CT Simulation Flashcards
what is the most common imaging modality used for radiation therapy treatment planning?
computed tomography (CT)
how are CT images produced?
hint - don’t overthink. Literally think what you sit at and see when doing a CT
by using an x-ray, detectors, and computer
T/F:
computed tomography CT is axial or spiral/helical
TRUE
what does it mean that computed tomography CT is axial spiral/helical?
just means the couch moves as the x-ray tube rotates within the gantry
what unit measures beam quantity?
Milliamperage (mA)
what does “beam quantity” mean?
hint - literally QUANTITY
how many x-rays are produced
an increase in mA leads to what?
an increase in patient dose
what is the CT tube current measured in?
coulomb/sec
slice ______ and the ____ between slices are key factors for generating high-quality digitally reconstructed radiographs (DRRs)
slice thickness, and
space between the slices
what does DRR stand for?
Digitally Reconstructed Radiographs
what should spacing be BETWEEN slices for CT?
hint - lower than __
lower than 5mm
what should slice thickness typically be set to for CT?
hint –> __ - __
2-3 mm
Imaging Terminology -
the following describes what?
“the diameter of the area being scanned”
FOV (Field of View)
Imaging Terminology -
the following describes what?
“area of interest to be scanned”
Scan field of view *our scouts
Imaging Terminology -
the following describes what?
“the number of shades of gray displayed on an image or the contrast of the image”
Window width (WW)
Imaging Terminology -
the following describes what?
“the MEDIAN shade of gray or HU (Hounsfield unit) WITHIN THE window width”
Window level (WL)
a narrow Window Width on a CT would have MORE or LESS contrast?
MORE
what Imaging Terminology changes the image brightness?
window level
an INCREASE in window level creates a BRIGHTER or DARKER image?
Darker image
a DECREASE in window level creates a BRIGHTER or DARKER image?
Brighter image
Imaging Terminology -
the following describes what?
“a value that represents a shade of gray, also known as the HU (Hounsfield unit)”
CT number
CT number can also be called a ___________
Hounsfield unit (HU)
what do CT numbers represent?
the density of different tissues (electron density)
what do CT numbers range from?
hint - negative number to positive number
-1000 to +1000
what does CT number -1000 represent?
air
what does CT number +1000 represent?
bone
what does CT number 0 represent?
water
Imaging Terminology -
the following describes what?
“the computer uses algorithms to create the CT image in different planes”
Reconstruction
what views (2) are reconstructed from axial slices?
Coronal and Sagittal
Coronal and Sagittal views are constructed from ___ slices
axial
the following is of what body plane?
axial/transverse
the following is of what body plane?
coronal
the following is of what body plane?
sagittal
_______ look like plain 2D radiographs and are reconstructed from the CT slices to show a beam’s-eye-view
DRRs (digitally reconstructed radiographs)
what does BEV stand for?
Beam’s Eye View
DRRs are made to compare to what?
compare to portal images (ports)
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
contour
a ________ is a representation of the patient and is necessary for creating accurate treatment plans and calculating doses
contour
T/F:
Target volumes, critical structures, and other anatomy are defined on the CT, MRI, and/or PET images
TRUE
T/F:
Multiple studies from different imaging modalities can be fused together to give even more information to those planning the treatments (ie. dosimetry)
TRUE
it is common to fuse ___ images and ____ images together
MRI and CT
MRI scans are useful to show Hard OR Soft tissues
soft
MRI and CT scans are commonly fused together to better highlight what anatomy?
prostate
_____ scans are useful because they show the activity of the tumor
PET
____ scans and ____ scans are commonly fused together to show areas of activity in sites such as the lung, and head and neck.
PET and CT
what are the two different ways to plan a treatment once all the data is gathered? ________ planning and _______ planning
inverse planning
forward planning
Which planning is being described below? - Forward or Inverse
- the planner chooses the energy, appropriate dose to the tumor, and the tolerances of the normal healthy tissues
- the computer then creates a plan using MLC pattern, shapes, directions, etc.
- used in IMRT (Intensity-Modulated Radiation Therapy)
Inverse planning
Which planning is being described below? - Forward or Inverse
- the planner chooses the energy, number, shape, and direction of the radiation beams
- the computer calculates the isodose lines, and the planner must assess the dose distribution and make changes if necessary
Forward planning
what ways can images be transmitted and stored? (3)
____ tapes
____ disks
____ network
magnetic tapes
optical disks
electronic network
what does DICOM stand for?
Digital Imaging and Communication in Medicine
what system creates the standard format to transfer images from imaging computers to the treatment planning computer?
DICOM (Digital Imaging and Communication in Medicine)
what does PACS stand for?
Picture Archiving and Communication System
what system is used to store and share images electronically?
PACS (Picture Archiving and Communication System)
_____ 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
lasers
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
three
within treatment and simulation rooms, lasers are located ______, ______, and _______ on the ceiling in the ____, ____, and ____ coordinates
laterally, sagittally, and overhead
X, Y, and Z
label the coordinates
1.
2.
3.
1 - Z
2 - Y
3 - X
one CT slice dose @ skin is equal to ___ to ___ cGy (or __-___ mSv)
1-6 cGy
2-10 mSv
CT sim terminology
define “Pixel”
picture element; each cell on the image matrix; 2D representation of tissues
CT sim terminology
define “Voxel”
volume of element; contraction for volume element, which is the basic unit of CT or MR reconstruction
“each cell on the image matrix; 2D representation of tissues” is describing what CT terminology?
PIXEL
“volume of element; contraction for volume element, which is the basic unit of CT or MR reconstruction” is describing what CT terminology?
VOXEL
CT sim
bone attenuation happens through ______ & _______ scattering
Photoelectric effect and
Compton scattering
with a CT number of +1000, ____ appears ____ on a CT due to it’s higher density
bone appears white
with a CT number of -1000, ____ appears ____ on a CT due to it’s low density
air appears black/dark
what is white?
-orange?
-blue?
Z = white
X = orange
Y = blue
which lasers move -
CT room or TRT room lasers?
which lasers are stationary (ie. do not move)
CT lasers can move
TRT room lasers do not move
Total Target Dose is the ____ dose
absorbed dose
Total dose is dependent on _____ and _____
location of the tumor and organs at risk
what is a typical Curative dose?
180-200 cGy daily fraction
for a total of 5400-6000 cGy
what is a typical Palliative dose?
300 cGy daily fraction
for a total dose of 3000 cGy
describe Boost/Cone-down
a smaller field that can give a higher dose
absorbed dose is measured in what?
normally measured in Gy (Gray)
100 rads = ___ Gy
1 Gy
what is the most common fractionation schedule?
once a day –> for 5 days –> for several weeks
number of fractions vary with the _____ _____ dose
total tumor dose
BID means what?
twice per day
what is the MINIMUM amount of hours you HAVE to wait between BID trts?
MINIMUM 6 hours
beam energy is dependent on the ______ of the patient and the ______ of the tumor
thickness of the patient and the depth of the tumor
thicker areas of the body –> use __higher//lower__ beam energies
thinner areas of the body –> use __higher//lower__ beam energies
thicker areas use HIGHER beam energies
thinner areas use LOWER beam energies
pelvic tumors would use what type of beam energy?
higher beam energies - like 15 or 18 MV
HN tumors would use what type of beam energy?
lower beam energies - like 6 MV
T/F:
different beam energies have THE SAME depths for dmax
FALSE
different beam energies have DIFFERENT depths for dmax
what is the dmax of energy 6MV
1.5 cm
what is the dmax of energy 10MV
2.5 cm
what is the dmax of energy 15MV
3.0 cm
what is the dmax of energy 18MV
3.2 cm
what is the dmax of energy 6MeV
1.5 cm
what is the dmax of energy 9MeV
2.2 cm
what is the dmax of energy 12MeV
2.8 cm
what is the dmax of energy for Co-60
.5 cm
what is the dmax of energy 25MV
5.0 cm
what is the dmax of energy 20MV
3.5 cm
what is the dmax of energy 4MV
1 cm
