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preface The RAP HEX Therapy exam 2010 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. There are now two exams, Diagnostic and Therapy, each with about 130 questions, including general physics questions appropriate to the specialty. Exam committee: Doracy Fontenla, Ph.D., Editor Susan Brownie, M .Sc., Reviewer Howard Amols, Ph.D., Reviewer Eugene Lief, Ph.D., Reviewer Richard Riley, Ph.D., Reviewer Contributors: Alex Kapulsky, Ph.D. John Keane, M.Sc.Abishek Dwedi, M.Sc. John Napoli, M.Sc. John Humm, Ph.D. Lawrence Dauer, Ph.D. Ruimei Ma, Ph.D. Sandra Fontenla, M.Sc. Dale M. Lovelock, Ph.D. Yeh Chi-Lo, Ph.D. Chen-Shou Chui, Ph.D. Shantini Rajaratnam, 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. Rap hex Chief Editor E-mail: [email protected] Copyright © 2010 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-4.

Match the following (answers may be used more than once): A. Electrons. B. Protons. C. Neutrons. D. Neutrinos. E. Gamma rays. Responsible for nuclear medicine imaging with 99mTc. Responsible for MR imaging. Most difficult to detect. Emitted in beta minus decay with antineutrinos.

Tl. T2. T3. T4.

TS.

In stable isotopes with 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.

T6.

Which A. B. C. D.

T7-IO.

Match the elementary particle, as described by its characteristics below, to the following description. (Answers may be used more than once.) A. B. C. D.

T7. T8. T9. TlO. T II.

of the following is true? Iodine-131 and Iodine-125 _ __ Have different chemical properties Have different Z values Have the same number of neutrons None of the above.

Charge +1 +1 0 -1

Rest Mass 0.51 MeV 938 MeV 940MeV 0.51 MeV

Is the nucleus of a hydrogen atom. Is responsible for x-ray production in CT scanners and linear accelerators. When this particle combines with an electron, annihilation photons are emitted. There are 2 ofthese in a Tritium nucleus.

Which one of the statements below is true for the characteristic x-ray.s emitted from a tungsten target when 100 keV electrons are fired at it: A. Have a continuous spectrum of energies up to 100 keV. B. Are about equal in intensity to the bremsstrahlung. C. Have energies equal to differences in the electron binding energies of tungsten. D. Do not contribute to the imaging process. E. Have a non-isotropic distribution.

Raphex 2010

therapy questions J" 12.

Increasing the kVp of an x-ray beam without changing any other control setting will increase all of the following, except: A. Amount of heat produced at the anode. B. Intensity of the x-ray beam. C. Exposure to a person in the room out of the direct beam. D. Contrast in a film taken at the higher kVp.

T 13.

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.

T 14.

What tests should be performed daily on a CT Simulator in a radiation therapy department? A. Laser accuracy B. Constancy of CT-to-density conversion for treatment planning software C. Half-value layer determination D. Optical Distance Indicator accuracy E. All ofthe above

T 15.

Which of the following does not utilize electromagnetic radiation? A. Diagnostic x-rays B. Positron emission tomography C. Gamma camera D. B-mode ultrasound E. Gamma knife

T 16.

Which of the following does not occur when a linac is changed from the x-ray mode to the electron mode? (Excluding units with scanned electron beams) 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.

Tl7.

In linacs which use flattening filters, which of the following is false? A. It must be carefully centered on the beam axis. B. It is needed to convert a narrow, forward peaked beam into a more useful broad, fiat beam. C. The same filter is used for the 6 MV photon beam and the 6 MeV electron beam. D. It can become radioactive, depending on beam energy. E. Flattening filters create "horns" at ~ax·

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therapy questions T 18.

Bending magnets are needed in high-energy linear accelerators: A. To rotate the electron beam so that it points towards the isocenter. B. Only in the photon mode. C. Only for linacs with the waveguide mounted perpendicular to the gantry rotation axis. D. Only in the electron mode. E. Only with dual-energy photons.

T 19.

When a linear accelerator is used in the electron n1ode, the electron beam passes through each of the following components, except: A. Accelerator wave guide. B. Bending magnet. C. Target. D. Primary collimator. E. Monitor chamber.

T20.

Neutron contamination is greatest in a A. Co-60 B. 6 MV photon C. l 0 MV photon D. 20 MV photon E. 20 MeV electron

T21.

Which is the predominant reaction by which fast neutrons dissipate energy in tissue? A. Neutron capture by hydrogen giving rise to 2.2 MeV y-rays by the (n, y) reaction B. Elastic collisions with hydrogen nuclei (protons) present in the tissue C. Inelastic collisions with heavier nuclei, resulting in disintegration, of which the reaction with nitrogen giving rise to a proton of0.66 MeV is the most important D. Elastic collisions with heavier nuclei present in tissue

T22.

Which of the following is a directly ionizing radiation? A. 2 MHz ultrasound B. 6°Co gammas C. 90Sr betas D. 15 MeV photons E. Thermalneutrons

T23.

All of the following are properties of electromagnetic radiation, except: A. Obeys the inverse square law for point source. B. Travels at a constant velocity in a vacuum. C. Can be deflected by a magnetic field. D. Is exponentially attenuated by a medium. E. Is composed of perpendicular electric and magnetic fields.

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therapy questions T24.

In the interaction of ionizing radiation and matter, absorption of dose is associated with the transfer of energy: A. To electrons. B. To photons. C. Only in the photoelectric process. D. Only from incident photons.

T25.

Hounsfield numbers in aCT image are linearly related to the: A. Mass attenuation coefficient. B. Linear attenuation coefficient. C. Electron density of the patient. D. Number of photoelectric interactions per em.

T26.

With the exception of hydrogenous materials, for which interaction is the mass attenuation coefficient similar for most materials? A. Photoelectric B. Compton C. Pair production D. Photonuclear disintegration E. Nuclear scattering reactions

T27.

When a 10 keY photon undergoes a photoelectric interaction with a K-shell electron of binding energy 6 keV: A. A 6 ke V photoelectron is emitted. B. The photon is scattered with reduced energy. C. A characteristic x-ray is emitted. D. An electron-positron pair is created.

T28.

Suppose that a photon undergoes a Compton interaction in which the backscattered photon has the minimum energy. At what angle is the Compton electron emitted relative to the direction of the initial photon? A. Cannot be determined from the information given. B. 0° c. 90° D. 180° E. None of the above.

T29.

If the linear attenuation coefficient of a photon beam is 1.0 cm- 1, the half-value layer (HVL) is: A. 0.693 em B. 1.39 em C. 1.44 em D. Cannot calculate without knowing the energy of the beam.

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therapy questions TlO.

Collecting all the charge produced by a beam ofphotons in a small volume of air, under conditions of electronic equilibrium, is a direct measure of: A. Dose equivalent. B. LET. ( . Absorbed dose. D. Exposure. E. Specific ionization.

Tll.

The x-ray spectrum of a 10 MV linac has: A. Photons, all of which have an energy of 10 MY, ±5%. R. A maximum photon energy of 10 MeV and an average of about 3 MeV C. A maximum photon energy of30 MeV and an average of about 10 MeV D. Equal numbers of photons at all energies up to 20 MeV E. Prominent peaks at the characteristic x-ray energies of the target.

T32.

A superficial x-ray unit has an HVL of 2 mrnAl. Which ofthe following will cause the greatest increase in dose rate at the patient's surface? A. Increasing the filtration by 1 mm. B Increasing the beam current from 8 to 12 rnA. C. Changing the kVp from 100 to 80. D. Increasing the SSD from 15 to 18 em.

Tll.

The f factor is all of the following, except: A. Not defined above 3 MeV B. 0.876 cGy/R for 6°Co in air. C. Dependent on the composition of the medium and the photon energy. D. Greater for fat than for bone at 100 ke V

T34.

Apart from heat production, which of the following predominantly occurs when electrons of 150 kVp hit a tungsten anode? A. Compton scatter B Elastic scatter C. Bremstrahlung radiation D. Coherent scatter E. Photoelectric interaction "

TlS.

The depth of maximum dose for a photon beam is approximately equal to: A. The depth at which dose and kerma are equal. B. The maximum range of the secondary electrons. C. The depth at which electronic equilibrium occurs. D. All of the above. E. None of the above.

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therapy questions T36.

In order to convert exposure (R) to absorbed dose (mGy), the factor for diagnostic x-rays and muscle tissue by which exposure is multiplied is closest to A. 0. 1 B. 5

c.

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D. 20 E. 90

TJ 7.

Which A. B. C. D. E.

T38.

When a cylindrical chamber is used to measure percent depth dose for a megavoltage photon beam in a water phantom, the measured ionization curve should be shifted: A. Toward the phantom surface by about one-half of the chamber inner radius. B. Away from the phantom surface by about one-half of the chamber inner radius. C. By an amount dependent on the beam energy. D. Only for electron beams, but not for photon beams.

T39.

A parallel-plate chamber is used to measure the percent depth ionization of an electron beam in water. The measured percent depth ionization distribution: ' A. Equals the percent depth dose distribution. B. Equals the percent depth dose distribution only after the build-up region.

therapy unit would produce the highest beam energy: Gamma Knife® Linear accelerator TomoTherapy® CyberKnife® Proton Therapy

C. Needs to be multiplied by

("L/P)::rer to obtain the percent depth dose. water

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D. Needs to be multiplied by J1 p a1r. T40.

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to obtain the percent depth dose.

According to the AAPM TG-51 calibration protocol, all of the following are true, except: A. TG-51 applies for photon and electron beams with energies between Co-60 and 50 MeV. B. TG-51 provides a way to nteasure absorbed dose in water, in Gy, at the point of measurement of the ion chamber, when it is absent. C. Ionization chamber must have a calibration factor obtained in water, at an Accredited Dosimetry Calibration Laboratory (ADCL). D. Reference dosimetry must be performed in a phantom with dimensions of at least 30x30x30 em. E. Electron beams must be calibrated with chambers having an electron calibration factor provided by an Accredited Dosimetry Calibration Laboratory (ADCL).

Raphex 2010

therapy questions T 41.

Linear accelerators must have the TG-51 full calibration in a water tank for all photons and electrons beams in clinical use: A. Every month. B. Once a year. C. Monthly. D. Daily. E. Only at acceptance testing of a new linac, for all clinical beams.

T42.

In dose measurements using an ion chamber, the reading is corrected to the reading that would have been obtained at the standard temperature and pressure of: A. 32 °C, 730 mm Hg. B. 22 °C, 760 mm Hg. C. OK, lOOmmHg. D. 273 K, 101.33 kPa.

T43.

"Homogeneity index" is used to express: A. The degree of dose uniformity in the target volume. B. The degree of dose uniformity in organs at risk. C. The degree of CT number uniformity in a CT image. D. The degree of intensity uniformity in an intensity-modulated field.

T44.

The dose beyond 3.0 em dense bone in a 6 MV beam, compared to that calculated without a heterogeneity correction, would be about _ _ _ . A. 6% greater B 3% greater C. 3% less D. 6% less E. 12% less

T 45.

A spine field set up at 100 em SSD delivers 250 cGy at 5 em depth. The maximum tissue dose is cGy.

Data: Depth (em) PDD TMR 1.6 100.0 1.0 5.0 87.1 0.928 Output in tissue= 1.000 cGy/MU at 100 em SSD,