Report of Image Distortion Based On Five Consecutive Years of Annual QA On Six MRI Scanners Used for Radiation Therapy
L Lu*, X Yang, B Raterman, X Jiang, M Meineke, D Hintenlang, N Gupta, Ohio State Univ, Columbus, OH
Presentations
PO-GePV-P-49 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To determine MRI image distortion based on five consecutive years of annual measurements on six MRI scanners used for radiation therapy.
Methods: We used a commercial MRI image phantom MRID3D to perform annual image distortion checks and monitor the stability of the distortion over a period of five years from 2016 to 2020 for six 1.5T and 3T MRI scanners that provided images for the treatment planning of radiation therapy. The phantom was scanned on these MRI machines with 1 mm image slice thickness to acquire 3D images by following the imaging protocol of Gamma Knife and Linac-based SBRT/SRS. For each imaging scan the phantom was aligned to its geometric center using the MRI’s lasers and the localizer. Using the MRID3D software we investigated: (1) the magnitude of the image distortion; (2) the dependence of distortion magnitude on the distance from the imaging isocenter; (3) the difference in distortion magnitude for 1.5T and 3T machines; and (4) the stability of distortion across the five-year period.
Results: The image distortion magnitude depended on the distance from the imaging isocenter. For most MRI scanners the distortion magnitude was under 1 mm when within 10 cm of the isocenter. The magnitude increased with increasing distance from the isocenter and could reach 2 mm at the distance of 15 cm. In general, a 3T machine had worse distortion than that of a 1.5T machine but the distortion could still be less than 1 mm when the distance from the isocenter was less than 10 cm. Slight fluctuation in distortion was observed during 5 years.
Conclusion: MRI image distortion varies for machines and manufacturers. It depends on the distance from the imaging isocenter. Additional margin due to MRI image distortion needs to be accounted for during treatment planning, especially for Gamma Knife or SRS/SBRT.
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