CoP for Non Standard linacs

Question 1

What field do you need to create if your linac can’t make a 10x10 field?

Answer 1

A machine specific reference field

Question 2

What factors need to be corrected?

Answer 2

The quality index and field size

Question 3

What are the reference factors for Tomotherapy?

Answer 3

5cm deep, 85cm SSD, phantom width>= field+5cm, backscatter>=5cm.

Question 4

If a machine is unable to make a large enough field for reference dosimetry what is an alternative?

Answer 4

Make a uniform field out of composite non-uniform fields. This is called a plan class specific reference

Question 5

What are the requirements of composite fields?

Answer 5

Must ensure the chamber reacts well to composite fields.

Needs to produce a uniform field large enough for reference dosimetry.

Question 6

For composite fields what term is added to the equation D=RN?

Answer 6

kfc - accounts for difference in chamber response between machine specific reference and plan class specific reference.

Question 7

For the A1SL chamber in a low gradient field what is the value of kfc?

Answer 7

1