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

Equivalent (uniform) square field sizes of flattening filter free photon beams.
Phys Med Biol. 2017 Aug 03;:
Authors: Lechner W, Kuess P, Georg D, Palmans H
Abstract

 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 flattering 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 as well as published data of the ratio of doses at depths of 20 cm and 10 cm in water (D<sub>20,10</sub>) 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 x 2 cm² to 40 x 40cm². A scatter function that takes the lateral profiles of the individual beams into account was fitted to the experimental data. The lateral profiles of the WFF beams were assumed to be uniform while those of the FFF beams were approximated using 4th or 6th order polynomials. The scatter functions of the FFF beams were recalculated using a uniform lateral profile ...

Source: Physics in Medicine and Biology - August 3, 2017 Category: Physics Authors: Lechner W, Kuess P, Georg D, Palmans H Tags: Phys Med Biol Source Type: research