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Characterization and Validation of SRS MapCheck for Patient Specific QA On CyberKnife M6

D Parsons1*, C Ding1 , B Zhao1 , T Chiu1 , L Tirpak2 , R Reynolds1 , Y Park1 , Y Yan1 , S Jiang1 , X Gu1 , (1) UT Southwestern Medical Center, Dallas, TX, (2) Sun Nuclear Corporation, Melbourne, FL


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 4

Purpose: We develop and validate a method for using Sun Nuclear Corporation’s SRS MapCHECK™ (SRS-MC) for CyberKnife-M6 patient specific QA over the range of collimators and treatment paths used clinically.

Methods: The array calibration for SRS-MC was carried out using a 6MV beam on TrueBeam. The array calibration was updated for CyberKnife beam quality using the StereoPHAN™ Factor calibration procedure and a 60mm fixed-cone at a source-to-detector (SDD) distance of 80cm for AP and PA beams. The diode array of SRS-MC was characterized for the effects of varying SDD (60-120cm), angular position, and output factor. A nominal SDD and MLC field size of 80cm and 50x53mm², respectively, were used. Dose calibration was preformed by creating a single-shot plan and scoring dose to the central area of the diode array for both a 60mm fixed-cone and 50x53mm² MLC field. 30 previously treated patient plans were tested for QA. For all plans, the fiducial markers with SRS-MC were used for image-guidance. The plans contained prostate, body, and head paths for MLC, iris and cone collimation. All QA plans were analyzed using the gamma criterion of 2%/1mm. Additionally, central axis dose was recorded.

Results: Compared to the nominal, the diodes under- and over-respond by -1.2% and 2.2% at 60-120cm SDD. Output factor varies by -0.7% and 0.9% at fields of 7x7mm² and 70x70mm² compared to the nominal. Approaching 90° to the array, the diodes under-respond by -1.7%. The mean gamma pass rates were 95.0%, 98.1% and 94.4% for the MLC, iris and fixed-cone collimators, respectively, over all plans. Corresponding measured central axis doses were -1.9±0.8%, -1.8±1.5%, and -0.4±4.7% from planned.

Conclusion: The use of SRS-MC has been characterized and validated for patient specific QA on CyberKnife for a variety of clinical plans. The results show that SRS-MC is well suited for this task.

Funding Support, Disclosures, and Conflict of Interest: Lena Tirpak is employed by Sun Nuclear Corporation and the SRS MapCheck was loaned to UTSW for testing and development.


Quality Assurance, Stereotactic Radiosurgery, Diodes


TH- Radiation dose measurement devices: diodes/solid state

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