ESTRO course Dose Modelling and Verification 2017

13

The widening of the pencil is limited

 The pencil-beam width (

 This is due to the reduction of the number of electrons in the beam at large depths due to range straggling

MCS ) as a function of depth agrees well with experiment at small and moderate depths.

 Then it continues to increase, whereas in reality it goes through a maximum and finally decreases.

 This is managed by the g(x) function or has to managed in other ways in some systems

From Handbook of Radiotherapy Physics Ed Mayles, Nahum and Rosenwald

Warsaw 2017