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Elekta Unity MR-Linac Daily Automated End-To-End Quality Control

V Malkov*, J Winter, D Letourneau, The Princess Margaret Cancer Centre, Toronto, ON, Canada


(Sunday, 7/12/2020) 3:30 PM - 4:30 PM [Eastern Time (GMT-4)]

Room: Track 3


To develop a quality control (QC) test to evaluate the Elekta Unity’s end-to-end (E2E) MR-guided plan adaptation and delivery performance using automated analysis.


Our E2E QC workflow employed the vendor supplied MR-to-MV phantom, which contains seven MR and MV detectable fiducials. To test the MR-guided online plan adaptation, we generated a 3D-CRT plan composed of four cardinal-angle radiation beams targeting two fiducials on a reference CT scan. During the daily QC, the phantom was offset from the reference plan position by shifting the couch-index bar in the superior-inferior direction and by shifting the reference plan isocenter in the lateral and vertical directions. We then placed a separate index bar containing an x-ray marker on the couch to evaluate positioning reproducibility. Plan adaptation was performed on a T1-weighted MR image that was rigidly fused with the planning CT. We generate a plan-of-the-day using the Adapt to Position workflow, delivered the beams and collected MV images. We exported the RT plan, MR image and MV images for offline automated processing with our in-house developed Python tool, which compares the phantom and plan isocenter shifts, planned and observed radiation field centers, couch position, and MR-to-MV shift.


We analyzed 76 daily test instances. Couch positioning reproducibility was within 0.5 mm. Phantom and plan isocenter shifts were within ±0.5 mm in the lateral and vertical directions and ±1 mm in the longitudinal direction. We found the increased longitudinal variation was associated with the 0.9 mm MR-to-CT registration variability. Planned and observed radiation field centers were within ±0.6 mm in the jaw and MLC directions. Calculated MR-to-MV isocenter shifts agreed to within 0.1 mm of the vendor-provided test results.


We implemented a novel automated and sensitive E2E QC workflow capable of efficiently and accurately integrating numerous daily QC elements.


Not Applicable / None Entered.


Not Applicable / None Entered.

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