Program Information
Real-Time Performance of the Elekta MR-Linac Clinical Prototype
M Glitzner*, P Woodhead , J Lagendijk , B Raaymakers , University Medical Center Utrecht, Utrecht, The Netherlands
Presentations
TU-FG-FS2-10 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: Four Seasons 2
Purpose: To determine the capability of the MR-linac to perform real-time motion compensation.
Methods: The latencies of imaging (I) and gating (II) of the MR-linac (Elekta AB, Stockholm,Sweden) clinical prototype were determined, by tracking a moving object with known motion trajectory using the on-line MRI. The motion was imposed using an in-house developed motion stage with programmable motion. The motion stage translated a phantom with sufficient MR-contrast in a sinusoidal manner (A=15mm, T=6s) and was programmed to return real-time position feedback. To obtain the imaging latency (I), multiple T1w sequences (α=6°, TE=2.3ms) with different imaging frequencies (1,2,3,4,5 Hz) were acquired. The object position in the MRI was then determined and compared to the real object position, obtaining the imaging latency as a function of image acquisition speed. The gating latency was determined as the time between real object position at the positive/negative gating threshold and the actual beam off/on, reported by the experimental real-time software employing a cross-correlation object tracking algorithm.
Results: The imaging latency (I) shows a linear dependency on the acquisition time Tacq. A linear fit over the 5 sampling points suggested a lag of 62ms + 0.48*Tacq . The offset of 62ms can be attributed to acquisition, reconstruction and transportation of the data, while the latter is the delay of the MRI-sampling process. The overall latency of the real-time gating loop is 407.6 ms, including real-time image processing and an average delay between a gating command and a confirmed gating state of 76 ms.
Conclusion: Using experimental software, the first experiments investigating the imaging and feedback performance of the MR-linac was performed. The timing figures show promising values for real-time applications. The experiments showed the relatively high contribution ofMR-image acquisition to the overall latency. Therefore, further research will be directed towards the acceleration of on-line MR-imaging.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by the SoRTS consortium, including the industry partners Elekta, Philips and Technolution.
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