Commissioning of a GyroKnife digital ⁶⁰Co system

Objective: To introduce and evaluate the characteristics of a GyroKnife Digital Cobalt-60 System for stereotactic radiotherapy and radiosurgery in mechanical aspect. Methods: To test the radiation safety, the dose rate required for radiation protection was measured by using an ionization survey meter (Invasion Model 451 B, Cleveland, OH). Micrometer was used to verify the accuracy of the table in movement and protractor to verify the rotation movement range. The 160 mm diameter polystyrene spherical phantom and film were used in measurement of the radiation Full Width at Half Maximum. And the difference between radiation isocenter and mechanical isocenter was also verified. Results: Clinical requirement in radiation protection was met. The maximum error of table movement accuracy was 0.2 cm at Z axis; the maximum error of gantry movement accuracy was 0.1°. For all the collimators, radiation Full Width at Half Maximum (FWHM) was 2.55, 5.40, 10.50, and 18.55 mm and average penumbra was 5.0, 12.4, 30.1, and 51.5 mm, respectively. The maximum difference between mechanical center and radiation center was 1.41 mm. Conclusions: Stereotactic radiotherapy and radiosurgery has good mechanical characteristics and is suitable clinic applications. (authors)