Sensitivity evaluation of two commercial quality assurance systems to organ-dose variations of patient-specific VMAT plans

The purpose of this study was to assess the dose variation sensitivity of two quality assurance (QA) devices (Integral quality monitoring (IQM (R)) and MatriXXEvolution systems) used for radiotherapy verification. Six volumetric-modulated arc therapy (VMAT) radiation plans were calculated, namely, three head-and-neck and three prostate cases. For sensitivity evaluation, the planning target volume (PTV) dose for each patient's plan was modified by 0.5%, 1.0%, 2.0%, and 3.0% of its original dose. The IQM and MatriXX detectors are sensitive to the dose errors considered. At 0.5% PTV dose modification, the average local percentage differences for the IQM are 0.27 +/- 0.29, 0.24 +/- 0.35, 0.42 +/- 0.39, 0.74 +/- 0.28, 0.41 +/- 0.24, and 0.26 +/- 0.32, while the average local percentage differences for the MatriXX device are 1.37 +/- 0.25, 1.30 +/- 0.75, 2.82 +/- 1.46, 1.34 +/- 1.29, 1.58 +/- 0.97, and 1.13 +/- 0.97. The sensitivity of the detectors is more pronounced in VMAT plan errors containing larger segments. This shows that the sensitivities of the detectors are plan and fraction specific. Both detectors are sensitive to dose variation in the clinical plans to a minimal dose deviation of 0.5%. The IQM detector shows the capability to be used for QA procedures and for real-time beam output monitoring.