Radiation Therapy Physics Mid-Term Review – Flashcards
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The smallest unit of an element that retains all its chemical properties & characteristics
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Atom
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Components of a Thoreaus filter, from the tube to the patient
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Tin, Copper, Aluminum
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The _________ or _______ is the number of PROTONS in the nucleus
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Atomic Number; 'Z'
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The _________ or _______ is the number of protons and NEUTRONS in the nucleus
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Atomic Mass Number; 'A'
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The most important method of producing X-rays in therapy units
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Bremsstrahlung Interactions
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At higher energies, photons are emitted from the target in the SAME direction as the incident electrons, this is called
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Forward Peaking
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The energy of an electron at rest is equal to
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0.511 MeV
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The kinetic energy acquired by an electron in passing through a potential difference of 1V is the definition of the
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Electron Volt (eV)
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According to the formula 2n2 what is the maximum number od electrons the O shell can contain
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50
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Which of the following properties may define electromagnetic radiations
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Frequency - Wavelength - Energy
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What is the average energy of a 15 MeV photon beam
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5 MeV
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For diagnostic X-ray tubes, X-rays are emitted in all directions; therefore a ________ target is used
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Reflectance
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In the formula E=hv the 'v' is
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Frequency
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As wavelength decreases the frequency increases the energy of a photon
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Increases
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Removal or addition of one or more electrons from an atom is
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Ionization
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Which of the following are characteristic of a photon
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No Mass - No Charge - Speed of Light
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A high LET radiation will cause more biological effects on tissue than a low LET radiation
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True
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Wavelength can be measured in
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Nanometers & Angstroms
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Frequency is measured in
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Cycles Per Second & Hertz
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1 MeV is equal to
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1,000,000 eV
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A linear accelerator uses a ________ target
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Transmission
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Removal of weaker energy x-rays from a beam is called ________
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Hardening
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An ________ collision is an interaction where kinetic energy is lost
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Inelastic
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____ Curie = 3.7x10^10Bq
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T
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____ Seivert = 2000 Rem
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20
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5 rem = _____ mrem
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5000
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______ radiation occurs when an electron slows down or changes direction as it approaches the nucleus
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Bremsstrahlung
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The energy of a characteristics photon depends on _________________
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Difference in e- shell binding energy
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Bremsstrahlung production is a (radiative or collision) interaction
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Radiative
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The energy of a bremsstrahlung photon depends on
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Proximatey to the nucleus
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Ortho-voltage x-rays are in the range of ______ kVp
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150 - 400
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Traditional unit of x-ray
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Curie
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SI unit of radioactivity
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Bacquerel
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Traditional unit of radiation exposure
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Roentgen
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Traditional unit of radiation absorbed dose
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Rad
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SI unit of radiation absorbed dose
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Gray
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Traditional unit of radiation dose equivalent
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Rem
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SI unit of radiation dose equivalent
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Sievert
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Atoms with the same number of protons, different number of neutrons
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Isotopes
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Total amount of energy that it takes to hold a nucleus together
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Nuclear Binding Energy
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Minimum amount of energy needed to keep the atom together
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Ground State
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Emission of energy in the form of electromagnetic radiations or energetic particles
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Radioactivity
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Atoms with the same mass number; different proportions of photons and neutrons
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Isobars
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Emission of matter or energy
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Radiation
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Atoms with the same number of neutrons; different number of protons
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Isotones
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SI unit of radiation exposure
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Coulomb/Kilogram
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According to the inverse square law, if you double the distance
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Intensity is one-fourth of the original intensity
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Beam-shielding blocks are usually how many thick
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5
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The most important interactions in radiation therapy are
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Compton effect & Pair Production
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The interactions that occur above 10 MeV are
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Photodisintegration & Pair Production
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The HVL for megavoltage beams is measured in
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mm Pb
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The higher the photon energy, the less likely that this interaction will occur
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Photoelectric Effect
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In this interaction, a photon interacts with a loosely bound outer shell electron
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Compton Effect
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In a treatment room, secondary barriers are needed to protect from
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Scatter radiation
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These two interactions degrade the radiographic image on a diagnostic film
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Compton Effect & Coherent Scatter
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In photodisintegration, neutrons are produced inside the patient's body
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False
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In the Compton effect, the maximum energy of a 90 degree scattered photon is
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.511 MeV
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The photoelectric effect is more likely to occur in bone than in soft tissue
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True
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Results in the formation of a positron and negatron of .511 MeV each
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Pair Production
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Energy is both absorbed and scattered
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Compton Effect
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Important in designing blocks and room shielding
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Compton Effect
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No ionization occurs
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Coherent Scatter
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Impossible below 1.02 MeV
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Pair Production
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Important in the range of 1 MeV or higher
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Pair Production
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Results in the production of neutrons
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Photodisintegration
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Depends on the electron density of the material
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Compton Effect
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Also called incoherent effect
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Compton Effect
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More likely in high Z materials
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Photoelectric Effect
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Of no importance in megavoltage therapy
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Coherent Scatter
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Incoming high-energy photons strike the nucleus of an atom
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Photodisintegration
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Can lead to an annihilation reaction
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Pair Production
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What is the linear attenuation coefficient in a beam with a HVL of 2 mm Cu
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.346 mm^-1
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A low intensity beam can have photons of very high energies
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True
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In radiation therapy, when calculating the probability of radiation interacting with materials of various densities, such as lead, soft tissue, and bone, the ______ is usually used
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Mass Attenuation Coefficient
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The equivalent energy of a 6 MV photon beam is
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2
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Probability per unit thickness that any one photon will be attenuated
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Linear Attenuation Coefficient
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Removal of energy from the beam
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Attenuation
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Type of scatter that travels 180 degrees from where the incident photon hit the atom
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Backscatter
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A loosely bound outer shell electron
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Free Electron
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Antiparticle that annihilates a free electron in pair production
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Positron
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Ratio of beam intensity after filtration to beam intensity
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Transmission
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An electron that is ejected instead of a photon in the photoelectric effect
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Auger Electron
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The number of photons per square centimeter
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Intensity
