TG-142 Values

Question 1

Daily tolerance for laser localization, SRS/SBRT

Answer 1

1 mm

Question 2

Daily tolerance for laser localization, IMRT

Answer 2

1.5 mm

Question 3

Daily tolerance for ODI @ iso

Answer 3

2 mm

Question 4

Daily tolerance for output

Answer 4

3%

Question 5

Monthly tolerance for output constancy

Answer 5

2%

Question 6

Monthly photon and electron beam profile constancy

Answer 6

1%

Question 7

Monthly front pointer test tolerance

Answer 7

1 mm for 100 SSD

Question 8

Monthly Gantry/collimator angle indicators vs digital level tolerance

Answer 8

1 degree

Question 9

Monthly light/radiation field coincidence tolerance for symmetric and assymetric

Answer 9

Symmetric: 2 mm, or 1% on a side
Asymmetric: 1 mm or 1% on a side

Question 10

Monthly Treatment couch LNG, VRT and LAT position indicators tolerance for SBRT/SRS and IMRT

Answer 10

IMRT: 2 mm

SBRT/SRS: 1 mm

Question 11

Treatment couch position indicators pitch, roll and rotation, for SBRT/SRS and IMRT

Answer 11

IMRT: 1 degree

SBRT/SRS: 0.5 degree

Question 12

Monthly CBCT geometric distortion

Answer 12

<= 1 mm

Question 13

Monthly HU constancy tolerance

Answer 13

Baseline +- 50 HU

Question 14

Monthly kV and MV scaling tolerance

Answer 14

MV: <= 2 mm
kV: <= 1 mm (SRS/SBRT)

Question 15

Monthly pattern test tolerance

Answer 15

2 mm

Question 16

Weekly picket fence tolerance

Answer 16

Visual inspection. Clinic chooses tolerance

Question 17

Monthly picket fence tolerance

Answer 17

1 mm

Question 18

Annual flatness and symmetry tolerance

Answer 18

1%

Question 19

Monthly and annual roll-out test tolerance

Answer 19

1 mm

Question 20

Annual temporal accuracy of phase/amplitude gate on and off

Answer 20

100 ms of expectation

Question 21

Daily collimator size indicator tolerance

Answer 21

1 mm SRS/SBRT

2 mm IMRT

Question 22

Annual x-ray output constancy vs dose rate

Answer 22

+- 2%

Question 23

Annual x-ray output calibration tolerance

Answer 23

+- 1%

Question 24

Annual photon beam quality tolerance

Answer 24

1% PDD10

Question 25

Annual electron beam quality tolerance

Answer 25

+-1 mm R50

Question 26

Annual physics wedge transmission factor constancy

Answer 26

+- 2%

Question 27

Describe action level 1

Answer 27

Inspection action

Sudden and significant deviation from expected values that have become normal in your mind from QAing frequently

Values may still be within tolerance, but they should deem inspection if sudden jump

Actions: treatment may continue, but the cause should be investigated

Ex. WL max deltas of 0.8 - 0.9. It’s still within tolerance, but it’s just suspicious. Probably setup error

Question 28

Describe action level 2

Answer 28

Scheduled action

Results of QA procedure that are at or near tolerance

Should cause investigation or scheduled maintence

If a single result exceeds tolerance value, but not by much, you should investigate or schedule maintence

Action: schedule time to correct within next week, but treatment may continue since clinical impact in short amount of time shouldn’t be major

Question 29

Describe action level 3

Answer 29

Immediate action or stop treatment or correction action

Malfunctions or excessive errors that are too significant

You need to stop treatment until it gets fixed

Ex. nonfunctional safety interlocks

Ex. Excessive error in dosimetric quantity (like output)

Question 30

What is the average leaf speed, and what is tolerance for a TG-142 month QA?

Answer 30

Typical average is 2.5 cm/s

Tolerance is - 0.5 cm/s