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End-To-End Tests of a High-Field MR-Linac

X Chen*, E Paulson , E Ahunbay , P Prior , X Li , Froedtert Hospital and the Medical College of Wisconsin, Milwaukee, WI


(Wednesday, 8/1/2018) 4:30 PM - 6:00 PM

Room: Karl Dean Ballroom C

Purpose: The MR-Linac entire workflow including planning and delivery processes need to be fully tested, so called end-to-end test, before the system can be used for patient. This work reports the end-to-end tests for a pre-clinical MR-Linac system.

Methods: A pre-clinic MR-Linac consisting of a 1.5 T MRI and a 7 MV Linac along with the treatment planning system (TPS) and treatment services manager (TSM) are used in the tests. IGRT shift check was done using MR-MV alignment phantom. The daily MR images were rigidly registered with the reference images. The position shift needed in the TPS is compared to the original shift of the reference images. A series of RT plans, including static plans with rectangular field 5x10 cm² at different gantry angles and the IMRT QA plans for lung, liver, pancreas and prostate-bed patients, were generated in TPS. An adaptive plan was generated using daily MR images for the pancreas patient. The plans were then transferred into the TSM that controls the beam delivery. All the plans were delivered to a 3D diode detector array mounted on a QA platform which helps align the detector array. The repeatability of the alignment was checked with a MV phantom. The measured dose by detector array was compared with the dose generated in the TPS.

Results: The IGRT shift check showed that the accuracy of the shift is ≤ 0.5 mm in all direction. The uncertainty of the detector-array positioning with QA platform is within 1.0 mm. The agreements between the measured and planned dose distributions were all passed using gamma analysis with clinic criteria (3%/3mm/5%), especially for patient QA with high passing rates (~99%) .

Conclusion: The end-to-end tests verified the entire workflow of the MR-Linac system in term of its workflow throughput, geometric precision, dosimetry accuracy and delivery repeatability.


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