Evaluation and validation of the machine performance check application for TrueBeam 2.5 Linac

Aim: To evaluate the Machine Performance Check (MPC) 1.1 application for TrueBeam 2.5 and to establish MPC application as a comprehensive daily QA tool after verification. Methodology: An automated daily Quality check application MPC using IsoCal Phantom provided by Varian Medical System (VMS) to perform the essential tests such as beam consistency that is dosimetric performance and mechanical check were performed on TrueBeam. The data was collected over a period of four months (84 days). MPC acquired data consists of a series of generation of images using MV and kV at various gantry, collimator, and couch positions. The collected data is analyzed for daily reproducibility as well as comparison with ion chamber measurements. Findings: The results showed that the reproducibility of MPC was less than the tolerance values for the respective mechanical parameters. The MPC measured isocenter with mean value of 0.35 mm is within tolerance. The Beam Consistency showed that over a period of four months, the mean value of output measurement of 6 MV photon beam as measured by the MPC and Farmer Type Chamber FC65-G differ by less than 1%. It is evident that the MPC proved to be fast and easy to use QA tool for daily checking of machine performance. But it is evident from present study that, inter comparison with a Farmer Type chamber is needed, if the MPC has to replace the other QA tools. Keywords: MPC, QA, Linear Accelerator, EPID AS1000