Beam Commissioning Data Acquisition for the Iris Variable Aperture Collimator of CyberKnife VSI

Objective: To minimize the risk inherent to the use of medical radiation and robotic radiosurgery, this research introduced the basis and method of beam commissioning data acquisition for the Iris variable aperture collimator of CyberKnife VSI. Methods: In this study, clinical dosimetry measurements of the Iris collimator such as tissue-phantom ratios (TPRs), off-center ratios (OCRs), and secondary collimator output factors (OFs) were conducted, and the data was contrasted with that of the Fixed collimator. Results: The Iris data and the Fixed data were not quite different in TPRs in the same radiation field size. Since the difference of the hardware structure,the OCRs and OFs were quite different, especially in small aperture (5, 7.5 and 10 mm) under the same condition of SAD. For example, the maximum discrepancy of the OFs was 26.67% (5mm aperture, 650mm SAD). Conclusion: When Iris aperture makes some change, tungsten segments move fast and form an aperture smaller than that we need, and then recover to the right size, which may affect the results of the measurement, and also the dodecagonal design of Iris results in a problem of leakage radiation on the edge. Keywords: Beam commissioning, Iris Variable Aperture Collimator, tissue phantom ratio, off center ratio, output factor, CyberKnife VSI™.