Dosimetry Test 1

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Dosimetry Test 1
2013-11-21 20:49:39
radiation therapy dosimetry treatment planning

Dosimetry and Treatment Planning Ch 1, 2, 3, 6, 7 (Bentel) Test 9/23
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  1. When did Wilhelm Conrad Roentgen discover x-rays?
    November 8, 1895
  2. Who discovered radioactivity?
    • Henri Becquerel
    • 1896
  3. Who discovered radium & polonium? When?
    • Marie & Pierre Curie
    • 7/1898 Po
    • 12/1898 Ra
  4. Artificial radioactivity was discovered in ______ by __________
    • 1934
    • Irene Curie & Frederic Joliot
  5. Dose fractionating to achieve the same tumor response with less injury to normal tissue was discovered by
    Henri Coutard & Claude Regaud
  6. The first therapeutic use of x-rays was on _________.
    • January 28, 1896
    • (breast cancer)
  7. What is the half-life of Cobalt-60
    5.26 years
  8. The gross palpable extent and location of malignant growth:
    Gross Tumor Volume   (GTV)
  9. The tissue volume that contains the GTV and subclinical microscopic malignant disease:
    Clinical Target Volume    (CTV)
  10. Contains the tumor and adjacent tissues:
    • Planning Target Volume    (PTV)
    • (always larger than the GTV)
  11. The dose at a point that has been "forced" to 100%
    Dose Nomalization
  12. What are the limitations of isodose curves?
    • 1. Only depict the dose from a SINGLE BEAM
    • 2. Represent dose distribution in ONE PLANE
    • 3. Only for SQUARE or RECTANGULAR fields
  13. The region in which the dose gradually increases until it reaches a certain depth and then falls off due to the increasing thickness:
    the Buildup Region
  14. What is the major factor in determining the depth (dmax) at which dose maximum occurs?
    Beam energy
  15. When a photon beam encounters a surface obliquely, Dmax moves _________ to the surface.
  16. For electron beams, the Dmax and actual dose on the skin surface ________ with beam energy. 
    (increase or decrease)
    Increase with beam energy
  17. To calculate the energy needed to treat along 90% isodose line for electrons multiply the depth by ______.
    • 90% Isodose Line:
    • 4

  18. To calculate the energy needed to treat along 80% isodose line for electrons multiply the depth by ______.
    • 80% Isodose Line:
    • 3

  19. The angle separating the two central axes:
    • Hinge Angle
  20. SSD + depth =
    SAD Source to Axis Distance
  21. TFD or FFD
    • Target to Film Distance
    • or
    • Film to Focal Distance
  22. EPI
    Electronic Portal Imaging
  23. What is the formula used to calculate the MU for electrons?

    • %Pxd: percentage prescription dose
    • ecutout factor: 1
    • ie: dose 200cGy/fx  w/ 90%

  24. What is the formula used to calculate the wedge angle?
  25. Rule of Thumb:

    When in doubt when calculating energy to for an electron treatment the energy (MeV) should be ____ the maximum depth of the tumor.
    The energy (MeV) should be 3X the maximum depth of the tumor.

    ie: a 3cm depth = a 9MeV beam
  26. The energy of a photon beam divided by four will give you the depth of the beam's _______ in most cases.

  27. What does the RT (T) stand for?
    Registered Technologist in Radiation Therapy
  28. The first linear accelerator was developed by ____________ in ______.
    Wilderoe in 1928

    (to accelerate heavy ions)
  29. The purpose of this machine is to duplicate the geometry & mechanical movements of radiation therapy machine, what is it?
    a Simulator
  30. What are the three primary methods of dose determination in a radiation therapy department?
    • Ionization Chamber
    • TLD's
    • Photographic Film
  31. The ________ expresses the penetration and the quality or hardness of a beam.
    Half Value Thickness  (HVT)
  32. The thickness of a material that reduces the intensity of the beam to half of its original value:
    Half Value Thickness  (HVT)
  33. What is the ratio of the absorbed dose at a given depth to the absorbed dose at a fixed reference point, usually Dmax ?
    Percentage Depth Dose  (PDD) or (%DD)

  34. What is the ratio of the absorbed dose at a given depth in tissue to the dose at the same point when it is at Dmax ?
    Tissue Maximum Ratio  (TMR)

  35. The region near the edge of the field margin where the dose falls rapidly:
  36. The angle through which an isodose curve is tilted at the central axis of the beam at a specified depth.
    Wedge angle

  37. What is the correction factor of the lung?
  38. When a tumor is not situated at mid-depth, it can be beneficial to deliver a higher dose from the field where the tumor is shallower by ________ the beams.
  39. The wedge angle needed depends on the:
    Hinge angle  
  40. What is the formula used to find the necessary gap size?

    • if not otherwise specified, assume SSD is 100cm
  41. Define:
    • Back Scatter Factor (BSF)                                   The ratio of dose on the central axis at Dmax to the dose at the same point in air.
    • *independent of SSD
    • *depends on energy & field size
  42. Dose rates _________ with field size.
    (increase or decrease)
  43. What is the ratio of the dose rate of a given field size to the dose rate of the reference field size?
    Output Factor (OF)
  44. The intersection of the horizontal and vertical axes of rotation is referred to as the ___________.
  45. The _____ axis represents the patient's left-to-right direction.
    X axis

    • +x indicates the patient's right
    • -x indicates the patient's left
  46. The ______ axis represents the cephalad-to-caudal direction.
    Y axis

    • +y cephalad (cranial)
    • -y caudal
  47. The _____ axis represents the anterior-to-posterior direction.
    Z axis

    • +z anterior
    • -z posterior
  48. What is the name of a tissue equivalent material used to eliminate the skin sparing effect?

    Superflab most common type
  49. Tissue-equivalent materials used in megavoltage radiation therapy to reduce the depth of the Dmax is called:

    eliminates the skin sparing effect
  50. A sheet of Lucite placed in the beam to reduce it's depth of Dmax is called a ___________.
    Beam Spoiler
  51. What energy range does a conventional simulator operate in?
    kV range

    (photoelectric effect)
  52. The dose delivered to a patient is dependent upon these six factors:
    • 1. Depth of calculation point below the surface
    • 2. Energy of the beam (penetrating power)
    • 3. Density of tissue
    • 4. SSD
    • 5. Field Size (FS)
    • 6. Collimator Design

  53. What was the only measure of exposure for the early pioneers of xrt
    The erythema dose
  54. The Manchester system of radium distribution was developed by:
    Ralston Paterson & Herbert Parker

    Manchester = Paterson & Parker
  55. The pentrometer to measure the quality of x-rays was introduced by:
  56. The Roentgen was internationally accepted as a unit of measure for x-rays and gamma rays in:
    • Roentgen
    • 1928
  57. The rad as a unit of absorbed dose was recommended by the ICRU in:
    • rad
    • 1953
  58. The use of betatrons in XRT became unpopular because:
    Betatrons produce low dose rates & have limited field sizes
  59. Radiation therapy units operating at approx 50-120 kVp are:
    Superficial units
  60. Insertion pf aluminum, copper & tin filter into the x-ray beam causes ________ to be absorbed
    Low energy x-rays
  61. Orthovoltage units usually operate at:
    50-70 cm SSD
  62. Orthovoltage units usually operate in the energy range of :
    150-500 kVp
  63. Orthovoltage beams are generally _______ penetrating than superficial beams
  64. LINACs were first developed:
    following WWII
  65. LINACs produce high energy beams by accelerating CHARGED particles in a ___________
    Linear tube
  66. Because electrons scatter readily in air ________ extending close to the patient's skin are used
  67. A collimator _____ the beam.
  68. The photon beam from a LINAC is intercepted by:
    Ionization chambers & a flattening filter
  69. A flattening filter reduces the __________ in the center of the unfiltered beam
    Dose Rate
  70. The first Co-60 machine was introduced in:
    the 1950's
  71. The average energy of a Cobalt 60 beam is:
    1.2 MeV
  72. The half-life of Cobalt 60 is:
    5.26 years
  73. The penumbra of a LINAC is ______ than that of a Cobalt 60 machine
  74. The point around which the source of the beam rotates
    The isocenter
  75. The secondary collimators are largely responsible for the _________ of the beam edges
  76. Simulators are primarily used to:
    Duplicate the geometry of therapy machines
  77. A HVT is a way of expressing the _______ of a beam.
    QUALITY of a beam
  78. Dose rates in air express:
    Dose without a phantom & with a build-up cap at a given distance
  79. Dose rates ________ with increased field size & ________ with increased distance.
    • INCREASE w/ increased field size 
    • DECREASE w/ increased distance
  80. Increasing the distance from 80 to 90 cm causes the dose rate to change by:
    • 0.7901
    • Use the Inverse Square Factor to solve:

    • so,
  81. Percentage depth dose is dependent on:
    • Field size
    • Energy
    • Distance

    PDD needs the FED
  82. The TAR at 5 cm depth for a 10x10 field minus the TAR at 5 cm depth for a 0x0 field gives the:
    Scatter Air Ratio (SAR)
  83. The width of penumbra increases with:
    Increased SSD & Source Size

    Decreased Source-collimator distance
  84. In a fixed SSD technique, the dose is usually normalized: 
    at Dmax
  85. In an isocentric technique, the dose is usually normalized:
    at the Isocenter
  86. In a typical electron beam, only the ______ to ______ isodose lines bulge out in the penumbra region, causing great difficulties in matching adjacent electron fields uniformly
    10% to 50%
  87. Photon isodose curves used in dose calculations on a patient usually require corrections for:
    Oblique incidence & surface irregularities
  88. Electron isodose curves used in dose calculations on a patient usually require corrections for:
    Beam obliquity & Surface irregularities
  89. The depth of Dmax for any photon beam energy is reduced by:
    • Larger field size &
    • Oblique incidence
  90. Treatment fields should always be shaped so that the beam edge:
    Crosses perpendicular to the spinal cord
  91. In port films of parallel opposed isocentric fields of a lung tumor, the _________ field will appear to include a longer segment of the spinal cord than in the _________ field.
    • Anterior
    • Posterior
  92. To minimize the gap between two adjacent fields a ___________ can be used.
    Half-beam block
  93. When adjacent areas must be treated, it is best to calculate the _____ necessary between fields to prevent overlap.

  94. When an isodose curve of about 22° is needed, isodose charts for an ______ and a _____ are used.
    an Open field & a 45° wedge angle
  95. In an electron beam, the _____ isodose curve bulges and the _____ isodose curve constricts.
    20% bulges

    90% constricts
  96. When parallel opposed 6 mV photon beams are used in a 20 cm thick patient, the maximum dose will occur at:
    The entrance & exit of each field
  97. When a 4 mV and a 15 mV photon beam are used to treat parallel opposed fields in a 20 cm thick patient, the dose in the entrance/exit region is highest when the _____ beams are used.
    4 mV
  98. When a sector is skipped in an arc technique, the high dose area is shifted away from the __________.
    skipped sector
  99. When parallel opposed fields are used with the isocenter at mid-depth & one field is weighted twice as much as the other, the maximum dose is in the:
    Entrance/exit region of the field with the HIGHER weight.
  100. To minimize the risk of hot or cold spots in the junction between photon fields, the gap should be:
    Moved several times during the course of treatment
  101. Matching of electron beams on a chest wall is more difficult because some isodose curves _______ and others ______.
    • Bulge out 
    • Constrict
  102. The angle of beam divergence is ________ farther from the central axis
  103. When parallel opposed fields are used & the isocenter is at mid-depth in the chest, the length of the spinal cord is:
    Longer in the anterior field than in the posterior
  104. The three planes in a patient are across the body, along the body in a lateral view & along the body in an anterior view. Respectfully, these are referred to as:
    Axial- across the body

    Sagittal- along the body in a lateral view

    Coronal-along the body in an anterior view
  105. When a patient is re-aligned with a laser alignment system, it is necessary to align:
    two points separated by distance
  106. Treatment planning CT's are different diagnostic CT's because:
    In a treatment planning CT the patient must be in the treatment position on a flat surface
  107. The anterior & posterior skin surfaces seen on a lateral radiograph of a patient's pelvis does not represent the patient's:
    skin surface in midline
  108. Discrepancies in the patient/beam alignment between the first port film & the simulation film may be due to:
    • Differences in laser alignment systems
    • Different couch tops
    • Differences in clothing under the patient
  109. When the location of a contrast-filled bladder is transported from a set of orthogonal films to a transverse contour of the pelvis, the _______ film yields info in the right/left & cephalad/caudal directions while the ______ film yields info in the ant/post & cephalad/caudal directions
    ANTERIOR: rt/lt  sup/inf

    LATERAL: ant/pos  sup/inf
  110. Uncertainties associated with delivering XRT can be totally avoided by:
    No special means, as there is no way to do so
  111. When the treatment fields are designed by the RadOnc, margins are always added around a tumor to account for:
    • Uncertainties in determining tumor extent
    • Penumbra
    • Patient motion