Dosimetric characterization of a novel dual-energy medical linear accelerator without a flattening filter

Abstract

Objective To study the dosimetric characteristics of flattened and flattening filter free (FFF) beams with 6 MV and 10 MV photon energy using a novel dual-energy medical linear accelerator (Elekta Versa HDTM), to identify the dosimetric characteristics and advantages of FFF beams, and to provide a basis for their clinical application. Methods The percentage depth dose (PDD), profiles/dose rate of off-axis ratio (OAR), field size, penumbral width, dose out of the fields, collimator scatter factor (Sc), and total scatter factor (Sc, p) were compared between flattened and FFF beams. Results (1) After beam energy matching, the FFF beams had the same beam energy with the flattened beams. The matching error of PDD at a depth of 10 cm was less than 1% between fields.(2) The FFF beams had a smaller variation in dose rate of OAR with the depth than the flattened beams.(3) The FFF beams had smaller variations in field size and penumbral width than the flattened beams. Moreover, the penumbral width of the FFF beams increased with the increasing field size or depth. The FFF beams had a lower dose out of the fields than the flattened beams.(4) The FFF beams had smaller variations in Sc and Sc, p with the field size and depth than the flattened beams. Conclusions Removal of the flattening filter can substantially improve the dose rate, shorten radiotherapy time, and reduce leakage and scattering of the head. The dosimetric advantages make the FFF beams appropriate for clinical treatment. Key words: Linear accelerator; Flattening filter; Flattening filter free