| Abstract | Background: The newly available ZAP-X stereotactic radiosurgical systemis designed for the treatment of intracranial lesions, with several uniquefeatures that include a self -shielding, gyroscopic gantry, wheel collimation,non-orthogonal kV imaging, short source-axis distance, and low-energy mega-voltage beam. Systematic characterization of its radiation as well as otherproperties is imperative to ensure its safe and effective clinical application.Purpose: To accurately determine the radiation output of the ZAP-X with aspecial focus on the smaller diameter cones and an aim to provide usefulrecommendations on quantification of small field dosimetry.Methods: Six different types of detectors were used to measure relative outputfactors at field sizes ranging from 4 to 25 mm, including the PTW microSiliconand microdiamond diodes, Exradin W2 plastic scintillator, Exradin A16 and A1SLionization chambers, and the alanine dosimeter. The 25 mm cone served asthe reference field size. Absolute dose was determined with both TG-51-baseddosimetry using a calibrated PTW Semiflex ion chamber and measurementsusing alanine dosimeters.Results: The average radiation output factors (maximum deviation from theaverage) measured with the microDiamond, microSilicon, and W2 detectorswere: for the 4 mm cone, 0.741 (1.0%); for the 5 mm cone: 0.817 (1.0%); forthe 7.5 mm cone: 0.908 (1.0%); for the 10 mm cone: 0.946 (0.4%); for the12.5 mm cone: 0.964 (0.2%); for the 15 mm cone: 0.976 (0.1%); for the 20 mmcone: 0.990 (0.1%). For field sizes larger than 10 mm, the A1SL and A16 micro-chambers also yielded consistent output factors within 1.5% of those obtainedusing the microSilicon, microdiamond, and W2 detectors. The absolute dosemeasurement obtained with alanine was within 1.2%, consistent with combineduncertainties, compared to the PTW Semiflex chamber for the 25 mm referencecone.Conclusion: For field sizes less than 10 mm, the microSilicon diode, micro-Diamond detector, and W2 scintillator are suitable devices for accurate smallfield dosimetry of the ZAP-X system. For larger fields, the A1SL and A16micro-chambers can also be used. Furthermore, alanine dosimetry can be anaccurate verification of reference and absolute dose typically measured withion chambers. Use of multiple suitable detectors and uncertainty analyses wererecommended for reliable determination of small field radiation outputs. |
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