TG-66 Memorizing information

Question 1

How often do you measure CT number accuracy?

Answer 1

Daily for CT number of water only
Monthly for 4 to 5 difference materials
Annually for a electron density phantom

Question 2

Tolerance for daily CT number accuracy

Answer 2

0 +- 5 HU

Question 3

How often do you measure image noise?

Answer 3

Daily

Question 4

In-plane spatial integrity tolerance

Answer 4

1 mm

Question 5

How often do you measure in-plane spatial integrity?

Answer 5

Daily for x or y direction

Monthly for both directions

Question 6

When do you measure field uniformity and for what kVp settings?

Answer 6

Monthly - most commonly used kVp

Annually - other used kVp settings

Question 7

What kVp’s do we use in our clinic?

Answer 7

140 kVp for everything

Question 8

Why do we only use 1 kVp setting for all scans?

Answer 8

So we don’t need multiple HU maps for eclipse

Question 9

Field uniformity tolerance

Answer 9

Within +- 5 HU

Question 10

When are you supposed to measure spatial and contrast resolution?

Answer 10

Annually, but we do it monthly as well

Question 11

Tolerance for spatial and contrast resolution

Answer 11

Vendor specification +- 1 visible node on catphan

Question 12

How often should you measure CT slice width?

Answer 12

Monthly

Question 13

Frequency of patient dose from CT-scan, CTDI measurement

Answer 13

Annually

Question 14

Frequency of table movement and positioning tests

Answer 14

Monthly

Question 15

Frequency of artifact evaluation

Answer 15

Monthly

Question 16

What are some common CT artifacts?

Answer 16

Beam hardening (cupping artifact, streak and dark bands, metal artifacts)
Metal artifacts
Ring artifacts
Motion artifacts
Photon starvation
Partial volume averaging
Truncation artifact

Question 17

Bore size of a CT sim

Bore size of a standard CT

Answer 17

CT sim: 85 cm

Standard CT: 70 cm

Question 18

Three differences between CT sim and a regular CT

Answer 18

Flat couch top
Lasers
Larger bore

Question 19

Why does TG 66 recommend not having a beam interlock for door opening?

Answer 19

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