Course book Advanced Treatment Planning 2018

Pencil beam kernel

Calculation object approximations with heterogeneities

Effects of heterogeneities are generally modelled in pencil kernel algorithms through depth scaling along rayline (and no lateral scaling). Correct handling of heterogeneities requires proper 3D modelling of the secondary particle transport.

 0  1

z

eq

Primary deposition volume

 1 illustrates a low density region, e.g. lung tissue.

Calculation point

Heterogeneous slab phantom

 1

z

z

z

 1

eq

 0

 0

 0

 1

Primary deposition volume

Primary deposition volume

Primary deposition volume

Calculation point

Calculation point

Calculation point

Scatter underestimated

Scatter and primary overestimated

Scatter overestimated