Room: AAPM ePoster Library
Purpose: high-soft tissue contrast MRI from MR-Linac offers the best opportunity for accurate motion tracking during radiation therapy delivery. However, MRI intensity and contrast, particularly in abdomen, can be different from day to day due to the changes in patient set-up and anatomy, resulting in daily variations in motion detection. This work aims to mitigate this complication by registering real-time cine MRI with daily patient-specific template images for abdominal target tracking.
Methods: approach consists of three steps, (1) acquiring cine and 3D MRIs immediately prior to treatment delivery, (2) creating a 2D template image on each tracking plane based on the cine and 3D MRIs, and (3) measuring motion on a plane by registering real-time cine MRI with the template image. Comparing to the conventional method where real-time cine is registered directly to 2D slices from the 3D MRI, the new approach eliminates daily variations in the 2D and 3D MRIs. The approach was tested using the abdominal MRIs collected on a 1.5T MR-Linac for 20 cases of healthy volunteers. Tracking accuracy is defined as the standard deviation of the error.
Results: to the conventional method where the tracking accuracy was < 3 mm in superior-inferior direction for 11/20 cases and > 5 mm for 5/20, the new approach showed improvement to 17/20 and 0/20, respectively. On average, the accuracy improved by 0.4 mm (19%), 1.1 mm (49%), and 2.2 mm (54%) in left-right, anterior-posterior, and superior-inferior directions, respectively. Similarly, there is an improvement to the 90% error range by 15, 45, and 53%. Overall accuracy of the proposed approach was below 2.2 mm.
Conclusion: abdominal organ motion tracking on MR-Linac is improved by optimized registration of real-time cine MRI with daily online-created patient-specific template images.
Funding Support, Disclosures, and Conflict of Interest: FL, SB, FH, DC, and ML are employees of Elekta, Ltd. This work is supported by Elekta AB.
Not Applicable / None Entered.
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined- IGRT and tracking