ESTRO course Dose Modelling and Verification 2017

Monitor back scatter

0 b M M M A M b A              0 0 0 0 1 ( ) 1 ( )

• Usually a very small effect • Dominated by low energy charged particles, can be stopped by a protection sheet. • Can be modelled by a monitor’s-eye-view of the collimators: - Distance source to monitor and collimator. - Shape of visible collimator surface. - Empirical constant, 0.3 to 0.4.

monitor

2 mon 2 coll

z

  b A k F  back

z



z z coll 

3

mon

cos



F

A



d



2





z

z





Irradiated collimator area

coll

mon

Irradiated collimator surface

42

PMB 44 p R99-R155