Physical Characteristics of Fixed and Dynamics Collimator for Cyberknife M6

This research describes the estimation and quantization of physical benefit for the fixed/variable aperture collimator (Iris) of Cyberknife M6. The fixed collimator and Iris were measured of output factors in different depths (650, 800 and 1000 mm) with an ionization chamber inside a water phantom, and the physical characteristic of profile was compared in different depths (5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50 and 60 mm in diameter). The results of this study showed that the great difference of output factor for two collimators is fixed collimator higher than 25.88% with Iris in 5 mm cone size and in SAD 800 mm, and 3.4% for 7.5 mm cone size. The other output factor differences between fixed and Iris are all less than 1%. The biggest different of penumbra of fixed and Iris are in 50 and 60 mm cone sizes.