Comprehensive investigation into the stability of Varian and Elekta kV imaging systems during arc delivery

Abstract

In radiotherapy treatments utilizing accelerator gantry rotation, gantry-mounted kilovoltage (kV) imaging systems have become integral to treatment verification. The accuracy of such verification depends on the stability of the imaging components during gantry rotation. In this study, a simple measurement method and accurate algorithm are introduced for investigation of the kV panel and source movement during gantry rotation. The method is based on images of a ball-bearing phantom combined with a Winston-Lutz phantom, and determines the movements of all the mechanical parameters of the kV imaging system relative to the reference at zero gantry angle. Analysis was performed on different linear accelerators and both gantry rotation directions. The precision of the method was tested and was less than 0.04 mm. This method is suitable to be included in the quality assurance testing of linacs to monitor the kV imaging system performance and provides additional mechanical information that previous tests cannot.

Variation in isocentre location of an Elekta Unity MR-linac through full gantry rotation

“…Longitudinal misplacement of the BB resulted in a constant shift in MVI pixel value; however, this was accounted for within the method, and trigonometrically not expected to further influence the results. Likewise, cross-plane misalignment of the BB resulted in a sinusoidal pattern, but this was accounted for by subtraction of the first harmonic, in a method that has shown to be reliable in other studies (Rowshanfarzad et al 2012, 2014, Wright et al 2020.…”