Benchmarking a New Circular Cone-based Radiosurgery System against Clinically Tested Radiosurgery System on the same Novel Digital Linear Accelerator Platform

Objective: To examine the dosimetric characteristics of circular cones, the accuracy of dose modeling and overall treatment delivery of two radiosurgery systems integrated on a linear accelerator (Linac). Materials and Methods: The dosimetric characteristics of circular cones (4-17.5 mm) from Varian (VC) and BrainLAB (BLC) were measured for 6 MV flattening filter free beam from Edge linac using stereotactic field diode and 0.65 cc ionization chamber following established protocols. The Eclipse and iPlan modeled dose distribution for VCs and BLCs were validated with EBT3-film measurement. End-to-end tests were performed using stereotactic phantom having PTW 60008 diode connected to a Dose-1 electrometer. Results: The depth at dose maximum, TRP1020 and dose at 10cm depth of the same size VC and BLC agree within +/- 0.7 mm, +/- 0.71% and +/- 0.81% respectively. Full width at half maximum (FWHM) of any cone beyond 15 mm depth increases at 1% of nominal cone size per 10 mm depth. The penumbra of 4mm and 17.5mm VC at 15 mm depth was 1.1 mm and 1.50 mm. At 300 mm depth, penumbra increased by around 0.4 mm for 4 mm cone and up to 1 mm for cone size >= 12.5 mm. The VCs penumbra values were within +/- 1mm of the corresponding BLCs. Scatter factors for VCs varies from 0.609 to 0.841 and were within +/- 1.0% of corresponding values of BLCs. Agreement between the Eclipse and iPlan computed dose fluence and the EBT3-film measured dose fluence was >98% (gamma: 1%@1 mm), and the absolute dose difference was <= 2.2%, except for the 4 mm cone in which it was >96% and <= 4.83%. Target localization using cone-beam computed tomography was accurate within +/- 0.8 mm and +/- 0.3 degrees in translation and rotation. The end-to-end dose delivery accuracy for both radiosurgery systems was within +/- 3.62%. Conclusion: The dosimetric characteristics of Varian and BLC cones of same diameter was comparable. Both Eclipse and iPlan cone planning system modeled dose fluences agree well with the EBT3 film measurement. The end-to-end tests revealed an excellent target localization accuracy of Edge linac with satisfactory and comparable absolute dose agreement between Varian and BLC radiosurgery systems and hence these can be interchanged on edge linac.