Author: Teh Lin, Anna Oneil π¨βπ¬
Affiliation: Fox Chase Cancer Center π
Purpose: Four-dimensional computed tomography(4DCT) is often required to assess organ motions for thoracic and abdominal cancer patients. This study proposes a quality assurance (QA) procedure for two external respiratory monitoring systems: the ANZAI Respiratory Gating System and the RPM (Varianβs Real-Time Position Management) used during 4DCT to record breathing on Siemens DefinitionAS 4DCT scanner.
Methods: Our proposed QA involved mechanical and volume end-to-end tests. The mechanical QA evaluates the Anzai sensor and RPM linearity. We placed various weights on top of the ANZAI pressure sensors (Deep/Standard cell) and adjusted the motion lengths to alter the RPM infrared marker ranges on the detection screen. Pressure and displacement were measured using the ANZAI-AZ733V software and the RPM camera readout system. These measurements were conducted at different motion speeds (10 or 15 cycles per minute) with varying scan parameters (6, 9, or 12 respirations per minute). End-to-end tests of three-ball phantom volume were conducted with various speed and scan parameters. Theoretical volume (TV) of the phantom was compared to the volumes delineated from the 4DCT images, i.e., Maximum IP(MIP), Average IP(AIP), and also Helical CT as references. This QA procedure was repeated daily, weekly, monthly, and annually to determine the necessary frequency.
Results: Both the Anzai and RPM systems showed good linearity throughout the time course. We report a baseline %volume to TV, namely MIP(96Β±3% of TV), AIP(95Β±3% of TV) and Helical(70Β±30% of TV) and testes consistency with the acquisition conditions of 4DCT throughout the time course, showing high reliability for both the ANZAI and RPM systems. The results suggest strong linearity of the ANZAI and RPM systems, with consistent ball volume markers recorded from MIP, and AIP.
Conclusion: We recommend implementing the 4DCT QA we proposed annually to ensure the accuracy of the respiratory motion external markers used in the 4DCT reconstruction.