Commission of volumetric modulated arc therapy with electronic portal image device

Objective To apply electronic portal imaging device (EPID) in the quality assurance of volumetric modulated arc therapy (VMAT) delivered by TrueBeam linear accelerator. Methods The Shaper software and Eclipse treatment planning system (TPS) were used to edit the VMAT plan delivered by TrueBeam linear accelerator. The EPID was used to evaluate the setup accuracy of multi-leaf collimator (MLC) and clinical dosimetry. TA: a field with a size of 0.5 cm×20.0 cm was exposed with gantry angles of 0°, 90°, and 270°, respectively; TB: the flatness and stability of the field were tested with different combinations of dose rate and gantry angle speed; TC: the setup accuracy of MLC was evaluated with or without rotation; TD: the accuracy of speed change control of MLC was evaluated with or without rotation; TE: the accuracy of simultaneous changes in dose rate and gantry angle speed was evaluated; TF: Clinical patients were evaluated. The Matlab software was used to analyze the results. Results TA: the full width at half maximum of superimposed fields exposed with gantry angles of 0°, 90°, and 270°was 0.39 mm larger than that of the field exposed with a gantry angle of 0°. TB: the difference in flatness was less than 0.5% between fields with different combinations of dose rate and gantry angle speed. TC: the maximum difference in field center was 0.45 mm between EPID measurement and TPS setting. TD: the maximum difference in MLC position was 0.69 mm between EPID measurement and TPS setting. TE: the maximum difference was 0.42 mm between fields. TF: for all the patients, the lowest γ passing rate was 96.4% according to the criterion of 3%/3 mm. Conclusions EPID is an accurate and convenient approach for VMAT quality assurance, which provides an option for physicists to reduce workload. Key words: Electronic portal image device; Volumetric modulated arc therapy; Quality control