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Inter-Machine Comparison of Volumetric Intensity Modulated Arc Therapy (VIMAT) Delivery Based On Trajectory Log Analysis

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K Chan

Kenny S. K. Chan1*, Taskie S. K. Lau1, Louis K. Y. Lee1, Michael K. M. Kam1, Brian K. H. Yu1, Anthony T. C. Chan1, 2, (1) Department of Clinical Oncology, Prince of Wales Hospital, Hong Kong SAR, China (2) State Key Laboratories of Southern China, Sir YK Pao Cancer Center, Department of Clinical Oncology, The Chinese University of Hong Kong, Hong Kong SAR, China

SU-C-137-3 Sunday 1:00PM - 1:55PM Room: 137

To compare the machine performance including the MU delivery, Gantry Angle trajectory and Multi-Leaf Collimator (MLC) leaf motion of RapidArc delivery based on trajectory log analysis.

Five RapidArc cases were selected for the study. Each case was delivered at Varian Unique, iX23 and TrueBeam Linear Accelerator (LINAC) system. The system log files were obtained after their corresponding field measurements. During measurements, an independent inclinometer was mounted on the machine to verify the gantry rotation dynamically. In-house software was developed to extract and reconstruct the data into trajectory plots for comparison. Another in-house software was used to compare the Integrated Transient Fluence Map (ITFM) to check the accuracy of MLC leaf position and dose index.

For all selected cases delivered in the Unique, iX23 and TrueBeam system, the typical deviations of gantry angle and MU were found to be (0.6+/-0.1°, 0.0+/-0.2 MU), (0.4+/-0.1°, 0.0+/-0.1 MU) and (0.0+/-0.1°, 0.0+/-0.0 MU) respectively. Their angular trajectories of the independent inclinometer agreed well with the digital readout of gantry angle. The trajectory plots of dose index against gantry angle were in a good agreement with their plans. The reconstructed ITFM showed no observable difference when compared with the planned one, and their typical correlation coefficients were very close to unity. This indicated accurate MU delivery and MLC leaf position during the delivery. The higher accuracy of RapidArc delivery was achieved by the digital control system (TrueBeam).

The analysis of trajectory log is presented in the form of trajectory plot and ITFM, which are the powerful tools to check the machine performance of RapidArc delivery. For the inter-machine comparison, the integrated and digital control LINAC (TrueBeam) delivers the RapidArc treatment more precisely compared to its counterparts (iX23 and Unique).

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