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Procedures: 2. DOSI/Treatment Volume Localization > CT Simulation > Flashcards

CT Simulation Flashcards

1
Q

what is the most common imaging modality used for radiation therapy treatment planning?

A

computed tomography (CT)

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2
Q

how are CT images produced?

hint - don’t overthink. Literally think what you sit at and see when doing a CT

A

by using an x-ray, detectors, and computer

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3
Q

T/F:

computed tomography CT is axial or spiral/helical

A

TRUE

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4
Q

what does it mean that computed tomography CT is axial spiral/helical?

A

just means the couch moves as the x-ray tube rotates within the gantry

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5
Q

what unit measures beam quantity?

A

Milliamperage (mA)

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6
Q

what does “beam quantity” mean?

hint - literally QUANTITY

A

how many x-rays are produced

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7
Q

an increase in mA leads to what?

A

an increase in patient dose

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8
Q

what is the CT tube current measured in?

A

coulomb/sec

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9
Q

slice ______ and the ____ between slices are key factors for generating high-quality digitally reconstructed radiographs (DRRs)

A

slice thickness, and
space between the slices

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10
Q

what does DRR stand for?

A

Digitally Reconstructed Radiographs

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11
Q

what should spacing be BETWEEN slices for CT?

hint - lower than __

A

lower than 5mm

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12
Q

what should slice thickness typically be set to for CT?

hint –> __ - __

A

2-3 mm

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13
Q

Imaging Terminology -

the following describes what?
“the diameter of the area being scanned”

A

FOV (Field of View)

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14
Q

Imaging Terminology -

the following describes what?
“area of interest to be scanned”

A

Scan field of view *our scouts

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15
Q

Imaging Terminology -

the following describes what?
“the number of shades of gray displayed on an image or the contrast of the image”

A

Window width (WW)

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16
Q

Imaging Terminology -

the following describes what?
“the MEDIAN shade of gray or HU (Hounsfield unit) WITHIN THE window width”

A

Window level (WL)

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17
Q

a narrow Window Width on a CT would have MORE or LESS contrast?

A

MORE

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18
Q

what Imaging Terminology changes the image brightness?

A

window level

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19
Q

an INCREASE in window level creates a BRIGHTER or DARKER image?

A

Darker image

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20
Q

a DECREASE in window level creates a BRIGHTER or DARKER image?

A

Brighter image

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21
Q

Imaging Terminology -

the following describes what?
“a value that represents a shade of gray, also known as the HU (Hounsfield unit)”

A

CT number

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22
Q

CT number can also be called a ___________

A

Hounsfield unit (HU)

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23
Q

what do CT numbers represent?

A

the density of different tissues (electron density)

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24
Q

what do CT numbers range from?

hint - negative number to positive number

A

-1000 to +1000

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25
Q

what does CT number -1000 represent?

A

air

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26
Q

what does CT number +1000 represent?

A

bone

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27
Q

what does CT number 0 represent?

A

water

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28
Q

Imaging Terminology -

the following describes what?
“the computer uses algorithms to create the CT image in different planes”

A

Reconstruction

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29
Q

what views (2) are reconstructed from axial slices?

A

Coronal and Sagittal

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30
Q

Coronal and Sagittal views are constructed from ___ slices

A

axial

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31
Q

the following is of what body plane?

A

axial/transverse

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32
Q

the following is of what body plane?

A

coronal

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33
Q

the following is of what body plane?

A

sagittal

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34
Q

_______ look like plain 2D radiographs and are reconstructed from the CT slices to show a beam’s-eye-view

A

DRRs (digitally reconstructed radiographs)

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35
Q

what does BEV stand for?

A

Beam’s Eye View

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36
Q

DRRs are made to compare to what?

A

compare to portal images (ports)

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37
Q

a ________ is a 3D image taken in the treatment position that provides data of the anatomy of the patient, such as the skin, tumor, and other organs within the body

A

contour

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38
Q

a ________ is a representation of the patient and is necessary for creating accurate treatment plans and calculating doses

A

contour

39
Q

T/F:
Target volumes, critical structures, and other anatomy are defined on the CT, MRI, and/or PET images

A

TRUE

40
Q

T/F:
Multiple studies from different imaging modalities can be fused together to give even more information to those planning the treatments (ie. dosimetry)

A

TRUE

41
Q

it is common to fuse ___ images and ____ images together

A

MRI and CT

42
Q

MRI scans are useful to show Hard OR Soft tissues

A

soft

43
Q

MRI and CT scans are commonly fused together to better highlight what anatomy?

A

prostate

44
Q

_____ scans are useful because they show the activity of the tumor

A

PET

45
Q

____ scans and ____ scans are commonly fused together to show areas of activity in sites such as the lung, and head and neck.

A

PET and CT

46
Q

what are the two different ways to plan a treatment once all the data is gathered? ________ planning and _______ planning

A

inverse planning
forward planning

47
Q

Which planning is being described below? - Forward or Inverse

  1. the planner chooses the energy, appropriate dose to the tumor, and the tolerances of the normal healthy tissues
  2. the computer then creates a plan using MLC pattern, shapes, directions, etc.
  3. used in IMRT (Intensity-Modulated Radiation Therapy)
A

Inverse planning

48
Q

Which planning is being described below? - Forward or Inverse

  1. the planner chooses the energy, number, shape, and direction of the radiation beams
  2. the computer calculates the isodose lines, and the planner must assess the dose distribution and make changes if necessary
A

Forward planning

49
Q

what ways can images be transmitted and stored? (3)
____ tapes
____ disks
____ network

A

magnetic tapes
optical disks
electronic network

50
Q

what does DICOM stand for?

A

Digital Imaging and Communication in Medicine

51
Q

what system creates the standard format to transfer images from imaging computers to the treatment planning computer?

A

DICOM (Digital Imaging and Communication in Medicine)

52
Q

what does PACS stand for?

A

Picture Archiving and Communication System

53
Q

what system is used to store and share images electronically?

A

PACS (Picture Archiving and Communication System)

54
Q

_____ are used to mark the patient in three areas to be able to triangulate and position the patient in a reproducible position for daily treatments

A

lasers

55
Q

lasers are used to mark the patient in ______ areas to be able to triangulate and position the patient in a reproducible position for daily treatments

A

three

56
Q

within treatment and simulation rooms, lasers are located ______, ______, and _______ on the ceiling in the ____, ____, and ____ coordinates

A

laterally, sagittally, and overhead

X, Y, and Z

57
Q

label the coordinates
1.
2.
3.

A

1 - Z
2 - Y
3 - X

58
Q

one CT slice dose @ skin is equal to ___ to ___ cGy (or __-___ mSv)

A

1-6 cGy

2-10 mSv

59
Q

CT sim terminology

define “Pixel”

A

picture element; each cell on the image matrix; 2D representation of tissues

60
Q

CT sim terminology

define “Voxel”

A

volume of element; contraction for volume element, which is the basic unit of CT or MR reconstruction

61
Q

“each cell on the image matrix; 2D representation of tissues” is describing what CT terminology?

A

PIXEL

62
Q

“volume of element; contraction for volume element, which is the basic unit of CT or MR reconstruction” is describing what CT terminology?

A

VOXEL

63
Q

CT sim

bone attenuation happens through ______ & _______ scattering

A

Photoelectric effect and
Compton scattering

64
Q

with a CT number of +1000, ____ appears ____ on a CT due to it’s higher density

A

bone appears white

65
Q

with a CT number of -1000, ____ appears ____ on a CT due to it’s low density

A

air appears black/dark

66
Q

what is white?
-orange?
-blue?

A

Z = white
X = orange
Y = blue

67
Q

which lasers move -
CT room or TRT room lasers?

which lasers are stationary (ie. do not move)

A

CT lasers can move

TRT room lasers do not move

68
Q

Total Target Dose is the ____ dose

A

absorbed dose

69
Q

Total dose is dependent on _____ and _____

A

location of the tumor and organs at risk

70
Q

what is a typical Curative dose?

A

180-200 cGy daily fraction
for a total of 5400-6000 cGy

71
Q

what is a typical Palliative dose?

A

300 cGy daily fraction
for a total dose of 3000 cGy

72
Q

describe Boost/Cone-down

A

a smaller field that can give a higher dose

73
Q

absorbed dose is measured in what?

A

normally measured in Gy (Gray)

74
Q

100 rads = ___ Gy

A

1 Gy

75
Q

what is the most common fractionation schedule?

A

once a day –> for 5 days –> for several weeks

76
Q

number of fractions vary with the _____ _____ dose

A

total tumor dose

77
Q

BID means what?

A

twice per day

78
Q

what is the MINIMUM amount of hours you HAVE to wait between BID trts?

A

MINIMUM 6 hours

79
Q

beam energy is dependent on the ______ of the patient and the ______ of the tumor

A

thickness of the patient and the depth of the tumor

80
Q

thicker areas of the body –> use __higher//lower__ beam energies

thinner areas of the body –> use __higher//lower__ beam energies

A

thicker areas use HIGHER beam energies
thinner areas use LOWER beam energies

81
Q

pelvic tumors would use what type of beam energy?

A

higher beam energies - like 15 or 18 MV

82
Q

HN tumors would use what type of beam energy?

A

lower beam energies - like 6 MV

83
Q

T/F:

different beam energies have THE SAME depths for dmax

A

FALSE

different beam energies have DIFFERENT depths for dmax

84
Q

what is the dmax of energy 6MV

A

1.5 cm

85
Q

what is the dmax of energy 10MV

A

2.5 cm

86
Q

what is the dmax of energy 15MV

A

3.0 cm

87
Q

what is the dmax of energy 18MV

A

3.2 cm

88
Q

what is the dmax of energy 6MeV

A

1.5 cm

89
Q

what is the dmax of energy 9MeV

A

2.2 cm

90
Q

what is the dmax of energy 12MeV

A

2.8 cm

91
Q

what is the dmax of energy for Co-60

A

.5 cm

92
Q

what is the dmax of energy 25MV

A

5.0 cm

93
Q

what is the dmax of energy 20MV

A

3.5 cm

94
Q

what is the dmax of energy 4MV

A

1 cm

Procedures: 2. DOSI/Treatment Volume Localization (7 decks)

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