Fig. 1. SRS collimator: (a) collimator of Elekta Linac; (b) collimator of Elekta Gammaknife

Fig. 2. Conical through-hole collimator: (a) physical photo of collimator; (b) side view; (c) top view; (d) bottom view

Fig. 3. (a) Schematic diagram of pernumbra; (b) schematic diagram of field size

Fig. 4. Conical pipe-embedded collimator: (a) side view; (b) top view; (c) bottom view;

Fig. 5. Monte Carlo simulation of conical pipe-embedded collimator in GEANT4: (a) structure of the conical pipe-embedded collimator; (b) the model of collimator (white) and spherical water-equivalent phantom; (c) Monte Carlo simulation of the reaction of collimator and gamma ray, green lines are the simulated trace of γ ray (color online)

Fig. 6. Physical photo of conical pipe-embedded collimator

Fig. 7. spherical water-equivalent phantom

Fig. 8. Dose calibration film

Fig. 9. (a) Film of conical through-hole collimator; (b) film of conical pipe-embedded collimator

Fig. 10. Dose-gray calibration curve

Fig. 11. Monte Carlo simulation: (a) dose distribution at isocenter of conical through-hole collimator; (b) dose distribution at isocenter of conical pipe-embedded collimator (color online)

Fig. 12. Off-axis dose line comparison of two kinds of collimator via Monte Carlo simulation at isocenter (color online)

Fig. 13. Off-axis dose line comparison of two kinds of collimator via film measurement (color online)

Fig. 14. Off-axis dose line comparison of film measurement and Monte Carlo simulation of two kinds of collimator (color online)