Purpose: To investigate and compare the QA Crosschecker beam constancy checks for monthly QA, on a medical linear accelerator (linac), against the departmental daily QA program
Methods: In this study QA Crosschecker manufactured by Standard Imaging (Middleton, Wisconsin) was used on Varian (Varian Medical Systems, Palo Alto, CA, USA) TrueBeam. The QA Crosschecker has 453 air-vented pixel ionization chambers with optimized 5 mm spacing. For monthly QA photon and electron measurements, a 20x20 cm2 square field measurement provides dose output and energy verification, Inline, crossline, and diagonal profiles, symmetry, flatness and wedge check and other parameters such as light-radiation field check, CAX field width and penumbra. The base lines for measurements were set when the annual and TG51QA on specific machine was performed. The tolerance for dose output was set ±1.5% from base line, and for the flatness and symmetry 1% difference from base lines. The study was performed over a 12-month period, which allows an assessment of the QA Crosschecker stability and sensitivity to drift of the Linac systems being tested. The study provides routine monthly QA results in a form that is directly comparable to the equivalent Daily QA3 and Machine Performance Check (MPC), when available, on that specific day.
Results: The consistency and performance of the QA Crosschecker indicate a close match and agrees with the Daily QA3, with a maximum difference of 1.3% in the beam output. QA Crosschecker beam consistency check were within tolerance set by the user. However, there was some inconsistency regarding the 6 MV dose output. This can be related to some inconsistency in the machine’s output itself.
Conclusion: Evaluating the results compared to independent checks, the QA Crosschecker could be easily and safely used for monthly QA and even daily checks.