FFF

Question 1

Remove the filter
* What are the intended
consequences?

Answer 1

• Dose rate increase
• Decrease dose delivery time
  ‒ Efficiency
  ‒ SBRT/SRS

Question 2

Consequences

Answer 2

-Dose rate increases
-Less beam hardening
-Less variation in off-axis beam hardening
-Less photon head scatter
-Less leakage outside of the beam collimation

Question 3

-Less variation in off-axis beam hardening

Answer 3

-FFF = beam is more uniformly “unhardened”
since the FF not uniformly thick, hardening was best in central axis

Question 4

Less photon head scatter

Answer 4

ff is the first thing the beam hits tf scatter
FFF= ↓ field size dependence

Question 5

Less leakage outside of the beam collimation

Answer 5

50% reduction

Question 6

Problems with removing the filter

Answer 6

-Ionisation chamber and EPID saturation
-↑Interleaf leakage
-Surface dose is higher/different

Question 7

-Ionisation chamber and EPID saturation

Answer 7

Dead time in the detectors means that there are periods where they don’t count ionisation= silent undercounting

Question 8

Surface dose is higher/different

Answer 8

↑electron contamination
↑proportion of low energy photons