus particle, antineutrino, and recoil nucleus. C. Continuous beta-plus particle, neutrino, and recoil nucleus. beta-plus particle, anti-neutrino, and recoil nucleus. D. Discrete

T2.

Listed below are some elements and their atomic n~mbers (Z). 6°Co decays via beta-minus decay to which of the following isotopes?

Element Fe Co Ni Cu

z 26 27 28 29

A. s9pe B. 59Co C. 60Ni D. 60Cu

TJ.

It is determined that 60 1251 seeds, of a specified activity, are needed for an implant. The case is then postponed for 10 days. How many of these same seeds would you need to implant on the new date? (Half-life of 1251 = 60 days.) A. 60 B. 67 c. 70 D. 77

T4.

A novel isotope with a half-life of 15 days was used for a permanent seed implant. Total dose will be 100 Gy. When the patient returns for further evaluation 30 days post-implant, what dose has he already received? A. 75 Gy B. 78 Gy C. 83 Gy D. 90Gy

TS.

A diagnostic x-ray tube is running at 80 kVp and 10 mAs. The settings are changed to 120 kVp and 5 mAs. What is the approximate change in tube output? A. Does not change B. Decreases by 50% C. Increases by 10% D. Decreases by 10% E. Increases by 50%

Raphex 2011

therapy questions T6.

In the last question, what happens to the image contrast? A. Contrast does not change. B. Contrast increases. C. Contrast decreases. D. Cannot be determined.

T7.

An element contains electrons in the 10, 65, 70, and 72 keV energy levels. Which energy cannot occur in its characteristic x-ray spectrum? A. 5 B. 7 C. 55

D. 60 E. 65

TS.

A conventional x-ray tube is operated at 100 kV. Which of the following is true? A. The minimum x-ray energy is 100 keV. B. The average x-ray energy is 100 keV. C. The maximum x-ray energy is 100 keV. D. Every x-ray has energy of 100 keV.

T9.

The primary collimator in a linear accelerator is located before the: A. Target. B. Flattening filter. C. Bending magnet. D. Accelerator tube.

T I 0.

Which A. B. C. D. E.

T I I.

In which of the following is the microwave power absorbed at the end of the waveguide? A. Traveling waveguide B. Standing waveguide C. Superficial therapy unit D. Proton cyclotron

of the following is not part of a diagnostic x-ray machine? Waveguide Transformer Target Rectifier Filament

1

2

Raphex 2011

therapy questions T 12.

A linear accelerator used for radiation therapy with photons accelerates: A. Electrons. B. Photons. C. Electrons and x-rays. D. Neutrons. E. Protons.

T 13.

A TomoTherapy® unit incorporates which modalities into a single machine? A. Kilovoltage CT, Megavoltage linear accelerator B. PET scanner, Megavoltage linear accelerator C. MRI scanner, Megavoltage linear accelerator D. Megavoltage CT, Megavoltage linear accelerator E. Megavoltage CT, Proton accelerator

T 14.

In CT treatment planning using heterogeneity corrections, planners may sometimes contour structures and assign them the CT numbers of air or water. This would be appropriate for which of the following cases? A. Streaking artifacts in tissues near a metal prosthesis B. Wire markers outlining the scar of an electron boost C. Contrast medium in the GI tract D. All of the above.

TIS.

The photon interaction most responsible for the prominence of bony anatomy on kV images is: A. The Compton effect. B. Pair production. c~ The photoelectric effect. D. Electron capture. E. Coherent scatter.

T 16.

The probability of the photoelectric effect per unit mass is proportional to which power of the nuclear charge Z? A. 0 B. 1 c. 2

D. 3 E. None of the above.

Tl7.

A 5 ke V photon undergoing coherent or classical scatter would be most likely to lose of its energy in the process. A. 0 B. 10 c. 50

%

D. 90 E. 100

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therapy questions TIS.

Compton-scattered electrons can be emitted at incident photon. A. Any angle B. 0°-90° c. 30°-120° D. 90°-180°

T 19.

In Compton interactions, which of the following is true? A. The photon changes direction but does not lose energy. B. The electron may acquire any energy from zero up to the energy of the incident photon. C. The maximum energy is imparted to the electron when the photon is scattered at 180°. D. A neutrino is emitted. E. The probability of a Compton interaction increases continuously as photon energy increases.

T20.

A photoelectric interaction occurs between an 8 ke V photon and a K shell electron. A 3 ke V photoelectron is emitted. The binding energy of the K shell is ke V. A. 0 B. 34.0 c. 5 D. 8.0 E. 11.0

Tll.

Conceming pair production, which of the following is true? A. The threshold energy for pair production is 0.51 MeV. B. An electron and a positron are produced. C. The energy of the incident photon is equal to the sum of the kinetic energies of the pair of particles. D. Annihilation produces 1.02 MeV photons. E. A pair of electrons is produced.

T22.

Which A. B. C. D.

Tll.

The fractional number of photons removed from a beam per centimeter of absorber is called the: A. Linear attenuation coefficient. B. Mass absorption coefficient. C. Scatter coefficient. D. Mean attenuation length.

4

with respect to the direction of the

of the following statements regarding photoelectric interactions is false? They are mainly responsible for differential attenuation in diagnostic radiographs. The incident photon is absorbed. The probability increases rapidly with increasing energy. Bound electrons are involved.

Raphex 2011

therapy questions T24.

Which A. B. C. D. E.

of the following will most reduce the x-ray beam penumbra on a linear accelerator? Decreasing the distance from target to secondary collimators Decreasing the dose rate Increasing the depth in the patient Using an MLC in addition to x-y jaws Using a focused cerrobend block in addition to x-y jaws

TlS.

As the A. B. C. D. E.

x-ray energy increases from 1 MV to 20 MY, the half-value layer, in lead: Increases. Decreases. First decreases, then increases. First increases, then decreases. Stays nearly constant.

T26.

When measuring the HVL of an x-ray beam, a narrow beam must be used because: A. The beam must be smaller than the detector.. B. A broad beam could introduce scattered x-rays, giving a false reading. C. The average beam energy would be greater with a broad beam. D. All of the above are true.

T27.

In a 16 A. B. C. D.

T28.

The linear attenuation coefficient of a beam is 0.1 cm- 1• The HVL is: A. 14.4 em. B. 6.93 em. C. 1.44 em. D. 0.693 em. E. 0.693 mm.

T29.

Neutrons have a higher Quality Factor than electrons because: A. They transfer energy to protons, which have a high LET. B. They slow down in tissue, and deposit most of their energy at the end of their track. C. They have a large mass and charge. D. They are directly ionizing.

Raphex 2011

MV photon beam at 1 em depth: The kerma is greater than the absorbed dose. The absorbed dose is greater than the kerma. The percent depth dose equals 100%. Electronic equilibrium exists.

5

therapy questions T30.

In diagnostic x-ray systems, filters are used to "harden" the beam. This process is mainly due to: A. Coherent scattering. B. Photoelectric effect. C. Compton effect. D. Pair production.

Tll .

A photon counter detects 10,000 counts. What is the % uncertainty for the number of counts detected? A. 0.1% B. 0.3% c. 1% D. 3% E. 10%

T32.

What happens if the A. The reading B. The reading C. The reading D. The reading

T33.

The AAPM recommends the use of a A. Thimble ionization chamber B. Parallel-plate ionization chamber C. Diode D. Any of the above.

T34.

The protocol currently recommended by the AAPM for calibrating megavoltage therapy units is: A. SCRAD. B. TG-21. C. ICRU Report 21. D. TG-51. E. None of the above.

T35.

Ionization chambers used for machine calibration require temperature and pressure corrections to account for: • A. Variations in the mass of air in the collection volume. B. The expansion of the air at high pressure. C. The contraction of the air at high temperature. D. Variations in the probability of ionization at different temperatures. E. None of the above.

6

bias voltage on an ionization chamber is too low? is too high. is too low. will be zero. will be correct if proper temperature pressure corrections are applied. to calibrate a 6 MeV electron beam.

Raphex 2011

therapy questions T36.

The output of a linear accelerator's photon beam is calibrated to be 1.0 cGy/MU. This calibration point is always at: A. Depth dmruo 100 em SSD, 10x10 em field size. B. Depth 10 em, 100 em SSD, 10x10 em field size. C. Depth dmax• 100 em SAD, 10x10 em field size. D. Depth 10 em, 100 em SAD, 10x10 em field size. E. A depth, distance, and field size specified by the physicist, consistent with data used for treatment planning.

Tl 7.

Regarding the AAPM's current calibration protocol, all of the following are true, except: A. The ion chamber must be calibrated at an accredited lab, in water, and in a Co-60 beam. B. The chamber and electrometer must be calibrated every 2 years. C. Photon beam quality is defined by the percent depth dose at 10 em depth in water. D. Only Farmer-type chambers can be used. E. The protocol can be used for photons and electrons.

T38.

For a superficial x-ray unit, if there is no measured data, the two factors necessary to select the correct POD table from published data are: A. Filtration and kVp. B. kVp and SSD. C. HVL and SSD. D. Filtration and SSD.

T39.

In a treatment planning computer, what is the most accurate method of calculating the dose distribution in a patient (especially at interfaces)? A. Ratio of TARs (RTAR) B. Equivalent TAR (ETAR) C. Convolution-superposition D. Monte Carlo

T40.

Cumulative dose-volume histograms can show all of the following, except: A. The dose homogeneity over the PTV. B. The maximum dose in an organ. C. The percent of a contoured volume receiving a specific dose. D. The location of the maximum tissue dose. E. The minimum dose in an organ.

T 41.

Regarding tissue inhomogeneities, changes in secondary electron fluence strongly affect the dose: A. Up to a few centimeters downstream of the inhomogeneity. B. Upstream of the inhomogeneity. C. Within the inhomogeneity. D. Near the boundaries of the inhomogeneity. E. C and D above.

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therapy questions T42.

The primary advantage of treating breast cancer patients in the prone position is to: A. Make the patient more comfortable. B. Create a more reproducible patient setup. C. Treat less lung tissue. D. Create a more uniform target. E. Increase the dose to the skin.

T 43.

Regarding dose-volume histograms, which of the following is true? A. The D 95 (dose received by 95% of the PTV) is an indicator of the hot spot within the structure. B. The D 95 for the PTV should ideally be as low as possible. C. D05 for the PTV should ideally be as high as possible. D. D 05 and D 95 in the PTV should be as close as possible. E. For an organ at risk the D05 should be as high as possible.

T44-T4S. Use the table below for the next two questions. Data Tables for 6 MV Photons (PPD are for 100 em SSD) Field Size (em)

5x5

10 X 10

15 X 15

20 X 20

25 X 25

87.1 75.0 67.6 51.6 39.2

87.6 76.3 69.2 53.7 41.5

87.9 77.3 70.3 55.4 43.4

88.2 77.9 71.1 56.4 44.5

Depth (em)

PDD

5 8 10 15 20

TMR

5 8 10 15 20

85.6 72.0 64.2 47.7 36.7

sc sp

0.912 0.809 0.745 0.602 0.487

0.928 0.842 0.784 0.647 0.530

0.934 0.857 0.804 0.675 0.560

0.937 0.869 0.818 0.697 0.586

0.941 0.877 0.828 0.713 0.605

0.970 0.975

1.000 1.000

1.015 1.017

1.024 1.029

1.027 1.031

= 1.0 at dmax (1.5 em), 100 em SAD, Field Size: 10x10 em Output (cGy/MU) = 0.971 at dmax (1.5 em), 100 em SSD, Field Size: 10x10 em Output (cGy/MU)

T44.

8

.

A patient is treated with isocentric AP/PA fields, 16x14 em, 6 MV x-rays. The prescription is 150 cGy/field to the midplane depth of 8 em. The treatment field is MU. shaped to 10xl0 em with MLC. The MU setting per field is A. 163 B. 176 c. 200 D. 222 E. 358

Raphex 2011

therapy questions T45 .

A patient is treated to the thoracic spine with a single posterior field, 100 em SSD setup, 15x10 em, 6 MV x-rays. The prescription is 300 cGy/field to a depth of 5 em. There is no blocking. The MU setting per field is MU. A. 305 B. 317 c. 339 D. 349 E. 360

T 46.

Generally 6 MV photons are suitable for delivering uniform dose distributions to breast with hot spots less than 110% when the maximum separation is less than approximately: A 15 em. B. 25 em. C. 35 em. D. The separation is irrelevant.

T 4 7.

Which energy is more suitable for treating a lung lesion, 6 MV or 18 MV? A. · 18 MV, since the separation is large in the thorax B. 6 MV, since the build-up region is much larger for the 18 MV beam C. 6 MV, since the total MUs will be lower D. 18 MV, because of fewer MU E. 18 MV, because of smaller penumbra

T48.

Two adjacent 20x20 em fields (100 em SSD) are to be matched at a depth of 5 em. What is the gap at the skin? A. 0.5 B. 1 c. 2 D. 4

T49.

A patient is treated with two adjacent fields. One has a collimator setting of 10x10 em and 120 em SSD. The second field has 20x20 em collimator setting and 100 em SSD. What gap is required at the skin for these fields to intersect at 5 em depth? A. 0.65 B. 0.70 c. 0.75

--

D. 1.0

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therapy questions TSO.

An isocentric 10x10 em 6 MV photon beam passes through 4 em of chest wall and 7 em of lung. If calculations were done without heterogeneity corrections, the isocenter would receive: A. An overdose of about 35%. B. An overdose of about 18%. C. An overdose of about 5%. D. An underdose of about 7%. E. An underdose of about 15%.

TS I.

When a patient is treated with a single megavoltage beam, the surface dose, relative to the maximum dose: A. Increases as the energy increases. B. Is on the order of 10% to 40%. C. Does not depend on field size. D. Decreases when a block tray is placed in the beam.

TSl.

A superficial x-ray unit has an SSD of 20 em to the end of the applicator. If an additional air gap of 2 em is left, and no correction is made, this would cause the dose at drnax to be: A. 22% high. B. 9% high. C. 9% low. D. 17% low. E. 25% low.

TSJ.

The definition of Fractional Depth Dose (i.e., PDD/100) is: A. (dose rate at drnax)/(dose rate at depth) measured at the same SSD. B. (dose rate at depth)/(dose rate at dmax) measured at the same SSD. C. (dose rate for the field size at depth)/( dose rate for a 10x10 em field at depth). D. (dose rate at depth, measured at SSD)/(dose rate at drnax• measured at SAD). \

TS4.

The primary beam of a linac is set to 40x40 em at the isocenter (100 em from the source). This projects to em at the wall, which is 4 m from the isocenter. A. 80 B. 120 c. 160 D. 200 E. 240

TSS.

A field of collimator setting 8x30 em has an equivalent square of A. 10.5 B. 12.6 c. 19.0 D. 22.4

10

em.

Raphex 2011

therapy questions TS6.

A patient's spine is treated at 130 em SSD, in order to obtain a longer field. Compared with the same collimator setting treated at 100 em SSD, all of the following are true, except: A. The PDD at 6 em depth will be slightly greater. B. The output (cGy/MU) at dmax will be [(100+dmax)/(130+dmax)])2 of that at 100 em SSD. C. The exit dose will be greater. D. The surface dose will be slightly greater.

TS7.

A plan is calculated to deliver 200 cOy/fraction to the isocenter, and normalized to 100% at this point. The hot spot is 105%. The physician chooses. to treat to the 95% isodose. If the plan is renormalized to reflect this change, all of the following are true, except: A. The MU for each field will be increased by 5%. B. The isodose at the isocenter is now 105%. C. The hot spots in the plan are now 110%. D. The dose to an adjacent OAR will be reduced by 5%.

TS8.

A patient's abdomen is treated with AP/PA isocentric 6 MV photons. During treatment the patient's AP separation increases from 24 to 28 em. The dose delivered, if uncorrected, will be: A. 15% low. B. 7% low. C. 3% low. D. 7% high. E. 15% high.

TS9.

Which of the following changes would have the greatest effect on the MU calculation for a 6 MV photon beam to deliver the same dose? The initial calculation is for 6x6 em, 100 em SAD, d = 10 em. A. Changing the collimator setting from 6x6 em to 8x8 em. B. Changing the depth from 10 em to 11 em. C. Changing from 100 SAD to 100 em SSD. D. Adding a 1 em plastic blocking tray. E. Adding 1 em of bolus.

T60.

In a 3-field pelvis plan with a PA and opposed lateral fields, all of the following are true,

except: A. The wedges on the lateral fields compensate for the dose gradient of the PA field across the PTV. B. 45- and 60-degree wedges can both give homogeneous dose distributions over the PTV. C. The thick ends of the wedges will be towards the anterior. D. Weighting (relative dose at the isocenter) for a uniform dose over the PTV will depend on the wedge angle used.

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therapy questions T61.

Dynamic wedges may have all of the following limitations, except: A. There is a minimum field size in the wedge direction. B. There is a minimum collimator setting at the thin end of the wedge. C. There is a minimum MU. D. There is a minimum field size in the non-wedge direction. E. The wedge orientation may not be compatible with the MLC direction for some blocked fields .

T62.

The tangential fields in the diagram are angled so that their posterior borders are aligned. LAO gantry angle= 60°. Field width= 18 em (symmetrical) at 100 em SAD. (Gantry angles are defined as: 0° = anterior; 90° =patient left.) RPO Gantry angle = _ __ A. 240° B. 240° + 10° c. 240° + 1S 0 D. 240°E. 240°-10°

+so so

Angle tan- 1

e

0 0

s 0.09

10 0.18

1S 0.27

20 0.36

T63.

It has been recommended that the dose to a pacemaker be kept below 2.0 Gy. In a lung treatment of 40 Gy with 6 MV photons, the fields should be no closer than to the pacemaker. A. O.S,cm B. 2cm C. 7 em D. 10 em

T64.

Typically, a linac capable of producing x-rays and electrons has a target, flattening filter(s), and scattering foil(s). Which of the following is true regarding these three items? A. All three items are used in X-ray mode. \-" B. Only a target and scattering foil are used in X-ray mode. C. Only a scattering foil is used in electron mode. D. None of them are used in electron mode.

12

Raphex 2011

therapy questions T65.

Electrons appear to emanate from a virtual source. The virtual source, relative to the photon source, 1s: A. Closer to the patient. B. Further from the patient. C. In the same place. D. Both A and B can be true depending on the electron energy.

T66.

A superficial tumor is to be treated to a depth of 1 em while sparing a critical structure at a depth of 2 em, using electrons with a 9-cm circular field. The most suitable technique would be: A. 6 MeV electrons without bolus. B. 6 MeV electrons with 0.5 em bolus. C. 6 MeV electrons with 1.0 em bolus. D. 9 MeV electrons with 0.5 em bolus. E. 9 MeV electrons with 1.0 em bolus.

T67.

For a lOx lO em electron cone, using an energy of 12 MeV, the electron field size can be blocked down to without significantly affecting the central axis depth dose. A. 9x9 em B. 8x8 em C. 6x6 em D. 3x3 em

T68.

A lOxlO em 16 MeV electron beam has 90% depth dose at about A. 1.5 B. 3 c. 5 D. 8

T69.

The dose measured beyond the practical range of a therapy electron beam is due to: A. Very low-energy electrons. B. The highest energy electrons in the spectrum. C. Characteristic x-rays generated in tissue. D. Bremsstrahlung.

T70.

In soft A. B. C. D. E.

Raphex 2011

em.

tissue, a beam of 9 MeV electrons loses most of its energy by: Bremsstrahlung radiation. Ionization. Compton interactions. Collisions with nuclei. Pair production.

13

therapy questions T71.

All of the following are potential advantages of electrons over superficial x-rays, except: A. No increased dose to bone. B. Small amount of skin sparing. C. Greater sparing of underlying tissue. D. Easy to shape field with thin sheet of lead. E. Greater output means faster treatment.

T72.

According to the AAPM, and regulatory agencies, the annual calibration of a linac output %. should have an accuracy of better than A. 0.5 B. 1 C. 1.5 D. 2 E. 5

T73.

On an accelerator equipped with a gantry-mounted kV x-ray tube and imager, which of the following tests should be performed daily? (According to the AAPM) A. Positioning of the tube and detector, relative to the accelerator isocenter B. Low contrast resolution C. Entrance exposure D. HVL E. A and D only

T74.

Accelerators are calibrated as dose to water or muscle. A clinic uses calibration to water but participates in a multi-institutional protocol specifying dose to muscle. A plan is done on a participating patient, and one of the beams is calculated as 100 MU, still assuming dose to MU. water. To comply with the protocol, the beam-an-time needs to be changed to A. 98 B. 99 C. 101 D. 102

T75.

What is the array size, i.e., number of pixels, of a single slice of a standard CT scan? A. 256x256 B. 512x512 C. 800x600 D. 1024x768

14

Raphex 2011

therapy questions T76.

At a therapy workstation in aCT control room, a radiation oncologist outlines the tumor, organs at risk (OARs), establishes an isocenter, and chooses some preliminary beams. The CT operator pushes the patient data to a modem treatment planning system (TPS) using DICOM instead of DICOM-RT. What information is not sent to the TPS? A. Patient identifying information B. CT numbers (Hounsfield units) C. Field of view and slice thickness D. Tumor, OARs, isocenter, and beams

T77.

According to the National Council on Radiation Protection and Measurements (NCRP), the recommended shielding design goal (P) in dose equivalent is in controlled areas, and ___ in uncontrolled areas. A. 500 mSv year- 1 100 mSv week- 1 1 B. 0.02 mSv week0.1 mSv week- 1 1 C. 0.1 mSv week0.02 mSv week- 1 1 D. 1 mSv year1 mSv week- 1

T78.

When designing shielding for a 6 MV linear accelerator, the tenth-value layer (TVL) for concrete (density 2.35g cm-3) is about 33 em. The TVL in lead (density 11.35g cm-3) would be about em. A. 3.3 B. 5.7 c. 33 D. 57

T79.

Important safety features of an 192Ir High Dose Rate Brachytherapy treatment room include all of the following, except: A. Audible and visual contact with patient. B. Calibrated survey meter. C. Posted emergency procedures. D. Lead aprons for patients and staff. E. Warning signs for high radiation area and radioactive material.

T80.

The U.S. Nuclear Regulatory Commission considers a reportable "medical event" to be based on both dose thresholds and percent differences from prescribed doses. Which of the following would be considered a medical event? ·A. 0.05 Sv overdose with an 11% difference in total dose. B. 0.55 Sv overdose to an organ or tissue with 22% difference in total dose. C. 0.55 Sv ovel;.dose to an organ or tissue, with a single fraction difference of 22% and a total dose difference of 2%. D. 0.05 Sv overdose with a 22% difference in total dose.

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therapy questions T81.

The material in a treatment room door commonly used for neutron shielding is: A. Paraffin wax. B. Lead. C. Concrete. D. Borated polyethylene. E. Anodized polystyrene.

T82.

Using a smaller CT slice thickness during simulation is useful in image-guided r~diation therapy (IGRT) because of: A. Smaller CT dose to the patient. B. Less work is required for normal tissue and target contouring. C. Faster CT reconstruction. D Improved DRR image quality. E. Less computer storage space required.

T83.

In lung patient simulation, a slow CT scan is sometimes performed when 4DCT is not available. Which of the following is not true regarding slow CT scanning? A. The scan needs to cover multiple respiration phases. B. The image resolution will be better. C. The purpose is to capture extent of tumor motion. D. Patient dose will be more than for a normal CT scan. E. The CT can be used for target delineation.

T84.

Advantages of using gating for lung treatment include all of the following, except: A. Reduced overall treatment time. B. Ability to use smaller margins when drawing the PTV. C. Patient does not have to hold his or her breath. D. Ability to spare more normal tissue.

T85.

Which of.the following isotopes is most commonly used in PET imaging? A

18p

B

I9p

D. E.

1241

c.

T86.

16

Wl1ich A. B. C. D.

13 II

uc of the following statements is not true of magnetic resonance (MR) imaging? Typical magnetic field strengths of MR scanners are between 1.5-3.0 tesla. MR images can be distorted by variations in magnetic fields. MR image pixel intensities are proportional to tissue electron density. Typical MR images contain a matrix of 256x256 or 512x512 pixels.

Raphex 2011

therapy questions T87.

In amorphous silicon electronic portal imaging devices (EPIDs), the main purpose of the combination metal plate/phosphor screen is to: A. Convert incident x-rays into visible light. B. Filter out contaminant electrons exiting the patient and support couch. C. Prevent backscatter of x-rays into the EPID. D. Attenuate Compton-scattered x-rays, which improves image quality.

T88.

For images obtained using an EPID, scatter photons increase all of the following, except: A. Signal. B. Noise. C. SNR (signal-to-noise ratio). D. CNR (contrast-to-noise ratio).

T89.

A patient is treated with respiratory gating with a duty cycle of 25%. The treatment machine is running at 400 MU/min. Approximately how long does it take to deliver a 100 MU field? A. 20 seconds B. 40 seconds C. 60 seconds D. 80 seconds E. 120 seconds

T90.

Which of the following is true? A cone beam CT: A. Is generally acquired in a single rotation of the x-ray tube. B. Has worse resolution than regular diagnostic multiple-slice CT in the cephalocaudad direction. C. Requires roughly three times as much dose as regular diagnostic multislice CT. D. Is ideal for scanning long tre~tment volumes.

T91.

Regarding 2D kV planar imaging and 3D kV CBCT used for IGRT, which of the following is true? Both 2D and 3D.kV: A. Require higher resolution image detector plates than MV imaging. B. Are excellent for determining rotational setup errors. C. Are valuable when used for patients with small implanted metallic fiducials. D. Allow visualization of soft-tissue anatomy.

T92.

A half-fan CBCT (i.e., imager is shifted laterally) is taken instead of a full-fan CBCT in order to? A. Avoid collision. B. Increase the reconstruction volume in the axial plane. C. Increase the reconstruction volume in the sup-inf direction. D. Increase image quality, keeping the reconstruction volume the same.

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therapy questions T93.

For stereotactic body radiotherapy (SBRT), which of the following systems is capable of real-time imaging and monitoring intrafractional motion of bony targets in three dimensions? A. Gantry-mounted kV source and imaging system B. Dual room (ceiling- or floor-) mounted kV imaging systems C. An MV imaging system D. A tomographic imaging system E. An in-room CT-on-Rails system

T94.

What imaging modality does CyberKnife® use for target localization? A. Cone beam CT B. Orthogonal x-ray C. Tomosynthesis D. Ultrasound

T9S. ·

What is the primary imaging modality for Gamma Knife® planning? A. CT B. MRI C. PET D. Ultrasound

T96.

Comparing kV cone beam, CT-on-Rails, and MV cone beam, which has the best image quality? A. MV cone beam B. CT-on-Rails C. kV cone beam D. All techniques yield approximately comparable image quality.

T97.

Which statement about the PTV is false? A. The PTV is larger than and includes the GTV. B. The PTV is larger than and includes the CTV. C. The PTV must be obtained from the CTV by enlarging the CTV with uniform margins in all directions. D. The PTV should account for setup uncertainties. E. A treatment plan can have two unconnected PTV s.

T98.

One reason that MRI images are rarely used alone (i.e., without accompanying CT images) for planning conformal radiation therapy treatments is that: A. It is more difficult to delineate the GTV on MRI images. B. Transverse MRI images cannot be obtained. C. MRI images may be subject to geometric distortion. D. MRI images cannot be obtained in the treatment position. E. MRI images cannot be transferred to treatment-planning computers.

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therapy questions T99.

A prostate patient was simulated with implanted RF beacons. During patient setup, the software cannot fmd or track the beacons. This could be due to all of the following reasons, except: A. Urologist accidentally implanted gold markers instead of RF beacons. B. Patient has a hip replacement. C. Beacon coordinates entered incorrectly into the software. D. Patient is a heavy breather.

TIOO.

Two orthogonal MV localization images (one AP plus one LAT) are taken daily for 40 fractions, to image fiducials in a patient's prostate. The approximate additional dose to the isocenter from these images over the course of treatment is cGy.' A. Negligible B. 10 c. 75 D. 130 E. 500

TIOI.

As compared to radiographs taken on a conventional simulator, digitally reconstructed radiographs (DRRs) from aCT simulation typically have which of the following? A. Comparable spatial resolution in all directions B. Better resolution in all directions C. Better resolution only in the cranial-caudal direction D. None of the above.

TIOl.

Image-guided radiotherapy (IGRT) can use a variety of imaging modalities at the time of treatment, including 2D images using kV and MV sources. Compared to MV images, kV images have all of the following features, except: A. Easier visualization of bones. B. More similar to DRRs generated with planning CTs. C. Deliver a higher midplane dose. D. Require careful alignment to match the isocenter of the treatment (MV) beam.

TIOJ.

Which of the following techniques can benefit from independent modulation of gantry speed, MLC speed, and dose rate during treatment? A. IMRT B. IMAT C. Dynamic conformal arc D. Electron arc therapy

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therapy questions TI04.

A patient is undergoing IMRT treatment. The prescription dose is changed from 180 to 200 cGy per fraction. The overall prescribed dose for the course does not change. The MU for each field: A. Will change because an entirely new plan is required. B. Will increase by 200/180. C. Will not change. The dose can be increased by increasing the dose rate on the accelerator. D. Must be determined through direct measurement on the accelerator.

TIOS.

Which of the following statements is not true regarding intensity-modulated arc therapy (IMAT) vs. intensity-modulated radiation therapy (IMRT)? A. Intrafractional motion should be reduced with IMAT, because the delivery time is shorter than for IMRT B. IMAT requires more stringent linac QA tests because sychronization of gantry, MLC motion, and dose rate modulation must be accurately maintained. C. A single arc IMAT always yields better dose distributions than IMRT. D. Pretreatment QA must be performed for both IMRT and IMAT.

TI06.

As the complexity of fluence modulation increases in an IMRT plan, which of the following is true? A. The monitor units increase. B. The average leaf gap decreases in sliding-window IMRT. C. Leakage dose increases. D. All of the above.

TI07.

For IMRT treatment planning, which parameter is not set by the planner? A. Gantry angles · B. Beam weights C. Prescription D. Energy

TI08.

Wh ich of the following systems is not suitable for dosimetric measurement of a 1 em diameter SRS/SBRT field? A. 0.6,cc Farmer chamber B. Thermoluminescent dosimeter C. Silver-halide-emulsion film D. Diodes

TI09.

For Gamma Knife® treatments, the prescription dose is commonly prescribed to which of the following isodose curves? A. 100% B. 90% c. 85% D. 50% E. 45%

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therapy questions TIIO.

A definition for the conformity index (CI) is (volume covered by prescription isodose line)/(volume of the target). A CI = 1 implies that: A. The target will be perfectly covered by the prescribed dose (no over- or under-irradiation). B. Part of the target will receive less than the prescribed dose. C. Some of the normal tissue will also receive the prescribed dose. D. The target may be completely missed by the prescribed dose. E. Any of the above.

T I I 1-T I 13.

Use the following diagrams for the next three questions. The lead SRS cone shown below is attached to an aluminum mounting plate. The bottom of the cone is 70 em from the target. The outer diameter of the cone projects to 10 em at isocenter.

2cm~ ,,f'' • • ~i',:'l

Ph - Side view

r

lim

?em

Cross section at end of cone, 70 em from target

Tlll.

What is the largest square jaw setting, in em, that can be used for SRS treatment? A. 10x10 B. 4x4 C. 8x8 D. 7x7

T112.

In the above figure, what are the main reasons the cone is 10 em thick? A. To adequately block the beam outside the aperture and reduce the penumbra

B. To minimize the scattering and increase beam penetration C. To align with the setup laser at two locations

D. Mechanical integrity

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therapy questions T113.

Once the cone system in the figure on page 21 is attached to the linac, the light field can only be observed through the cone aperture. Which of the following should be performed? A. Winston-Lutz test using film large enough to detect radiation outside the area of the lead cone B. Verifying the appropriate jaw size has been set C. Disabling jaw motion D. All of the above.

T114.

For a radiosurgical treatment of an AVM, the conformality index corresponding to the 14 Gy prescription dose, as calculated by the planning system, is 1.3. The DVH for the target indicates that V(l4 Gy) is 95%. The AVM volume is measured to be 23.5 cc. The volume of brain-tissue receiving at least 14 Gy is cc. A. 30.6 B. 29.0 c. 22.3 D. 14.0

TIIS.

Compared to conventional fractionated plans, SBRT plans typically have a target dose and a dose gradient outside the PTV. A. Higher steeper B. Higher less steep C. Lower steeper D. Lower less steep

Tll6.

Prior to the second fraction of a vaginal cylinder case, the HDR source was changed to a higher activity. When delivering the second fraction: A. Dose increases, time increases. B. Dose stays the s_ame, time increases. C. Dose decreases, time decreases. D. Dose stays the same, time decreases.

Tll7.

The adv antage of using multi-lumen balloons to perform Partial Breast Irradiation with HDR is the ability to: A. Treat a larger volurrie. B. Better control the dose distribution. C. Treat in a prone position vs. supine. D. Decrease dose to the skin when necessary. E. Answers Band D.

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maximum

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therapy questions Tll8.

A MammoSite HDR treatment, with a single dwell position at the center of the spherical balloon, is planned from orthogonal x-rays. By mistake, a magnification factor of 1.4 is used instead of the correct value (1.29). The delivered dose will then be: A. 9% too high. B. 8% too low. C. 15% too low. , D. Not affected by this mistake.

Tll9.

For HDR treatment using a titanium tandem and ovoid applicator, it is suggested that planning be done using MR scans to better delineate the tumor. Which of the following is correct? A. The plan can be done from an MRI scan, using the same applicator. · B. The plan can be done from an MRI scan, but a non-metallic applicator must be used. C. The same applicator can be used, but an additional CT scan should be acquired to calculate inhomogeneity corrections. D. A non-metallic applicator must be used, and in addition to the MRI, a CT scan should also be acquired to calculate the inhomogeneity corrections.

TllO.

For a vaginal cylinder HDR plan entered manually at the console, a step size of 1.0 em is entered instead of the planned 0.5 em. How does this affect the dose? A. The shape of the dose distribution is not affected, but the whole distribution is moved to a different location. B. The location of the dose distribution is not affected, but it no longer has the optimized shape. C. The shape, dose, and location of the distribution are affected. D. The shape and location of the dose distribution are not affected, but the absolute dose changes.

Till.

An HDR vaginal cylinder plan is optimized to deliver a uniform dose 0.5 em beyond the cylinder surface. Which of the following is true regarding the dose distribution at different distances? A. At shorter distances, the ends will be hotter than the center, whereas at longer distances, the center will be hotter. B. At shorter distances, the ends will be colder than the center, whereas at longer distances, the center will be colder. C. The dose will be almost uniform at distances up to 5 em from the surface.

Till.

The energy of the most prevalent gamma ray emitted by A. 21 B. 28

c.

131

! is

keV.

110

D. 364 E. 662

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therapy questions Till.

All of the following are true of 125 I, except: A. Strands of seeds can be used for permanent implants. B. It is commonly used for prostate implants . . C. It can be created by neutron activation. D. Mean energy is about 350 keV. E. The useful radiation is mostly characteristic x-rays, not gamma rays.

Tl24.

A permanent 125 I seed implant has an initial dose rate of 0.1 Gy/h. The total dose delivered by this implant is Gy. · A. 207 B. 156 c. 100 D. 10 E. 8.6

Tl25.

For the same dose rate, the required total activity of 125I will be 192 Ir were to be used. A. Greater than B. Less than C. The same as D. Cannot tell from the information given

Tl26.

An 192Ir HDR unit has an activity of 8.6 Cion May 2. The treatment time for a vaginal cylinder is 300 seconds. If the treatment time for a similar treatment is not to exceed 10 minutes, the source must be changed on: A. July 15. B. June 23 . C. July 1. D. August 5.

Tl27.

In brachytherapy, advantages of HDR compared to conventional LDR include all of the following, except: A. Reduced need for hospital stay. B. Reduced radiation exposure to staff, under normal operating conditions. C. Simplifies source inventory and calibration, as only one source is used. D. Dose distribution can be optimized. E. Reduced risk of norma1 tissue complications.

Tl28.

The advantage of using larger diameter ovoids in a Fletcher-Suit applicator is: A. They are easier to see on a localization radiograph. B. They result in a higher mucosal dose rate. C. They result in a lower mucosal dose rate and better depth dose distribution. D. They result in a lower dose to the bladder and rectum.

24

that needed if

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therapy questions Tl29.

In the treatment of metastatic thyroid cancer, some institutions attempt to administer the maximum tolerated activity of 131 1 consistent with dose limiting toxicity. What is the usual dose-limiting organ when treating thyroid cancer with orally administered radioiodine? A. Salivary gland B. G.I. tract C. Lung D. Retina E. Bone marrow

TllO.

What thic~f lead is required to reduce the exposure from a 99mTc source producing 0.64 mSv/Q. at 1 meter to an acceptable level in an unrestricted area? (The HVL in lead is 0.027 em.) A. 0.0135 em B. 0.135 em C. 1.35 em D. 13.5 em E. 135 em

Till.

What is the approximate whole body radiation dose to a patient who undergoes a PET scan using 10 mCi FDG? A. 0.02 cGy B. 0.2 cGy C. 2 cGy D. 20 cGy E. 200 cGy

Till.

Hyperthermia is usually performed in the following temperature ranges: A. 34-39 °C for 1-2 hours. B. 39-40 °C for 1-2 hours. C. 41-45 °C for 30-60 minutes. D. 45-50 oc for 30-60 minutes.

Till.

The1mal enhancement ratio (TER) is defined as: A. RT dose without heat/RT dose for equivalent effect with heat. B. RT dose equivalent with heat/RT dose without heat. C. Temperature before RT!Temperature after RT. D. Specific Absorption Rate (SAR) with RT/SAR without RT.

Tll4.

Proton A. B. C. D.

Raphex 2011

beams have which of the following clinical advantages? Adjustable RBE Less sensitive to positioning errors No exit dose Easily generated from radioactive materials

25

therapy questions TIJS.

26

All of the following techniques will increase the neutron contamination in a proton therapy machine, except: A. Moving the range shifter or energy mpdulator closer to the patient. B. Using a scanning beam instead of a scat-tered beam. C. Placing the field-shaping collimator closer to the patient. D .. Increasing the primary proton energy.

Raphex 2011