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Initial Validation of the Surface Beacon Transponder

X Tang

X Tang*, Z Saleh , T Volpe , R Margiasso , D Lovelock , X Li , M Chan , M Hunt , J Deasy , Memorial Sloan-Kettering Cancer Center, New York, NY


SU-E-J-63 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Varian’s L shaped surface beacon transponder for the Calypso system has recently been cleared for real time tracking anywhere on body. We herein conduct initial validation of the surface beacon transponder in preparation for clinical implementations.

Methods: The surface beacon transponder was placed on a respiratory phantom to conduct the following three tests. 1) Stability: the phantom was turned on to produce the same breathing cycle repeatedly, and the associated transponder motion was then recorded. The mean and standard deviations of the amplitude were calculated for phase 0% and 50% over all the cycles. We also looked for any possible baseline drift. 2) Reproducibility: the phantom/transponder was setup to the same position multiple times, and motion from each session was recorded. The mean and standard deviation of the amplitude of phase 0% were calculated over all sessions. 3) Transponder placement sensitivity: it is recommended to align two arms of the transponder to the lateral and sagittal lasers. With patient breathing, transponder position might vary during the treatment. We manually introduced 14° yaw to the transponder placement and calculated the amplitude difference compared to when transponder was perfectly aligned (0°).

Results: 1) Stability: the means and standard deviations for 0% and 50% were 1.39±0.01 cm and -0.03±0.005 cm. The baseline seemed to drift up: i.e. the amplitude was shifted slightly higher each breathing cycle. 2) Reproducibility: 1.36±0.02 cm. 3) Transponder placement sensitivity: the amplitudes were 1.55 cm at 14° vs. 1.35 cm at 0°.

Conclusion: The surface beacon transponder appears to be relatively stable and reproducible. More study is needed to confirm the baseline drift. It is important to align the transponder to the lasers, and users should be cautious about the possible amplitude change due to transponder yaws.

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