H Jassar¹*, A Tai¹, X Chen¹, E Paulson¹, F Lathuiliere², S Beriault², F Hebert², L Savard², D Cooper², S Cloake², X Li¹, (1) Medical College of Wisconsin, Milwaukee, WI, USA,(2) Elekta, Stockholm, Sweden

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  H Jassar

SU-H330-IePD-F6-5 (Sunday, 7/10/2022) 3:30 PM - 4:00 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 6

Purpose: The accuracy of real-time motion monitoring (RTMM) using cine MRI on MR-Linac can be significantly affected by through-plane motion (TPM) of the target. This work investigates the feasibility of using deep-inspiration-breath-hold (DIBH) to address TPM in RTMM based on orthogonal cine MRI for the abdominal targets.

Methods: RTMM was performed using a software tool developed to measure real-time target motion based on template registration between real-time orthogonal cine MRI and the baseline 3D-MRI. RTMM was evaluated using healthy volunteer MRI data with the pancreas-head as RTMM target acquired on a 1.5T MR-Linac in two separate breathing modes: (1) baseline 3D mid-position images derived from 4D-MRI and real-time T2/T1-weighted bFFE orthogonal cine MRI under free-breathing, and (2) 3D T1-weighted and orthogonal cine images under DIBH. The cine images were acquired with a temporal resolution of 0.2s interleaved between coronal and sagittal orientations. A 2D-template was created for each breathing mode in both orientations using the cine data acquired over the first 12s, followed by a rigid registration to the corresponding 3D-MRI using the target mask. Manually delineated ground-truth contours on cine frames were used to evaluate RTMM accuracy under DIBH vs free-breathing using the standard deviation of the error (SDE) to compare the center-of-mass position of the ground-truth and the monitored motion. Maximum target motion (MTM) was measured on 4D-MRI.

Results: Under free-breathing, the MTMs were 17, 8, and 8mm and the mean RTMM SDE values were 7.1, 1.4, and 3.1mm in superior-inferior (SI), left-right, and anterior-posterior (AP) directions, respectively. The higher SDE in SI and AP directions was due to the large TPM of the target. Under DIBH, the SDE was < 2mm.

Conclusion: We have demonstrated the feasibility of using DIBH to reduce TPM, substantially improving accuracy of RTMM of abdominal targets using orthogonal cine MRI on MR-Linac.

Funding Support, Disclosures, and Conflict of Interest: Funding Support By Elekta

Keywords

MRI, Image-guided Therapy

Taxonomy

IM/TH- MRI in Radiation Therapy: Development (new technology and techniques)

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