# Dosimetry: Final Exam

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 Author: RadiationTherapy ID: 247185 Filename: Dosimetry: Final Exam Updated: 2013-12-04 17:32:27 Tags: radiation therapy dosimetry treatment planning Folders: Description: Final Exam (Bentel) Show Answers:

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1. Name that fractionation:
Irradiating a patient twice daily with a smaller than normal daily dose, making it possible to deliver 15-20% more dose over the same period of time.
• Hyperfractionation
• (bid)
2. Name that fractionation:
Delivering the same dose over a shorter period of time.
• Accelerated Fractionation
3. When did Wilhelm Conrad Roentgen discover x-rays?
November 8, 1895
• Henri Becquerel
• 1896
5. What are the 3 most important factors in radiation protection?
describe the relationship of each to reduction in exposure
• Time (decrease exposure time)
• Distance (increase distance to source)
• Shielding (increase the amount of shielding)
6. What is the half-life of Cobalt-60
5.26 years
7. The gross palpable extent and location of malignant growth:
Gross Tumor Volume   (GTV)
8. The tissue volume that contains the GTV and subclinical microscopic malignant disease:
Clinical Target Volume    (CTV)
9. Contains the tumor and adjacent tissues:
• Planning Target Volume    (PTV)
• (always larger than the GTV)
10. To calculate the energy needed to treat along 90% isodose line for electrons multiply the depth by ______.
• 90% Isodose Line:
• 4

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

12. What is the formula used to calculate the MU for electrons?

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

13. What is the formula used to calculate the wedge angle?
14. 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
15. The energy of a photon beam divided by four will give you the depth of the beam's _______ in most cases.
Dmax

16. What does the RT (T) stand for?
17. The purpose of this machine is to duplicate the geometry & mechanical movements of radiation therapy machine, what is it?
a Simulator
18. 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)

19. 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)

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

22. 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)
23. A sheet of Lucite placed in the beam to reduce it's depth of Dmax is called a ___________.
Beam Spoiler
24. 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

SCEFDD: SSD, COLLIMATOR, ENERGY, FIELD SIZE, DEPTH, DENSITY
25. Radiation therapy units operating at approx 50-120 kVp are:
Superficial units
26. Orthovoltage units usually operate at ______ SSD.
50-70 cm SSD
27. Orthovoltage units usually operate in the energy range of :
150-500 kVp
28. LINACs produce high energy beams by accelerating CHARGED particles in a ___________
Linear tube
29. A collimator _____ the beam.
Defines
30. The photon beam from a LINAC is intercepted by:
Ionization chambers & a flattening filter
31. A flattening filter reduces the __________ in the center of the unfiltered beam
Dose Rate
32. The average energy of a Cobalt 60 beam is:
1.2 MeV
33. The half-life of Cobalt 60 is:
5.26 years
34. Dose rates ________ with increased field size & ________ with increased distance.
• INCREASE w/ increased field size
• DECREASE w/ increased distance
35. 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)
36. In a fixed SSD technique, the dose is usually normalized (or weighted) at ________.
at Dmax
37. In an isocentric technique, the dose is usually normalized (or weighted) at _________.
• at the Isocenter
• aka the Target center
38. In an electron beam, the _____ isodose curve bulges and the _____ isodose curve constricts.
20% bulges

90% constricts
39. 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
40. 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
41. 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
42. ☆The Abdomen is defined as the portion of the body that lies between the _______ & the ________ and that contains the __________.
• THORAX
• PELVIS
• PERITONEAL CAVITY
43. ☆Generally speaking, the kidney tolerance dose to irradiation in the adult is:
2000 cGy delivered at 180 to 200 cGy per fraction
44. ☆The most common site of pancreatic tumors is the ______ of the pancreas.
45. ☆Wilms' tumor is a tumor originating in the _______.
• Kidney
• (kiddie kidneys)
46. ☆Neuroblastoma is a tumor most often originating in the __________.
Sympathetic Nervous System

often arising in abdomen, chest or neck
47. ☆When pelvic irradiation is delivered in an obese patient in the supine position, the concern is that uncertainty of dose due to variations in patient _________ would be caused when attempts were made to eliminate skin folds.
uncertainty of DOSE due to variations in patient THICKNESS
48. ☆To reduce the volume of __________ within a pelvic field, the patient's position should be prone on a belly board.
Small Bowel
49. ☆The primary purpose of a testicular shield is to reduce the amount of _________ dose in the testes.
INTERNAL SCATTERED dose in the testes
50. ☆Of gynecological tumors treated with radiation therapy, the most common type is:
Squamous cell carcinoma of the Cervix
51. ☆The depth of the deep inguinal nodes can vary from _____ to _____cm depending on the patient's size.
2-18 cm
52. The dose under a 5-HVT kidney block is approximately ______ to ______% of the dose delivered at mid-depth on the central axis.
10-20%
53. When a three field technique (anterior and lateral opposed fields) is used in the treatment of pancreatic tumors, the best dose distribution is achieved with wedge(s) in the ________ field(s) and more weighting on the ________ field(s).
• wedges in the LATERAL fields
• more weighting on the ANTERIOR field
54. How much of the kidney should be excluded from the treatment field in order to preserve proper function?
2/3 of the kidney must be excluded
55. When patients with advanced cervical carcinoma are treated, the majority is delivered via ________.
56. Insertion of a 1-HVT block in both fields during the entire course of treatment would deliver approx ______ of the dose in the shielded organs and the dose distribution under the shields would be similar to that of using ______ shields only during a portion of the treatment.
• 50%
• 5-HVT
57. What are the three methods of kidney blocking?
• 1. Fully blocking the kidneys once tolerance dose is reached
• 2. Blocks that allow partial transmission of the beam for the entire treatment course
• 3. Fully shielding from one field only
58. ☆The 10-year survival for patients with all stages of Hodgkin's disease is approximately:
80%
59. ☆The patient position for treatment of a mantle field in Hodgkin's disease is usually supine with the ________ extended and the arms __________.
• CHIN extended
• arm RAISED ABOVE THE HEAD
60. ☆It is always important to align the patient with the ________ laser every day because if it is not, the field is rotated with respect to the patient's body.
Sagittal
61. ☆Tattoos made in the patient's skin indicating irradiated areas can shift due to _______ and ________.
• Growth
• Weight changes
62. ☆The advantages of ________ therapy are that it provides superior normal-tissue sparing and improved precision.
63. ☆High- and low- dose total body irradiation is used in the preparation for a _________ and in the treatment of ____________.
• BONE MARROW TRANSPLANT (preparation)
• total dose: 900-1200 cGy

• CHRONIC LYMPHOCYTIC LEUKEMIA (treatment)
• total dose: 100-400 cGy
64. ☆The most common position for patients receiving total-skin electron irradiation is ___________.
Standing with legs spread & arms raised
65. ☆The main goal of radiation therapy in patients with bone metastasis is to prevent ________ and reduce _________.
• prevent FRACTURES
• reduce PAIN
66. ☆In patients treated for a spinal cord compression, the treatment field should include approximately two ____________ in each direction beyond demonstrable disease.
approx TWO VERTEBRAL BODIES in each direction beyond demonstrable disease
67. What is the average depth of the spinal cord?
4 to 6 cm
68. The average dose and fractionation schedule for multifocal brain metastasis treatment is _____ cGy in ____ week
or
_____ cGy in ____ weeks
• 2000 cGy in 1 week
• or
• *3000 cGy in 2 weeks*
69. A typical treatment regimen of the cervix would include:
• 40-50Gy via a four field box
• ⇨ Cone down with midline block (MLB)
70. DICOM (Digital Imaging and Communications in Medicine)  is an established standard format for the use and exchange of medical ________, media and ________ across a computer network. (a LAN or a WAN)
DICOM (Digital Imaging and Communications in Medicine) is an established standard format for the use and exchange of medical DATA, media and IMAGES across a computer network. (a LAN or a WAN)
71. Where is Point A located?
• 2cm superior of the external cervical os
• and
• 2cm lateral to the uterine tandem
72. An off axis point is any point not on the ____________. The off axis point is used as a __________ point to tell the Dr what the dosage and effect on the tissue at that point will be as well as to find the __________.
• any point not on the CENTRAL AXIS
• CALCULATION point
• Off Axis Ratio (OAR)

often used w/ hodgkin's mantle fields
73. The iliac crest is at the level of ______ in the spine.
L-4
74. A _______________ is a computer generated 2D radiograph displaying skeletal anatomy rendered from a three dimensional data set, such as CT or MRI.
75. What is the most common intracranial tumor?
Metastatic disease from a primary tumor elsewhere in the body
15%
77. What is make-up of Cerrobend?

(percentage of each material)
• BLT with Cheese
• Bismuth: 50%
• Tin: 13.3%
78. Secondary scatter in the metal-tissue interface can cause high dose in the adjacent tissues but can be reduced by placing ___________ over the teeth.
2 to 4 mm of tissue-equivalent material
79. When a lip lesion is treated, it is possible to reduce the mucosal reaction by placing an internal shield _______ to the tumor and covering the shield with ________.
DISTAL to the tumor

WAX
80. If a 30° wedge is left out of the treatment during two of five treatments, the central axis dose is ________ (increased/decreased) and the isodose distribution ______ (is/is not)  affected.
• central axis does is INCREASED
• isodose distribution IS affected
81. Treatment fields should be labeled in the chart with reference to:
(2)
• 1. Anatomic description
• 2. Unique number assigned to each field
82. The most commonly used beam energy to treat head & neck cancer is:
• Cobalt 60
• 4 MV photons
• 6 MV photons
83. The majority of cancer in the head & neck region is:
Squamous cell carcinoma
84. Xerostomia is caused by irradiation of the
Salivary Glands
85. In the treatment of head & neck cancer, immobilization is particularly important because of:
(2)
• 1. proximity of several radiosensitive organs
• 2. small tumor margins
86. Retinoblastoma is a tumor of the eye that usually occurs in:
(what age group?)
Small children

(weeks to months old)
87. Parotid tumors are often treated using:
(what type of energy)
Mixed ELECTRONS & PHOTON beams
88. What is a common treatment technique of pituitary lesions?
A three field technique (vertex & opposed wedged laterals)
89. The disadvantages of a vertex field is that it often exits in the _________ and the ___________.
exits in the PHARYNX & SPINAL CORD

90. In a typical CSI setup, to avoid having the caudal margin of the lateral brain fields diverge into the cephalad aspect of the posterior spinal field, the foot of the couch is turned:
in TOWARD the collimator

CSI: table kicked In towards the gantry
91. Of all childhood brain tumors, medulloblastoma represents about ______%
20%
92. The most commonly occurring cancer in the US is ________ cancer.
LUNG cancer
93. A lung boost is often delivered via:
Opposed Oblique Fields
94. Tumors in the lower two-thirds of the esophagus can be boosted via a _______ and two _________ oblique fields.
Anterior & two Posterior oblique fields
95. The number of US women who will develop breast cancer is approximately:
1/10
96. The regional lymph nodes in breast cancer are the:
(3)
• Internal Mammary LN
• Supraclavicular LN
• Axillary LN
97. To avoid beam divergence from the tangential fields into the supraclavicular field, the foot of the couch is turned (kicked) ________ from the collimator/gantry.
AWAY from the gantry

kick table Away from the gantry for tAngents
98. To avoid beam divergence into the lung by the tangential fields, the central axes of the tangential fields can be separated by slightly more than ______ until the deep margins become _________.
180°

Parallel
99. The most important considerations to avoid radiation-induced pneumonitis are:
(3)
• 1. Total Dose
• 2. Fractionation schedule
• 3. Volume of irradiated lung

DFV = Dose, Fractionation, Volume
100. What is the most common type of glioma?
Astrocytoma

(side note: 50-60 Gy)
101. What is the origin of gliomas?
Glial cells
102. What is the formula used to determine how many degrees the table will need to be kicked?
Tan theta

Tan θ =
103. What are the 3 traditional whole brain set-ups?
• 1. Classic/Traditional borders with some collimation, not to include C-1
• 2. Includes C-1 by angling or turning the collimator
• 3. German Helmet- includes while head with blocks over the eyes, no collimator angling, C-1 not included
104. What are the borders of a generic whole brain set-up?
• 1. Orbital Ridge
• 2. EAM or Tragus
• 3. Base of Skull

1-2 cm of flash on all sides
105. Craniospinal fields are often used to treat:
(2)
Medulloblastomas

Primitive Neuroectodermal Tumors
106. Other than transverse myelitis, name another radiation induced spinal injury:
Lhermitte's Sign
107. The gantry angles for tangent fields are usually separated by _______°.
185-186°
108. When treating the supraclavicular LN of a breast cancer patient, the gantry is angled _____° away from the side of the cancer.
15° away
109. A ________ is a plot of target or normal structure volume as a function of dose.
Represents the amount of dose (an absolute value) received by a percentage or fraction of a structure like an organ (a relative value)
Dose Volume Histogram  (DVH)
110. What are the 3 classic phases of lung cancer treatment?
1. AP/PA fields ⇨ 45Gy

2. Offcord Boost ⇒ 20Gy

• 3. Primary lesion boost → 10Gy
• (often via AP/PA)
111. Name that fractionation:
Irradiating a patient twice daily with a smaller than normal daily dose, making it possible to deliver 15-20% more dose over the same period of time.
• Hyperfractionation
• (bid)
112. Name that fractionation:
Delivering the same dose over a shorter period of time.
• Accelerated Fractionation
113. What are the two most important factors for immobilization with head & neck cancer?
Comfort & Reproducibility
114. The average depth of lymph nodes is ______ to ______ cm.
1-3 cm
115. The tissue to air ratio (TAR) at Dmax is also known as the _________.
Back scatter factor (BSF)

BSF = TAR@Dmax
116. Identify & describe each whole brain set-up (including borders)
• A. Classic or traditional whole brain w/o C1 included (borders: orbital ridge, tragus or EAM, base of skull 1-2cm w/ flash)
• B. Whole brain w/ C1 included by adjusting collimator
• C. German Helmet field includes whole head with a block over the eyes; no collimation; C1 not included
117. The _______ is defined as the ratio of dose at a specified point in tissue (or in a phantom) to the dose at the same distance in the beam at a reference depth, usually 5 cm.
Tissue Phantom Ratio (TPR)

118. When using a SCV field to treat breast cancer the gantry is angled 15° to avoid inclusion of the:
(3)
• trachea
• esophagus
• spinal cord

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