TG180

Question 1

dose deposited by 6 MV CBCT vs 2.5 MV CBCT

Answer 1

dose deposited by 6 MV CBCT (1-5 cGy depending on site) is about twice that deposited for 2.5 MV CBCT

- remember, now we are in Compton region and Compton increases with energy 
- if bony anatomy is being used for matching, can reduce MV dose because bone will have better contrast with soft tissue compared to soft tissue vs soft tissue (due to Compton interaction)

Question 2

dose deposited from kV CBCT

Answer 2

0. 1- 6 cGy (latter is for bone in 10% DVH)

- remember that for PE effect, increasing kVp decreases dose

Question 3

acceptable uncertainty for calculating imaging dose

Answer 3

20%

because imaging dose is generally only
a few percent of the prescribed target dose. As a result, the
uncertainty of the summed dose (therapeutic + imaging) will
still be at a level of 2–3%.