raphex 2012.pdf
TRANSCRIPT
therapy -xamination
preface
The RAPHEX Therapy exam 2012 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. Susan Brownie, M.Sc. Richard Riley, Ph.D. Eugene Lief, Ph.D. Howard I. Amols, Ph.D., Senior Editor
Additional questions contributed by: Margie Hunt, M.S. Ellen Yorke, Ph.D. Gig Mageras, Ph.D. Jenghwa Chang, Ph.D. Jussi Sillanpaa, Ph.D.
Lawrence Dauer, Ph.D. Michael Lovelock, Ph.D. Rostem Bassalow, Ph.D. Marilynn Delamerced, M.S. Sean Berry, M.S.
Dennis Mah, Ph.D. Gil'ad Cohen, M.S. Maria Chan, 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:
Howard I. Amols, Ph.D. Senior Editor E-mail: [email protected]
Copyright© 2012 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
•• ••
~. rilpp . : • •• •
E-mail: [email protected] Web: www.medicalphysics.org
Printed in the United States of America
therapy questions
T I. Which of the following brachytherapy isotopes cannot be easily produced in a nuclear reactor? A. 9osr
B. 103pd c. 137Cs D. I92Jr
T2. An element has only one stable isotope of Z protons and N neutrons (2<80). For the isotope with Z protons and N+ 1 neutrons, what is the most likely mode of decay?
A. Isomeric transition B. Fission C. ~+ D. 13-
Tl. An isotope, 228 A, goes through a chain of a and ~-decays. Which of the following is NOT a possible daughter in this chain? (Note: Letters used to denote isotopes in this question are not chemical symbols.)
A. 228w B. 224X
c. 222y D. 22oz
T4. Which of the following processes would involve neutrino, or anti-neutrino, production? A. a decay B. ~decay C. Isomeric transition D. Positron-electron annihilation
TS. In stable isotopes of heavy nuclei: A. The number of protons equals the number of neutrons. B. The number of protons is higher than the number of neutrons. C. The number of neutrons is higher than the number of protons. D. The numbers of neutrons and protons are unrelated. E. The number of electrons equals the number of neutrons.
T6. If there is a malfunction in a linear accelerator (linac) such that the electron scattering foil is NOT positioned in the beam, then the central axis dose rate will be too:
A. High, by <10%. B. High, by >50%. C. Low, by <10%. D. Low, by >50%.
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therapy questions
T7. In a linear accelerator, to produce the same dose rate for a 15 MV x-ray beam as for a 6 MV x-ray beam, the electron current in the accelerating cavity must be:
A. Higher for 15 MV than for 6 MV. B. Higher for 6 MV than for 15 MV. C. About the same for both energies.
T8. In a linear accelerator, to produce the same dose rate for a 15 MV x-ray beam as for a 15 MV electron beam, the electron current in the accelerating cavity must be:
A. Higher for electron treatment than for photon treatment. B. Lower for electron treatment than for photon treatment. C. About the same for both modalities.
T9. For a 15 MV electron beam, most of the x-ray contamination comes from electron interactions in the:
A. Scattering foils. B. Flattening filter. C. Electron applicators and collimators. D. Patient.
T I 0. Tungsten has electron shell binding energies of: K = 69 ke V, L = 12 ke V, M = 2 ke V. A 60 keV electron striking a tungsten target could cause emission of characteristic x-rays of which of the following energies (ke V)?
A. 69,60,9 B. 69,12,2 C. 60,12,2 D. 10,2
T I I. Which beam modality has the highest neutron-contamination dose? A. 6 MV x-rays. B. 15 MV x-rays. C. 6 MeV electrons. D. 15 MeV electrons. E. None of the modes listed above can generate neutrons.
T 12. The sharpest beam edge penumbra for a linac MV x-ray beam is achieved when the field edge is defined by:
A. The collimator x-y jaws. B. A multileaf collimator. C. A custom-designed lead or metal alloy field block. D. None of the above. Penumbra is the same for all three of these devices.
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therapy questions
T 13. If the filtration of a diagnostic x-ray beam is increased, the resulting beam will have: A. Lower dose rate and greater HVL. B. Higher dose rate and higher effective energy. C. Lower dose rate, but the same HVL. D. Same dose rate, but a lower HVL. E. Same dose rate, but a greater HVL.
T 14. In a medical linear accelerator, which of the following is the correct arrangement of components 1-5 as "seen" by the beam: 1. Primary collimator 2. Jaws and secondary collimator 3. Target 4. Ion chamber 5. Flattening filter
A. 5, 3, 4, 1, 2 B. 3, 1, 2, 5, 4 c. 3, 1, 5, 4, 2 D. 4,3, 1,5,2
TIS. Which of the following does NOT occur when a linac is changed from the x-ray mode to the electron mode?
A. The target is removed. B. A scattering foil is placed in the beam. C. The monitor chamber is removed. D. An electron applicator is attached. E. The beam current decreases.
T 16. Flattening filters in photon beams are designed to optimally flatten the beam at a depth of: A. dmax· B. 5 em. C. 10 em. D. 20 em.
Tl7. If0.5 mm of lead attenuates an x-ray beam by 91%,0.25 mm oflead will be expected to attenuate what percent of the radiation?
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A.lO B. 20 c. 35 D. 70 E. 99
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therapy questions
T 18. A 10 MeV photon undergoes a Compton interaction, and the scattered photon is emitted perpendicular to the direction of the incident photon. What is the approximate energy of the scattered photon?
A. 0.51 MeV B. 1.02 MeV C. 1.25 MeV D. 2.04MeV
Tl9. A 50 keV x-ray has a photoelectric interaction with an atom. The emitted electron has a kinetic energy of 34 keV. Immediately, a 10 keV characteristic x-ray is emitted. What was the binding energy of the electron?
A. 6 keV B. 16 keV C. 24 keV D. 26 keV
T20. For a mega voltage beam of photons utilized in radiation therapy, the dominant mechanism of attenuation in muscle tissue is:
A. Pair production. B. Coherent scatter. C. Photoelectric. D. Compton interaction. E. None of the above.
T21. The photon interaction that produces the difference in density between barium and soft tissue on a CT image is:
A. Coherent scatter. B. Photoelectric effect. C. Compton scatter. D. Pair production. E. Photonuclear disintegration.
T22. Portal images taken on a radiotherapy linac are typically acquired with a 6 MV x-ray beam. Which best describes the interactions of the incident x-rays in a patient's body?
A. Mostly photoelectric absorption with some Compton scattering B. Mostly Compton scattering with some photoelectric absorption C. Mostly Compton scattering with some pair production D. Mostly pair production with some Compton scattering
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therapy questions
T23. For the same nominal 6 MV x-ray beam energy, which of the following beams has the most penetrating depth dose?
A. Beam with a flattening filter but no wedge B. Flattening filter free (FFF) beam, but with no wedge C. Beam with flattening filter plus "hard" wedge D. Beam with flattening filter plus "dynamic" wedge E. FFF beam plus "hard" wedge
T24. Flattening filter free (FFF) x-ray beams: A Deliver dose rates at least twice that of conventional beams for all field sizes up to
40x40 cm2•
B. Significantly improve dose distributions. C. Have a higher average energy than a conventional beam. D. None of the above.
T25. If the flattening filter in an MV x-ray beam is not correctly centered, the beam will: A. Be symmetrical but not "flat." B. Be "flat" but not symmetrical. C. Have a slightly different central axis depth dose. D. None of the above.
T26. For 6 MV x-rays, the absorbed dose is different in fat, muscle, and bone. Arrange these three tissues in order of increasing absorbed dose:
A. Fat, Muscle, Bone. B. Fat, Bone, Muscle. C. Bone, Fat, Muscle. D. Bone, Muscle, Fat. E. Muscle, Fat, Bone.
T27. For 20 MV x-rays, the absorbed dose is different in fat, muscle, and bone. Arrange these three tissues in order of increasing absorbed dose:
A. Fat, Muscle, Bone. B. Fat, Bone, Muscle. C. Bone, Fat, Muscle. D. Bone, Muscle, Fat. E. Muscle, Fat, Bone.
T28. In comparing two 6 MV x-ray beams, both 100 cm2 in total area but one having lOxlO cm2
collimator setting and the other 5x20 cm2, what can be said about the relative doses at dmax?
A. The primary dose is higher for a lOxlO field. B. The scatter dose is higher for a lOxlO field. C. Both the primary and scatter doses are higher for a lOxlO field. D. The doses for the two fields will be the same.
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therapy questions
T29. Which of the following will affect the penumbra width of a therapy beam? A. Composition of the jaws B. Dose rate C. Gantry angle D. Distance between target and collimator
T30. The average leakage dose from the multileaf collimator (MLC) relative to the primary dose is approximately %.
A. 0.1--0.5 B. 1-2 c. 3-5 D. 5-10
Tll. Which choice is NOT appropriate for external beam in vivo dosimetry? A. Diode B. TLD (Thermoluminescent Dosimeter) C. OSLD (Optically Stimulated Luminescence Dosimeter) D. Geiger Counter
T32. Which type of dosimeter would NOT typically be used to measure the neutron contamination in a proton therapy beam?
A. Bubble detector B. Parallel-plate ionization chamber C. Lithium fluoride TLD-600 plus TLD-700 D. Bonner sphere
T33. A 6 MV x-ray beam is calibrated by placing a Baldwin Farmer ionization chamber at <Imax in a tissue-equivalent phantom of total thickness 3 em. The ion chamber will read slightly lower than the correct value because:
A. A Baldwin Farmer chamber can only be used for electron beams, not x-ray beams. B. A 3-cm thick phantom is insufficient to establish full backscatter dose. C. There is electron contamination of the beam at <Imax· D. There will be ion recombination at dmax·
T34. Portal dosimetry using EPIDs refers to all of the following except: A. Dose profile measurement. · B. IMRTQA. C. Patient position verification. D. MLC alignment verification. E. Fluence distribution map.
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therapy questions
T35. The advantages of radiochromic film, as compared with radiographic film, for purposes of x-ray and electron dosimetry include all of the following, except:
A. It is nearly tissue equivalent. B. It does not require post-irradiation processing. C. It is relatively insensitive to visible light. D. Its response (optical density vs. absorbed dose) is more linear. E. It requires a lower dose.
T36. A thimble-type ionization chamber that was calibrated at standard temperature and pressure is used to calibrate a linear accelerator beam at ambient temperature of 25 °C and pressure of 780 mm Hg. If no temperature-pressure correction is made, the chamber reading will be:
A. Too high. B. Too low. C. Correct.
T37. All of the following are true of optically stimulated luminescence dosimeters (OSLDs), except: A. Can be used for in vivo dose measurement. B. Heat is used to release and measure trapped energy. C. Amount of light measured is proportional to amount of radiation absorbed. D. Minimal energy dependence in the therapy range.
T38. An MLC "picket fence" test is a quality assurance test for which of the following MLC properties?
A. Leakage through the leaves B. MLC leaf spread C. Alignment of MLC with central beam axis D. MLC leaf positioning accuracy E. All of the above
T39. When evaluating the quality of a treatment plan, which of the following is usually not considered?
A. Isodose distributions conforming to shape of PTV. B. Meeting clinical dose constraints for normal tissues. C. Beam arrangement. D. Total number of monitor units.
T40. When CT images are used for radiotherapy planning, Hounsfield numbers must be converted to electron densities for use by the dose calculation algorithms. The relationship between Hounsfield number and electron density is approximately linear for most tissues except:
A. Bone. B. Lung. C. Air cavities. D. Muscle.
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therapy questions
T 41. All of the following are advantages of a dynamic wedge over a physical wedge, except: A. Approximately same central axis depth dose as an open beam. B. Field height is not limited. C. Therapists do not have to lift a heavy wedge. D. Less dose outside the field (e.g., to contralateral breast). E. Wedge transmission factor is independent of field width.
T42. In a cumulative lung dose-% volume histogram, V20 refers to: A. The % lung receiving at least 20 Gy. B. The% lung receiving exactly 20 Gy. C. The % lung receiving less than 20 Gy. D. The dose to 20% of the lung volume.
T43. Which of the following quantities cannot be determined from a target dose-volume histogram? A. Maximum target dose B. Minimum target dose C. Dose to the hottest 95% of the target D. Location of the target hot-spot
T 44. One method for assessing the quality of a head and neck treatment plan is to evaluate which of the following dose parameters to the parotid glands and spinal cord?
A. The mean parotid dose and maximum spinal cord dose. B. The maximum parotid dose and the maximum spinal cord dose. C. The mean parotid dose and the mean spinal cord dose. D. The maximum parotid dose and the mean spinal cord dose.
T45. A large head and neck tumor noticeably shrinks during the course of radiotherapy, but the treatment plan is not modified. Which of the following is NOT true?
A. The delivered spinal cord dose may be higher than planned. B. The mean parotid dose may be higher than planned. C. The immobilization device may lose its effectiveness. D. The monitor units may decrease. E. The hot spot in the tumor may increase.
T46. Which of the following dose calculation algorithms is the least accurate for treatment planning of a lung lesion?
A. Pencil beam B. Collapsed cone C. Convolution and Superposition D. Monte Carlo
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therapy questions
T47. For the same delivered dose, which statement below is false? The MUs for a: A. Dynamic wedge are higher than for an open field. B. Physical wedge are higher than for an open field. C. Universal wedge are higher than for an open field. D. Dynamic wedge are higher than for a physical wedge.
T48. When treating a 3-field chest wall using the mono-isocentric technique, which is true? A. Collimator rotation is needed. B. Couch kick away from the gantry is needed. C. Couch kick towards the gantry is needed. D. A beam-splitter block is needed.
T49. Which of the following is false? The skin dose, as a percentage of dose at dmax• in a 6 MV photon beam will increase when:
A. The SSD is decreased. B. The field size is decreased. C. Bolus is used. D. Fields are treated at oblique incidence.
TSO. A craniospinal axis requires two adjacent fields matched at 5.5 em depth, set up at 100 em SSD. The collimator settings are 30.0 em and 24.0 em. The gap on the skin is em.
A. 0.7 B. 1.2 c. 1.5 D. 2.2 E. 3.0
TS I. Which of the following delivers the greatest scatter dose to the contralateral breast from a medial tangential breast field?
A. A universal wedge. B. A dynamic wedge. C. A physical (metal) wedge. D. All of the above are about equal.
TS2. A prostate cancer patient has a defibrillator/pacemaker. Because of concerns about neutron contamination in the 18 MV beam, it is decided to treat him with 6 MV. Which statement best describes the effects of using the 6 MV beam?
A. The total MUs will be lower for the 6 MV plan. B. The in-field hot spot close to the skin will be lower for the 6 MV plan. C. The 6 MV high isodoses will conform better to the shape of the prostate. D. None of the above.
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therapy questions
TSJ. T53. When treating a small tumor on the lower eyelid [size approximately 0.6 em (w) x 0.6 em (1) x 0.4 em (d)] with 6 MeV electrons, which of the following is true?
A. A lead mold placed on the patient's skin surface should be shaped very tightly to the lesion size without additional margin.
B. No bolus is required. C. The isodose lines will lie closer to the patient surface than for a larger field. D. MU will be lower than for an unblocked field.
TS4. The electrons for a linac are calibrated using a 100-SSD setup and 10x10 cone. For a 180 cGy prescription to the 90% isodose with 100 SSD and 1 Ox 10 cone, the total number of MU required is approximately __ _
A. 160 B. 180 C. 200 D. 220
TSS. The skin dose for a 6 MeV electron beam is lower than for a 15 MeV electron beam because for the 6 MeV beam there is:
A. More range straggling. B. Less range straggling. C. More x-ray contamination. D. Lower linear energy transfer (LET).
TS6. An electron energy of ___ MeV would be most suitable for treating a PTV extending to 3 em below the surface.
A. 6 or 9 B. 9 or 12 C. 12 or 16 D. 16 or 20 E. 20 or greater
TS7. A 6 MeV electron beam passes through 2 em of tissue, overlying lung (density 0.25 g/cm3).
The approximate range in the patient is em. A. 1 B. 3 c. 6 D. 9 E. 12
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therapy questions
T58. As a rule of thumb, ___ mm of low melting alloy is(are) required per MeV to shield an electron beam.
A. 2.0 B. 1.0 C. 0.6 D. 0.2
T59. An electron beam enters a patient's surface obliquely. All of the following can be expected, except:
A. The surface dose increases. B. The depth of dmax decreases. C. The depth of the 90% isodose decreases. D. The depth of the 50% isodose increases.
T60. Bolus material is often used for electron beam treatments in order to increase the skin dose. For oblique incidence the thickness of bolus required as compared to perpendicular incidence is:
A. Thicker. B. Thinner. C. The same. D. Bolus should not be used for oblique beams.
T61. According to AAPM Task Group 51 report, output measurements in water have to be performed: A. Daily. B. Monthly. C. Quarterly. D. Yearly.
T62. AAPM Task Group 142 report introduced the following new weekly check: A. Water tank measurements. B. Couch sag consistency. C. MLC alignment. D. Gantry angle accuracy. E. Vertical couch travel.
T63. For linacs equipped with kV imaging systems, the AAPM Task Group 142 report recommends that the geometrical alignment of the kV imaging system with the MV therapy beam be checked:
A. Daily. B. Weekly. C. Monthly. D. Annually.
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therapy questions
T64. A patient is to be treated with 6 MV photons at 100 em SAD to a depth of 6 em with a 10x10 em field. The calculation is done in error using a depth of 8 em. The magnitude of error in dose delivered to the isocenter is approximately %.
A. <1 B. 3 c. 7 D. 12 E. 20
T65. The most widely used protocol for transferring digital images between devices is: A. DICOM. B. BHL7. C. CIFS. D. XML. E. XDS.
T66. The most useful parameter directly measurable in a PET scan is: A. HU. B. SUV. C. Size of an abnormality. D. None of the above.
T67. The following quantity is considered PHI (Protected Health Information): A. The year an event related to a patient occurred. B. The accession number of an exam. C. The Medical Record Number (MRN) assigned to the patient. D. The state in which the patient was treated.
T68. A new linac is to be installed in an old treatment vault built approximately 10 years ago. At the time, all radiation safety specifications were met. The new linac has flattening filter free (FFF) beams, high-dose-rate SRS beams, and will be used mostly for IMRT, SRS, and SBRT. The room shielding should be checked because:
A. The workload may be more than originally designed for. B. The maximum hourly dose rate may be more than originally designed for. C. The maximum beam energy may be more than originally designed for. D. All of the above.
T69. Current estimated population average annual radiation exposure in the United States is: A. Less than 1 mSv. B. About 1 mSv. C. About 3 mSv. D. About 6 mSv. E. More than 10 mSv.
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therapy questions
T70. Which of the following are necessary to estimate shielding requirements for an x-ray room? A. Workload B. Use factor C. Occupancy D. Distance E. All of the above
T71. According to NRC regulations, if an x-ray technologist declares her pregnancy, what is the legal limit on the total dose to the embryo/fetus?
A. 500 mSv B. 50 mSv C. 5 mSv D. 0.5 mSv
T72. All of the following studies have demonstrated an increased risk of radiation-induced cancers, except:
A. Atomic bomb survivors. B. Chest fluoroscopy for tuberculosis. C. Diagnostic bone scans. D. Radium dial painters. E. Radiation therapy.
T73. The radiation dose limit for a patient undergoing a PET scan with 18F-FDG is: A. 50 mSv. B. 20 mSv. C. 15 mSv. D. 5 mSv. E. Not limited.
T74. In radiation shielding design, the weekly radiation dose to the uncontrolled areas should NOT exceed mSv.
A. 0.01 B. 0.02 c. 0.05 D. 0.1 E. 0.5
T75. According to the ALARA principle, the weekly radiation dose to controlled areas should NOT exceed mSv.
A. 0.02 B. 0.05 C. 0.1 D. 0.5 E. 1
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therapy questions
T76. When designing a PET/CT suite shielding, which of the following is the most important factor in determining the amount of lead required?
A. CTmAs B. Scatter dose from the CT scanner C. Gammas emitted from the patient D. CT tube voltage
T77. A patient is treated on a linac with a different patient's treatment plan, but the delivered dose was within 10% of the correct value and the error was discovered immediately upon completion of treatment. Does this have to be reported as a "medical event"?
A. No, because no harm was done to the patient. B. No, because the mistake was discovered immediately. C. No, because the error in delivered dose error was <20%. D. Yes, because this is considered "treatment to wrong patient."
T78. An 192Ir HDR unit can safely be installed without the need for any additional shielding in which of the following types of rooms?
A. A CT scanner room B. A PET scanner room C. A linac vault D. A gamma camera room
T79. For scattered and leakage radiation from a linear accelerator, the usage factor (U) in shielding calculations is set to __ _
A. 0 B. 0.25 C. 0.50 D. 1.0
T80. According to NCRP recommendations, what is the dose limit for the general public in corridors or waiting rooms adjacent to an x-ray room?
A. 50 mrem/y B. 1 mSv/y C. 50 !lGy/y D. 0.005 mSv/y E. 0.02 mSv/h
T81. According to NCRP, patients receiving therapeutic amounts of radioactive material may be released from the facility if the total dose to a member of the public is maintained below the following:
A. 50 mSv. B. 5 mSv. C. 1 mSv. D. 1 mrem.
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therapy questions
T82. Which linac-based imaging technique provides the best low-contrast resolution? A. Megavoltage portal image B. Cone-beam CT C. Kilovoltage projection image D. kV-MV image fusion
T83. All of the following techniques are commonly used for IGRT (image-guided radiotherapy) patient setup of the prostate, except:
A. Pretreatment orthogonal pair of kV radiographic images. B. Pre-treatment cone-beam CT (CBCT) to visualize soft tissue. C. Implanted radiofrequency beacons. D. EPID dosimetry.
T84. Which of the following is NOT used in an amorphous-silicon flat-panel imaging system? A. A large area pixelated array B. A series of mirrors, lens, and camera C. A control and acquisition system D. An x-ray converter
T85. For a non-gated lung treatment, a CBCT image can be acquired to assist with patient setup. The CBCT will be most similar to the:
A. Inhale phase of a 4DCT scan. B. Exhale phase of a 4DCT scan. C. Average image of a 4DCT scan. D. Maximum intensity projection image (MIP).
T86. A cone-beam scan is used to position a patient for treatment. When comparing the cone-beam scan to a pair of orthogonal kV images, which of the following is true? The cone-beam scan:
A. Delivers a greater integral dose to the patient. B. Can be acquired, reconstructed, and evaluated in less time. C. Has poorer soft-tissue resolution. D. Is less subject to artifacts caused by patient motion.
T87. The radiation dose in air from a single cone-beam CT is typically: A. 1-5 mGy. B. 10-50 mGy. C. 100-500 mGy. D. >1 Gy.
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therapy questions
T88. The radiation dose in air from a single kV-image is typically ___ mGy. A. 0.1--0.5 B. 1-5 c. 10-50 D. 100-500
T89. The image-guided radiotherapy (IGRT) technique that imparts the least dose is: A. Cone-beam CT with gantry-mounted kV source/detector. B. Cone-beam CT with MV treatment beam. C. Planar kV radiographs. D. Planar MV radiographs.
T90. Continuous tracking of prostate motion during fixed-gantry IMRT delivery can be accomplished by:
A. Cone-beam CT with gantry-mounted kV source/detector. B. Cone-beam CT with MV treatment beam. C. Stereoscopic optical camera system. D. Stereoscopic infrared camera system. E. Implanted RF electromagnetic beacon localization.
T91. For the same imaging dose and energy, the image quality of CBCT acquired using a flat-panel imager on a linear accelerator is poorer than that using a CT scanner mainly because:
A. CT reconstruction algorithm is better. B. CBCT has more scattering than CT. C. CT images use more bits per pixel. D. CBCT's slice thickness is larger.
T92. IGRT can be done using MV CBCT and/or kV CBCT. In what situations might MV CBCT produce a better quality image?
A. When imaging soft tissue B. When imaging bony anatomy C. When there are metallic objects present in the scanned region D. None of the above
T93. What is the typical range of acceptable table shifts after performing a CBCT 3D/3D matching or kV 2D/2D matching?
A. 0-2mm B. 2-7 mm C. 5-20mm D. >20mm
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therapy questions
T94. Most linac EPIDs (electronic portal imaging devices) comprise three separate layers. A thin metal sheet, a scintillator or phosphor, and charge collecting layer as shown in the schematic below.
Photon Beam
In which layer do most of the x-ray interactions occur? A. Metal screen B. Phosphor screen C. Charge collecting layer
T95. Which of the following is NOT an advantage of 3T magnetic resonance imaging scanners relative to 1.5T systems?
A. Lower distortions B. Increased signal to noise C. Increased separation of spectrum peaks D. Increased susceptibility effects
T96. A prostate patient has a course of treatment that will involve a setup based on a single conebeam scan for each of his 40 treatment days. The approximate dose to the prostate that the patient will receive from the cone-beam imaging alone is:
A. 0.6 mGy. B. 6 mGy. C. 6 cGy. D. 60 cGy. E. 6Gy.
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T97.
T98.
T99.
TIOO.
TIOI.
18
A cone-beam scan is taken to set up a cranium in an image-guided SRS procedure. The IGRT software is capable of calculating both 3D and 6D couch/corrections. The couch being used for treatment, however, is only capable of implementing 3D corrections. The calculated corrections for 3D and 6D are different. What is the best course of action?
A. Report a bug in the software. B. Use the 6D correction factors. C. Use the 3D correction factors. D. Use the average of the two sets of translations.
In commercial amorphous-silicon flat-panel imaging systems, which of the following is the primary means of detection in the pixelated array layer?
A. Conversion of x -rays into electron-hole pairs B. Conversion of electrons into visible light C. Conversion of x-rays into high-energy electrons D. Conversion of visible light into electrical charge
Which beam-modifying device is used for kV cone-beam CT generation? A. Wedge B. Graticule tray C. Bow-tie filter D. ·Electron applicator E. Custom-shaped photon block
A patient has a head CT using a 30-cm field of view (FOV). What is the approximate size of each pixel (i.e., x or y dimension) on each transverse image?
A. 0.2mm · B. 0.6mm C. 1.0 mm D. 1.2 mm
In formulating an appropriate CTV-to-PTV margin, all of the following should be considered, except:
A. Frequency and type of image guidance. B. Frequency and type of intrafraction motion monitoring. C. Type of immobilization device used. D. Patterns of microscopic spread for this disease type and anatomical site. E. The uncertainty in the coincidence of the imaging and radiation isocenters in the
treatment room.
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TI02.
TIOJ.
TI04.
TIOS.
TI06.
therapy questions
Gold marker seeds are implanted into a prostate to facilitate accurate image-guided daily patient setup. The minimum number of seeds that must be implanted in order to unambiguously determine both prostate x-y-z coordinates plus possible prostate rotation is( are):
A. 1 seed. B. 2 seeds. C. 3 seeds. D. 4 seeds.
A patient is being treated with 15 MV photons on an accelerator with 6 MV and 15 MV beams. Portal images are acquired with an EPID to verify the isocenter. Which energy should be used for imaging?
A. 15X, because it is the treatment energy. B. 15X, because patient dose will be lower. C. 6X, because image quality will be slightly superior. D. 6X, because patient dose will be lower.
All of the following could be sources of systematic error in a patient's treatment, except: A. Offset between positioning lasers in simulator versus treatment room. B. Differences in sag between CT simulator couch and linac couch. C. Daily variations in internal anatomy near the PTV. D. Error in target delineation. E. Misplacement of setup tattoos during simulation.
Differing interpretations between physicians as to the proper anatomical boundaries in the delineation of a target is referred to as:
A. Setup error. B. Intra-observer error. C. Inter-observer error. D. Contouring error. E. None of the above.
Fiducial markers may be implanted into soft tissue to assist with radiographic localization. Which of the following is occasionally observed in radiographs taken several weeks after implantation?
A. Markers may shift relative to bony anatomy. B. Markers may shift relative to each other. C. Markers may migrate out of the implanted organ. D. All of the above. E. None of the above.
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therapy questions
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In formulating an appropriate GTV-to-CTV margin, which of the following factors should be considered?
A. Frequency and type of image guidance. B. Frequency and type of intrafraction motion monitoring. C. Type of immobilization device used. D. Uncertainty in the coincidence of the imaging and radiation isocenters in the treatment
room. E. None of the above.
A treatment using volumetric arc therapy (VMAT) usually requires fewer monitor units than does the same treatment with static gantry intensity modulation (i.e., IMRT). This is because:
A. On average the MLC leaf openings are larger for VMAT than for IMRT. B. On average the dose rate is higher for VMAT than for IMRT. C. On average the treatment depth is less for VMAT than for IMRT. D. None of the above.
Intensity-modulated radiotherapy optimization computer algorithms methods include all of the following, except:
A. Step-and-shoot. B. Gradient search. C. Simulated annealing. D. Direct aperture optimization.
What is the cause of tongue-and-groove effect for MLC-based IMRT? A. Leaves that are moving too slowly B. Leaves that are out of calibration C. Adjacent leaves that extend into the field by very different amounts D. Opposing leaves that are closed, but are not under the jaw E. Leaves with rounded edges
Which factor will likely increase the MU for an IMRT field? A. Switching from 1 em to 5 mm leaf widths B. Switching from a sliding window delivery to a step-and-shoot delivery C. Adding additional critical structures in the dose optimizaton D. Using a leaf transmission factor in the TPS that is too high
Which of the following is unique to IMRT and never used for 3D CRT? A. Non-uniform beam intensities B. Inverse planning for dose-volume constraints optimization C. Multileaf collimators D. CT-based treatment simulation
Raphex 2012
Till.
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therapy questions
The treatment planning algorithm that constructs a VMAT delivery sequence must consider all of the following, except:
A. Maximum gantry rotation speed. B. Maximum MLC leaf speed. C. Maximum linac dose rate. D. Prescribed dose per fraction. E. Prescribed number of fractions.
For a total body irradiation (TBI) treated at 3.0 m from isocenter using a linac, the output at dmax in the patient is about cGy/MU (assuming 1.0 cGy/MU at dmax• 100 SSD).
A. 3.0 B. 1.0 C. 0.25 D. 0.06
The advantages of treating TSEB using pairs of slightly angled beams (i.e., ±20° above and below horizontal) instead of single horizontal beams include all of the following, except:
A. Taller patients can be treated. B. Reduced x-ray contamination dose to the patient. C. More uniform dose distribution. D. Shorter total treatment times.
What is the minimum recommended total arc length for volumetric modulated arc therapy (VMAT) treatments:
A. 90° B. 360° c. 720° D. None of the above. Plan generally does not depend upon the total arc length.
Volumetric modulated arc therapy (VMAT) usually refers to: A. Arc treatments with static photon fields. B. Arc treatments with static electron fields. C. Linac-based radiosurgery. D. Intensity-modulated photon field delivered with the gantry in motion. E. Intensity-modulated electron field delivered with the gantry in motion.
Which linac parameter(s) affect the total delivery time for volumetric modulated arc therapy (VMAT)?
A. Maximum dose rate B. Maximum MLC leaf speed C. Maximum speed of gantry rotation D. All of the above
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therapy questions
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"Patient-specific" dosimetry confirmation for a volumetric modulated arc therapy (VMAT) treatment plan is sometimes done by placing a 2D detector array in the blocking tray of the linac and measuring the ensuing isodose distribution during treatment delivery. Such a technique may fail to detect the following error:
A. Incorrect central axis dose. B. Incorrect beam energy. C. Incorrect correlation between MLC leaf positions and gantry rotation angle. D. Incorrect file down loaded to linac.
If the dose rate under a 1 em diameter SRS treatment cone is calibrated using a Farmer ionization chamber, delivered treatment doses to patients treated with this cone will be:
A. Too low. B. Correct. C. Too high.
Regarding single-fraction total body irradiation (TBI): A. The dose rate should be relatively high (> 1 Gy/min) to keep the treatment time as short
as possible. B. The dose rate should be low (<0.2 Gy/min) to minimize the side effects. C. If the treatment is delivered from two lateral fields, electron boost fields are sometimes
used for the chest wall. D. The dose should be at least 20 Gy.
According to AAPM TG-54 report, which of the following QA procedures are recommended before the delivery of SRS treatment using stereotactic collimator cones?
A. Wendell-Lutz alignment test performed on the linac B. Treatment plan monitor units verified by second person or technique C. Linac jaws set to a field size = 5 em x 5 em D. Plan approved and signed by Radiation Oncologist E. All of the above
A brachytherapy treatment plan calculation is based on measurements taken from orthogonal x-ray films taken of the implant. The magnification factor calculated for the films is erroneously determined to be larger than the true value. Delivered treatment dose to the patient treated with this implant will be:
A. Too low. B. Correct. C. Too high. D. Cannot be determined from the data given.
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therapy questions
In order to deliver uniform dose at 5 mm from the surface of an HDR treatment using a vaginal cylinder, the source dwell times should be:
A. Longer at the ends than in the middle. B. Longer in the middle than at the ends. C. About the same at all positions.
The isodose distribution around a typical 125I brachytherapy 'seed is asymmetric because: A. X-rays are preferentially emitted in the forward direction. B. 125I emits electrons rather than x-rays. C. X-ray attenuation varies in different parts of the metal casing. D. None of the above. The dose distribution is symmetric.
The dose vs. distance within 5 em from an 192Ir source is very close to the inverse square law despite gamma ray absorption because:
A. Increasing scatter dose compensates for beam attenuation. B. 192Ir emits x-rays of several different energies. C. Of attenuation by the metal seed casing. D. Beam attenuation is negligible within 5 em for an 192Ir source.
Patterson Parker (PP) rules cannot be used for calculation of dose distributions for a 103Pd brachytherapy implant because:
A. PP was designed for radium, which has much higher energy than 103Pd. B. PP was designed for radium, which has much lower energy than 103Pd. C. 103Pd emits mostly x-rays instead of gamma rays. D. 103Pd has a much shorter half life than does radium. E. None of the above. PP can be used for calculating 103Pd dose.
HDR treatment planning systems usually do not account for transit dose (dose given while the source is in transit). A plan is calculated with source dwell times adjusted for each fraction to account for the source decay. Which of the following statements is true?
A. The transit dose will increase as the source decays. B. The transit dose is constant for all fractions. C. The transit dose will decrease as the source decays.
A patient is beginning a series of HDR fractions of equal dose. The same plan is used throughout. Initially the source activity is 200 GBq and the total treatment time is 200 seconds. At the final treatment, the activity is 160 GBq. What is the total time, in seconds, for this final treatment?
A. 160 B. 200 C. 240 D. 250
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therapy questions
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A potential prostate seed implant patient undergoes a transrectal ultrasound (TRUS) to determine prostate volume. The height, width, and length of the gland are measured. The volume of the gland can be computed approximately by assuming it has the shape of a(n):
A. Cube. B. Brick. C. Cone. D. Ellipsoid.
According to AAPM recommendations, quality assurance of multi-channel intracavitary HDR applicators for breast includes:
A. Daily CT scan. B. Daily check of the balloon volume and consistency of the applicator position. C. Check of each channel length prior to each treatment. D. All of the above.
A permanent lung implant using 125I seeds is intended to deliver a total dose of 100 Gy. The initial dose rate is cGy /h.
A. 7 B. 1.7 c. 4.9 D. 17.0
The type of electromagnetic energy used for hyperthermia treatments is: A. X-ray. B. Ultraviolet. C. Visible light. D. Infrared. E. Microwave.
The typical desired treatment temperature for hyperthermia is: A. 37 °Centigrade. B. 37 °Kelvin. C. 37 °Fahrenheit. D. 45 °Centigrade. E. 60 °Centigrade.
For treatment planning purposes, the RBE of protons is usually assumed to be __ _ A. 0.9 B. 1.0 c. 1.1 D. 2.0
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therapy questions
For proton therapy, the effects on dose distribution of inhomogeneities compared to photons are:
A. Larger. B. Smaller. C. The same.
Methods for producing large proton treatment fields include: A. Double scattering. B. Uniform scanning. C. Pencil beam scanning. D. All of the above. E. None of the above.
The therapeutic energy range of protons is: A. 30-250 MeV. B. 6-18 MeV. C. 0-500 MeV. D. None of the above.
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