Physics Bucharest 2017

Dosimetric characteristics → Clinical implications

• Higher DR → Dosimetric equipment (dose rate dependence?– P ion -k q

-partial volume)

→ Radiobiology of HDR? No correction factor recommended → Main advantage FFF for SRT (high fraction dose-small fields– no modulation) → Motion management – reduced treatment time (but interplay?) • Softer spectrum-low energies not removed → Lower effective energy if the electron beam is the same (shallower D max ) → Higher skin dose → But purer spectrum (+ < e - contamination) and easier to model → Reduced variation of energy spectrum across field size (due to different hardening in the field) • Reduced head scatter → Reduced treatment head leakage → Reduced variation of output ratio in air with field size → Lower out of field dose to surrounding tissues (Kragl et al. Z Med Phys 2011;21) • Less neutron dose (less photon fluence/dose and no neutron generated in the FF) → use of higher energy photons?