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