Dose Course 2018_Flipping book

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.

Dublin 2018