Clinical experience with machine log file software for volumetric-modulated arc therapy techniques

Mobius FX, an add-on software module from Mobius Medical Systems™ for intensity-modulated radiation therapy (IMRT) quality assurance (QA), uses linac treatment logs to efficiently calculate and verify the 3D dose delivered to patients. An advantage of the Mobius FX module is that it does not require device positioning. In this study, we compared the Mobius FX with another QA option, ArcCheck, as well as with the treatment planning system (TPS) using 30 volumetric-modulated arc therapy (VMAT) plans planned and delivered on a Varian TrueBeam linac. The plans, which involved 6 and 10 MV and consisted of 2 to 3 arcs per plan, were selected to provide a clinically relevant sample. The average gamma value for all plans between Mobius FX and the TPS was 99.96% for the criterion of 3%-3 mm and 98.80% for the criterion of 2%-2 mm. Very similar results were found when comparing Mobius FX and the TPS dose calculations with those acquired by traditional methods (i.e., ArcCheck). As the gamma criterion of the analysis was narrowed, discrepancies between Mobius FX and traditional methods appeared. Profile analysis showed the production of comparable results when using the Mobius FX method or traditional QA methods. In conclusion, the Mobius FX method for pretreatment of patient-specific QA is capable of producing results similar to those obtained by traditional methods.