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Comparisons of 4DCT Images Reconstructed by Using Two Synchronized Respiratory Monitoring Systems

J Liu

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


TU-RPM-GePD-JT-5 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Joint Imaging-Therapy ePoster Theater

Purpose: Both RPM and ANZAI belt systems are used in our institution as respiratory monitoring systems for 4DCT image sorting and treatment delivery. The purpose of this study is to compare the 4D images reconstructed using both external surrogates and to assess the feasibility of exchanging use of the two systems in treatment planning and gated treatment.

Methods: Seven lung patients were scanned on a Siemens SOMATOM Definition AS (Open 20RT). The RPM system was connected to the scanner to receive the CT on/off signals for online image reconstruction. The ANZAI belt was also placed on the same patient during scanning. Both monitoring systems were started simultaneously and the CT on/off timestamp in the ANZAI signal was synchronized with the RPM data. The ANZAI file was converted into the RPM data format and imported retrospectively into the CT workstation for image reconstruction. Amplitude sorting was used in both reconstruction processes to obtain 4D images. Auto-contouring was applied to segment the whole lung in all 10 phases. The lung volume and the position of the diaphragm apex were measured and compared phase-by-phase.

Results: In the fused images reconstructed separately from the two respiratory monitoring systems, apparent changes in lung contour and spatial shifts in diaphragm apex were observed. The relative difference in the whole lung volume in the ten phases was between -3.7% and +4.1% on average for the seven patients. The corresponding difference in the location of the diaphragm apex was between -5.1mm and +4mm.

Conclusion: The relatively large differences in the 4D images reconstructed using RPM and ANZAI belt indicated different correlation relationships between the internal thoracic motion and external surrogates. The mixed use of one monitoring system in 4DCT for treatment planning and the other in gated treatment may cause errors in the patient dose distribution.

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