Equivalent (uniform) square field sizes of flattening filter free photon beams

Various types of treatment units, such as CyberKnife, TomoTherapy and C-arm linear accelerators (LINACs) are operated using flattening filter free (FFF) photon beams. Their reference dosimetry, however, is currently based on codes of practice that provide data which were primarily developed and tested for high-energy photon beams with flattening filter (WFF). The aim of this work was to introduce equivalent uniform square field sizes of FFF beams to serve as a basis of a unified reference dosimetry procedure applicable to all aforementioned FFF machines. For this purpose, in-house determined experimental data together with published data of the ratio of doses at depths of 20 cm and 10 cm in water ( D 20,10 ) were used to characterize the depth dose distribution of 6 and 10 MV WFF and FFF beams. These data were analyzed for field sizes ranging from 2  ×  2 cm 2 to 40  ×  40 cm 2 . A scatter function that takes the lateral profiles of the individ...

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