To study the effect of leaf movement speed on the setup error of multileaf collimator (MLC) in RapidArc mode, and to improve quality assurance and verify the reliability of RapidArc.

Referring to the PicketFenceStatic_M120.dcm and PicketFenceRA_M120.dcm files, the Tilt tests with different adjacent leaf speed were designed and setup errors of MLC were obtained by analyzing electronic portal imaging device images.

In the Tilt tests, the setup errors gradually increased from gap11 to gap50 in both static gantry mode and RapidArc mode. With a gantry angle of 270°, gap41 had the maximum setup error of -0.55 mm. In the RapidArc mode, gap46 had the maximum setup error of -0.67 mm. The deviation of gap width was no greater than 15% in any mode. There was no significant difference in deviation pattern of gap width between four modes with different gantry angles. The same gaps in different stripes showed a consistent trend in gap width. The RapidArc mode had a larger variation in percentage deviation of gap width than the static gantry mode.

The setup error increases with the increase in the speed of MLC leaf. The variation in the leaf speed has no significant impact on the gap width. There is no correlation between the leaf speed and the deviation of gap width. Four different gantry angles give similar deviation patterns of gap width, suggesting that the deviation of gap width is related to the leaf rather than the gantry angle. The RapidArc mode has a greater impact on the gap width than the fixed gantry mode.

RapidArc; Multileaf collimator; Position error