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First MR-Guided Online Adaptive Patient Treatment in North America On An In-Room High Field (1.5 T) MRI Linac

S Vedam*, J Yang , C Fuller , C Chung , P Balter , B Lee , P Castillo , N Hughes , G Ungchusri , M McAleer , A Koong , J Herman , M Gillin , M Martel , J Wang , MD Anderson Cancer Center, Houston, TX


(Monday, 7/15/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 2

Purpose: Describe experience with the first MR-guided online adaptive patient treatment on an in-room high field (1.5 T) MRI Linac.

Methods: FDA approval for patient treatments on an in-room high field MRI Linac (Elekta Unity©, Elekta AB, Stockholm) was granted in Dec 2018. Following a rigorous acceptance testing/commissioning process, the first patient was treated in January 2019 for a secondary malignant neoplasm of cecum. Patient was pre-screened for MRI specific contraindications. An indexed MR table overlay was used at CT simulation to localize the target within the MR Linac co-ordinate space. 7 MV FFF IMRT Step and Shoot reference plan was generated, accounting for magnetic field effects on the dose distribution. Pre-treatment QA involved (i) Independent secondary MU verification (RadCalc, LifeLine Software Inc., Austin) and (ii) IMRT QA (ArcCheck-MR, Sun Nuclear Corporation, Melbourne FL). Patient was setup according to index location determined at simulation. Adaptation of original plan was based on rigid fusion of simulation CT to a T2 weighted pre-adaptation MR scan. Adapted plan MUs were verified with another independent secondary MU verification.

Results: Reference plan delivered 800 cGy in 1 fraction to the planned isocenter. Secondary MU verification indicated an overall difference of 3.2 % from original plan. Isocenter shifts (cm) between initial CT and pre-adaptation MRI were 1.8, 0.1, 0.3 along x, y and z axes respectively (no external in-room lasers). IMRT QA indicated a gamma value of 99.8 % @ 3%, 3 mm (%DD, DTA). Adaptive plan met all plan evaluation criteria. Post adaptation secondary MU verification indicated an overall plan difference of 6.6% from the original plan. Total in-room patient time was 53 minutes. Post treatment IMRT QA indicated a gamma value of 99.8% @ 3%, 3 mm (%DD, DTA).

Conclusion: First patient treatment on an in-room high field MR Linac system was completed successfully.


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