Principles of Radiation Therapy - Ch. 21:
Computed Tomography Simulation
Prior to the use of CT in the simulation process, contouring was performed by use of solder wire or
plaster. - correct answer ✔✔True
Of the four desired qualities of a CT image, which refers to the ability to see shades of gray in the tissue?
- correct answer ✔✔image contrast
What are the varying electron densities displayed as pixels in shades of gray on the imaging screen? -
correct answer ✔✔Hounsfield Units
The dose to the skin surface from a single CT slice is in the range of: - correct answer ✔✔1 to 6 cGy
A CT scanner specifically designed for use in the radiation therapy department should have which
characteristics?
I. high performance scanner
II. laser and patient marking system
III. virtual simulation capabilities - correct answer ✔✔I. high performance scanner
II. laser and patient marking system
III. virtual simulation capabilities
The reconstructed field of view that is displayed on the computer monitor should be large enough to
display:
, I. the entire contour
II. the immobilization device
III. pertinent anatomy only - correct answer ✔✔I. the entire contour
The level of noise on a CT image is affected by which of the following factors?
I. mAs and kVp
II. filtration
III. pixel size
IV. slice thickness - correct answer ✔✔I. mAs and kVp
II. filtration
III. pixel size
IV. slice thickness
Using a higher osmolality substance such as ionic iodine can greatly reduce adverse reactions with
intravenous contrast agents. - correct answer ✔✔False
The window level on a CT image is: - correct answer ✔✔the central Hounsfield unit of all the CT numbers
displayed on an image
Image registration or fusion has all of the following characteristics except - correct answer ✔✔It ensures
that the patient is in the same position for all scans.
Computed Tomography Simulation
Prior to the use of CT in the simulation process, contouring was performed by use of solder wire or
plaster. - correct answer ✔✔True
Of the four desired qualities of a CT image, which refers to the ability to see shades of gray in the tissue?
- correct answer ✔✔image contrast
What are the varying electron densities displayed as pixels in shades of gray on the imaging screen? -
correct answer ✔✔Hounsfield Units
The dose to the skin surface from a single CT slice is in the range of: - correct answer ✔✔1 to 6 cGy
A CT scanner specifically designed for use in the radiation therapy department should have which
characteristics?
I. high performance scanner
II. laser and patient marking system
III. virtual simulation capabilities - correct answer ✔✔I. high performance scanner
II. laser and patient marking system
III. virtual simulation capabilities
The reconstructed field of view that is displayed on the computer monitor should be large enough to
display:
, I. the entire contour
II. the immobilization device
III. pertinent anatomy only - correct answer ✔✔I. the entire contour
The level of noise on a CT image is affected by which of the following factors?
I. mAs and kVp
II. filtration
III. pixel size
IV. slice thickness - correct answer ✔✔I. mAs and kVp
II. filtration
III. pixel size
IV. slice thickness
Using a higher osmolality substance such as ionic iodine can greatly reduce adverse reactions with
intravenous contrast agents. - correct answer ✔✔False
The window level on a CT image is: - correct answer ✔✔the central Hounsfield unit of all the CT numbers
displayed on an image
Image registration or fusion has all of the following characteristics except - correct answer ✔✔It ensures
that the patient is in the same position for all scans.
