ABSTRACT
Standard linear accelerators now routinely include flattening filter-free (FFF) beams; these beams are sufficiently different from conventional flattened beams to require special considerations and occasionally unique corrections. This chapter reviews these considerations, highlighting the following: Due to the shape of the beam profile, a geometric correction factor is needed for reference dosimetry with Farmer type chambers. Because of the higher dose rates recombination effects are more pronounced and may become an issue in selected ionization chambers. While the spectrum for FFF beams is more uniform across the treatment field, it is generally softer, so that detectors with a pronounced energy dependent response should be cross calibrated before use in an FFF beam.
