SU-F-303-10: Impact of Visual Biofeedback On Respiratory Reproducibility in 4DMRI

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Purpose: Precise radiation therapy (RT) for abdominal lesions is complicated by respiratory motion and suboptimal soft tissue contrast in 4DCT. 4DMRI offers improved contrast. However, long scan times and irregular breathing patterns can be limiting. To address this, we introduced visual biofeedback (VBF) into 4DMRI. Methods: Eight healthy volunteers were consented to an IRB-approved protocol. Prospective respiratory-triggered, T2-weighted coronal 4DMRIs were acquired on an open 1.0T MR- SIM. VBF was integrated using an MR-compatible interactive breath-hold control system. Subjects visually monitored their breathing patterns to stay within pre-determined tolerances. 4DMRIs were acquired with and without VBF for 2–8 phase acquisitions. Normalized respiratory waveforms were evaluated for scan time, duty cycle (programmed/acquisition time), breathing period, end-inhale (EI) amplitude, and breathing variability (coefficient of variation, EI-COV). B-spline-based deformable image registration propagated contours from end-exhale (EE) to EI phases. Respiration-induced liver motion was calculated via centroid analysis and compared. Results: Incorporating VBF reduced 2-phase acquisition time (4.7±0.6 and 5.6±1.4 minutes with and without VBF, respectively) while reducing the amplitude EI-COV by 53.0±8.1%. On average, incorporating VBF reduced 8-phase 4DMRI acquisition times by 1.7±1.2 minutes and EI-COVs by 46.0±15.8%. Using VBF yielded higher duty cycles than free breathing (34.7% versus 28.3%, respectively). 4DMRI acquisition time was reduced for the cohort with VBF despite breathing rate remaining similar (10.5±4.0 with vs. 10.6±3.3 BPM without). Respiratory waveforms showed higher EI amplitude with VBF (0.84±0.05 a.u.) as compared to 0.72±0.06 a.u. without. This translated to differences in liver excursions, where superior-inferior, anterior-posterior, and left-right EE-EI displacements were 14.3±3.6, 4.8±2.1, and 1.6±1.0 mm, respectively, with VBF compared to 13.0±6.2, 3.8±2.4, and 1.2±1.4 mm without. Conclusion: Incorporating VBF system into 4DMRI substantially reduced acquisition time and breathing variability. While VBF reduced liver motion variability, differences in excursion were observed, suggesting that implementation will be required throughout the RT workflow. Research supported in part by a grant from Philips HealthCare (Best, Netherlands) and an equipment evaluation agreement with MedSpira.

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