Dose 2016

57

Summary

The focal spot size (FWHM typically 1-2 mm) influences the photon beam penumbra width. Lateral photon beam flattening through a conical flattening filter also creates additional scatter and increases the off-axis softening effect. Mean photon energy [MeV] at isocenter roughly equals MV/3, somewhat lower for high-energy beams. The geometrical beam alignment is not trivial for rounded leaf edges. It may vary between accelerator vendors and should be better known among users and TPS vendors. Electron beams are strongly influenced by scattering and energy loss interactions inside the treatment head and depends therefore more on treatment head design than photons.

Utrecht 2016