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CyberKnife Output Constancy Utilizing Daily QA3 Device

T Reynolds1*, M Ozer1 , A Jensen1 , (1) MN Oncology, St Paul, MN


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Major publications on the practice of LINAC quality assurance (QA) recommend an X-ray output constancy check be performed daily. As a part of the daily QA routine, this test should be accurate, efficient and easy to reproduce. The aim of this work was to evaluate the suitability of the Daily QA3 (DQA3) (Sun Nuclear Corporation, Melbourne, USA) device as a QA device for monitoring of X-ray output on CyberKnife (CK) M6 Unit and to validate its practical use over 4 years of clinical application.

Methods: Internal electronics were utilized as fiducials to localize the DQA3 following the CK fiducial imaging tracking method. An isocentric plan using 6 cm fixed cone and delivering 100 MUs was generated with CK Precision DQA3 constancy was established by physicists by comparing DQA3 results against the Accuray recommended daily output setup with 10 paired measurements over 9 days. Thereafter, radiation therapists utilized the DQA3 device to verify the output constancy. Dose and detector calibrations were performed semiannually to maintain accuracy. In addition, monthly ion chamber measurements in solid water were compared to the doses measured with DQA3.

Results: 955 central axis dose measurements were collected with the DQA3 daily. The average daily output was 100.15 ± 1.22 cGy. The output measured with DQA3 device was in a good agreement with monthly output measurements. Percent difference between absolute doses measured with DQA3 and monthly setup was 0.45 ± 1.62 cGy. The DQA3 device showed a good agreement with ion chamber measurements making a suitable device for detection of output variations during routine measurements.

Conclusion: DQA3 is a suitable detector for daily QA of CK beam output constancy.


Quality Assurance, Linear Accelerator, Dose


TH- External beam- photons: cyberknife

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