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[Measurement for Maximum Leaf Velocity Using Piecewise Linear Approximation under Constant Acceleration of Multileaf
Masato Fujisawa1, Takahide Hayakawa1, Masaki Ohkubo1
1Department of Radiological Technology, Graduate School of Health Sciences, Niigata University.
Purpose:
The purpose of this study was to propose a method for measuring the maximum leaf velocity (Vmax) 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); Vmax was determined as the velocity in the constant velocity segments. The Vmax 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 Vmax was determined. The mean Vmax 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 Vmax easily.
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