Advanced TP

Penumbra

Lateral scattering:  MCS: penumbra increases with increasing penetration depth.  Exceeds penumbra of photons at some point. Presence of range shifter (combined with low energies):  Substantial increase of spot size.  Dose calculation accuracy for PB algorithm impaired.  Reduce air gap.

Courtesy Palmans 2006.

Water phantom

Low energy High energy

Courtesy Grevillot 2014.