Comparative investigation of beam quality index Q on flattening filter and flattening filter free 6 and 15 MV photon beams of an medical linear accelerator

Abstract

An Elekta Synergy LINACwas used to investigate the beam quality index Q and the beam quality correction factor kQ,which is used for absolute dosimetry, in off-axis photon fields. It was foundthat the beam quality index Q of the photonenergies with flattening filter decreases with increasing distance to the central axis, at 6 MV by 4.27%and at 15 MVby3.98% inside a range of 15 cm off-axis. The beam quality index for flattening filter free photon fields also decreases with increasing distance to the central axis. In this case Q changed only by 1.01% inside the above range.