ESTRO course Dose Modelling and Verification 2017

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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.

T Knöös

Warsaw 2017