Dose Course 2018_Flipping book

Mean energies in a 6 MV beam depending on field size and depth

Two counteracting effects as depth increases: Beam hardening of primary fluence and increasing amount of scattered photons.

photons

electrons

~0.16 MeV (1/10)

~0.7 MeV (1/3)

Incident mean photon energy = 2.11 MeV

Heydarian et al