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Evaluation of the Correlation Between Two Respiratory Monitoring Systems Using External Surrogates for 4DCT

J Liu

J Liu*, T Lin , J Fan , C Ma , L Chen , R Price , Y Dong , Fox Chase Cancer Center, Philadelphia, PA


SU-H2-GePD-J(B)-5 (Sunday, July 30, 2017) 3:30 PM - 4:00 PM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: The purpose of this study is to evaluate the differences in the respiratory signals acquired by two different external surrogates for 4DCT treatment simulation and gated beam delivery: the Varian RPM system and the Siemens ANZAI belt system.

Methods: Fifteen patients with regular breathing patterns were included for data acquisition and analysis. Both the ANZAI pressure sensor and the RPM infrared reflecting marker were placed on the abdominal surface during 4DCT scanning on a Siemens SOMATOM Definition AS (Open 20 RT). The two monitoring systems were started simultaneously to acquire respiratory signals. Only the RPM system was connected to the scanner to receive the beam on/off signals for online image reconstruction. The ANZAI data was retrospectively aligned with the RPM data and the peaks/valleys on the breathing traces corresponding to the end of inhalation/exhalation were searched to calculate the breathing periods and depths. The phase shift between the two breathing traces was calculated by the time latency at the end of inhalation. Individual breathing cycles were extracted and renormalized to compare breathing patterns from both systems.

Results: The breathing periods and depths measured by the RPM and ANZAI systems were found to be in good agreement for all patients. The average phase shift between the two breathing traces was 0.2±0.1second for all patients and the maximum phase shift was >0.4second for 1/3 of patients. The average breathing pattern measured by the ANZAI system had a steeper falloff curve during exhalation than that by the RPM system.

Conclusion: The phase shift and difference in breathing pattern between the RPM and ANZAI systems may result in differences in 4D images, indicating that these two systems are not equivalent external surrogates. The same system must be used in designing the gating window from 4DCT and in monitoring the gated treatment for consistency.

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