Dose 2016

Energy dependence due to changing Stopping-power ratios

6 MV photon beam n=narrow beam ( ∅ =0.5 cm) b=broad beam ( ∅ =10 cm)

Cylindrical air ion chambers can be used without correction for energy variations in high energy photon beams, incl. Co- 60 (IAEA TRS-398).

The secondary electron energy spectrum is not changing with depth.

Heydarian et al

Ratio narrow/large field depth dependence Difference <0.5%