Abstract：Objective To measure the radiation field shape, size, penumbra and other dosimetric parameters of a rectangular collimator
Gamma knife, and to analyze the dose distribution formed by the radiation field focus, static and dynamic arc to obtain the dosimetric
characteristics of rectangular collimator Gamma knife. Methods EBT3 films were used to measure the dose distribution of different
radiation fields on the Luna-260 Gamma knife. The dosimetric parameters of the rectangular collimator were obtained by the film
analysis software. The collimators No.3 and No.6 were selected for focusing at different angles in the radiotherapy planning system,
and the dose lines formed on different cross sections were analyzed. Results The radiation field size and penumbra measurement
results of the rectangular collimator met the requirements of the national standard WS 582-2017 Specifications for Testing of Quality
Control in X and γ Ray Stereotactic Radiotherapy System. The size deviations of No.1 to 6 collimator were all within 1 mm, and
the maximum value of the static focusing field penumbra was 4.3 mm. The dose distribution shape of the three cross sections (cross
section, coronal plane and sagittal plane) was related to the size of the arc angle. For the 50% dose line size, in the Z direction, the
50% dose line size of the two kinds of collimator was about 14 mm. In the X and Y direction, the 50% dose line size of the two
kinds of collimator was different, in which the change amplitude of the No.3 collimator was larger, and the change amplitude of the
No.6 collimator was smaller. Conclusion The field size and penumbra size of the rectangular collimator meet the requirements of
the national standard. The arc angle of the rectangular collimator affects the dose distribution, and its dosimetric characteristics can
provide reference for clinical application.
