Room: AAPM ePoster Library
The CyberKnife® Robotic System (Accuray, Inc., Sunnyvale, CA, USA) is a frameless non-isocentric stereotactic radiosurgery system that offers small sized radiation fields for treating small-volume tumors with submillimeter precision. In the present study the relative output factors (OF) were measured using four different dosimeters. Unshielded diodes were selected to minimize the scatter photon contributions.
In this study the OF was measured with four unshielded diode dosimeters for twelve different IRIS collimators at SAD setup of 800 mm and at the depth of 15 mm. The dosimeters used were PTW electron diode, PTW SRS diode, Scanditronix electron diode and Scanditronix SRS diode. The dosimeters were mounted in PTW MP3 water phantom and directly connected to the Unidos E electrometer. The analysis was performed using MEPHYSTO mc2 software.
The average, standard deviation (SD) and range were calculated from the 4 unshielded diode OF measurements. The average OF values agree with the standard values available in the literature to within 1.9%. The largest SD and range of OF were found at the smallest collimator of 5 mm and decreased with increasing collimator size.
OF values of a CyberKnife has been measured with precision using 4 unshielded diode dosimeters for all field sizes. The inter-dosimeter variation showed a decreasing trend with increasing collimator field size.