CT Simulation Flashcards
In what plane are CT slices acquired in?
Transverse (axial) plane
What are the 3 viewing planes for CT images?
- Axial
- Coronal
- Sagittal
What is the big advantage of slip ring technology in CTs?
Allows continuous rotation in one direction (reduced scanning time)
What is a fan beam projection?
A fan of data that converges on a vertex, and using rotate-rotate geometry
What is axial scan?
A 360 degree scan of a slice, then the couch advances to the next slice
What is helical scan
A continuous couch and x-ray tube motion
What is view aliasing?
When too few projections are acquired to reconstruct with detail
What is aperture?
The physical opening of CT when taking slices
What is Field of View?
What appears on the image after the scan
T or F
CT offers improved contrast resolution over x-ray imaging
True
NB: Because CT uses collimators to reduce scatter
List the benefits of CT simulation
- Gives an accurate representation of patient in treatment position
- Isocenter placement is quick and accurate
- Flexibility to modify at any point
- BEV display
- Electronic field shaping
- Motion management
- Digital storage
- CT exposure is quantified and recorded
What parameters in the scan protocol are commonly adjusted to get the desired image?
- mAs
- Slice thickness
- Slice increment
- Scan length
- Window width and level
What is the No-Shift method?
This aligns the patient in treatment position, marking reference points directly on their skin, so no additional shifts are needed during radiation therapy setup.
What is the Shift method?
This marks initial reference points, then calculates adjustments based on CT images. Patients are repositioned during treatment setup to align with the planned isocenter for accurate radiation delivery.
What parameters are documented in the sim process?
- Patient position
- Immobilization devices used
- Photo of setup
- Part of patient electronic medical record
- After TP, exported and recorded in Record and Verify system for archival and tx delivery on the linac
What is a DRR?
2A D image generated from CT data (3D), simulating a traditional X-ray. It’s used for patient positioning and verification in radiation therapy to ensure accurate treatment alignment.
What is pitch?
It is the relationship between couch movement and the x-ray beam width
NB: Pitch =
Couch movement each 360 degrees / beam width
What is the effect of having a pitch greater than 1.5?
There’s loss of information. Leads to decreased resolution and decreased dose to patient
T or F
Prospective CT sim is the best choice for DIBH treatment
True
