Development and performance evaluation of a high‐speed multileaf collimator

Multileaf collimator (MLC) tracking represents a promising technique for motion management in radiotherapy. However, the conflict between limited leaf speed/acceleration and the demand for tracking fast target motion is now a prominent issue. Conventional MLCs typically have a maximum leaf speed of 3-4 cm/s and a maximum leaf acceleration of 50-70 cm/s2, which are inadequate to track fast target motion. To cope with this problem, we have recently developed a high-speed multileaf collimator (HS-MLC) prototype, which employs linear motors instead of rotary motors to drive leaves. Consequently, it inherits various benefits of linear motors, including direct drive and high dynamics. The primary aim of this paper was to introduce the development and performance evaluation of the HS-MLC. The evaluation includes Monte Carlo simulations of the basic dosimetric properties, camera-based measurements of the mechanical properties and tracking experiments for 25 sets of patient-measured motion data. The Monte Carlo simulation results show that the maximum leakage at 6MV is 1.29% and the average is 0.61%. The end-to-end leakage is 3.96% for 5 cm offset and is 1.75% for 10 cm offset. The penumbra for a standard 10 × 10 cm2 field ranges from 4.8 mm to 5.4 mm across the full range of leaf motion. The mechanical property measurements demonstrate that the maximum leaf speed is 40 cm/s, the maximum leaf acceleration is 1000 cm/s2, and the geometric accuracy can be kept within 0.5 mm. Regarding the tracking experiments for a wide range of motion patterns (fast breathing, irregular breathing, etc.), a root-mean-square error (RMSE) of less than 0.19 mm was achieved. In conclusion, the HS-MLC is able to well track fast target motion that is beyond the capability of conventional MLCs due to its superior mechanical properties. The new MLC design provides a feasible solution to make high-accuracy and high-efficiency motion management possible.