TG-66 Memorizing information Flashcards
How often do you measure CT number accuracy?
Daily for CT number of water only
Monthly for 4 to 5 difference materials
Annually for a electron density phantom
Tolerance for daily CT number accuracy
0 +- 5 HU
How often do you measure image noise?
Daily
In-plane spatial integrity tolerance
1 mm
How often do you measure in-plane spatial integrity?
Daily for x or y direction
Monthly for both directions
When do you measure field uniformity and for what kVp settings?
Monthly - most commonly used kVp
Annually - other used kVp settings
What kVp’s do we use in our clinic?
140 kVp for everything
Why do we only use 1 kVp setting for all scans?
So we don’t need multiple HU maps for eclipse
Field uniformity tolerance
Within +- 5 HU
When are you supposed to measure spatial and contrast resolution?
Annually, but we do it monthly as well
Tolerance for spatial and contrast resolution
Vendor specification +- 1 visible node on catphan
How often should you measure CT slice width?
Monthly
Frequency of patient dose from CT-scan, CTDI measurement
Annually
Frequency of table movement and positioning tests
Monthly
Frequency of artifact evaluation
Monthly
What are some common CT artifacts?
Beam hardening (cupping artifact, streak and dark bands, metal artifacts) Metal artifacts Ring artifacts Motion artifacts Photon starvation Partial volume averaging Truncation artifact
Bore size of a CT sim
Bore size of a standard CT
CT sim: 85 cm
Standard CT: 70 cm
Three differences between CT sim and a regular CT
Flat couch top
Lasers
Larger bore
Why does TG 66 recommend not having a beam interlock for door opening?
Interrupting a scan means you need to redo it, resulting in more dose to patient.
Dose to anyone entering room during scan is much lower than dose to patient, so it’s not worth stopping.
Also, additional concerns for contrast scanning
