(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: The world’s first EPID-based patient treatment verification system (WatchDog) has been developed to address the important issue of radiation therapy safety to prevent systematic errors and individual isolated errors, resulting in mistreatments. However, respiratory motion has not been verified, which is essential for respiratory-gated liver and lung stereotactic body radiation therapy (SBRT). This study demonstrates that the WatchDog system verifies respiratory motion of lung cancer patients using transit images from EPID.
Methods: Ten respiratory traces (reference) of lung cancer patients, previously acquired using the real-time position management (RPM) system, were utilised as input to a dynamic thorax motion phantom (CIRS, USA) to produce anterior-posterior abdominal motion. Real-time transit EPID images (11Hz) containing encoded respiratory signal measured with the TrueBeam optical system, were continuously acquired with the WatchDog system during radiation delivery. The encoded information of respiratory motion was then decoded retrospectively and compared with the input referenced motion.The Pearson correlation coefficients of two respiratory traces between the reference and the measured motion were computed as a function of their statistical linear relationship. The correlation coefficients in the range from −1 to +1, where +1 (or −1) indicate the strongest possible agreement (or disagreement).
Results: The mean and standard deviation of the correlation coefficients between ten reference and corresponding ten measured respiratory traces was measured at 0.988±0.013 [0.960~0.998], which indicates a very strong correlation.
Conclusion: This study demonstrated that the respiratory traces of lung cancer patients were successfully measured with a high correlation of 98.8% in the WatchDog system. The WatchDog system is applicable to verify respiratory motion for respiratory-gated liver and lung SBRT which has previously not been possible on the Truebeam system.
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