[Measurement for Maximum Leaf Velocity Using Piecewise Linear Approximation under Constant Acceleration of Multileaf Collimator].

Abstract

Purpose: The purpose of this study was to propose a method for measuring the maximum leaf velocity (V_max) of the multileaf collimator (MLC) in a dynamic MLC irradiation.

Methods: The irradiation was carried out with a plan in which the MLC leaves were constantly and gradually accelerated. Based on this plan, it was assumed that the velocity of each leaf v(t) (t is the elapsed time) would initially increase but plateau once it reached its maximum velocity. In the proposed method, v(t) was calculated from the log file data during irradiation, and fitted by a piecewise linear function consisting of 2 linear segments (constant acceleration and constant velocity segments); V_max was determined as the velocity in the constant velocity segments. The V_max values in each accelerator were obtained periodically for 7 months (20 measurements in total).

Results: In all measurements, the constant acceleration and constant velocity segments in v(t) were clearly distinguished by the piecewise linear approximation, and the V_max was determined. The mean V_max value of each leaf ranged from 3.63 to 4.32 cm/s with standard deviations (SD) less than 0.04 cm/s.

Conclusion: The proposed method made it possible to confirm the long-term stability of the V_max easily.