TG-179 Values and Information

Question 1

What are the recommended daily tests for CT based IGRT systems? And their respective tolerances

Answer 1

Safety (collision interlocks, warning lights)

Laser/image/treatment isocenter coincidence (+- 2mm)

Phantom localization and repositioning with couch shift (+- 2 mm)

Question 2

How often do you need to perform geometric calibration maps?

Answer 2

Monthly or upon upgrade

Question 3

How often do you need to measure couch shift accuracy?

Answer 3

Monthly

Question 4

Tolerance for kV/MV/laser alignment

Answer 4

+- 1 mm

Question 5

Tolerance for couch shifts

Answer 5

+- 1 mm

Question 6

What image quality tests are required monthly?

Answer 6

Scaling
Uniformity
Noise
High contrast spatial resolution
Low contrast detectability

• CT number accuracy (but only if IGRT is used for dose calculation)

Question 7

How often should you measure imaging dose?

Answer 7

Annually

Question 8

Typical dose for Varian OBI (CBCT)

Answer 8

0.2 - 2.0 cGy