An alternative effective method for verifying the multileaf collimator leaves speed by using a digital-video imaging system

We present an alternative effective method for verifying the multileaf collimator (MLC) leaves speed using a digital-video imaging system in daily dynamic conformal radiation therapy (DCRT) and intensity-modulation radiation therapy (IMRT) in achieving increased convenience and shorter treatment times. The horizontal leaves speed measured was within 1.76–2.08 cm/s. The mean full range of traveling time was 20 s. The initial speed-up time was within 1.5–2.0 s, and the slowing-down time was within 2.0–2.5 s. Due to gravity the maximum speed-up effect in the X1 bank was +0.10 cm/s, but the lagging effect in the X2 bank was −0.20 cm/s. This technique offered an alternative method with electronic portal imaging device (EPID), charged coupled device (CCD) or a light field for the measurement of MLC leaves speed. When time taken on the linac was kept to a minimum, the image could be processed off-line.