Towards clinical implementation of T2-weighted cine imaging for intrafraction drift correction workflows on the 1.5 Tesla magnetic resonance-linear accelerator

Background and purpose: In magnetic resonance–linear accelerator (MR-Linac) treatments, balanced Turbo Field Echo (bTFE) cine imaging is used to monitor and correct intrafraction motion but provides limited contrast and is prone to artifacts. This study evaluates a T2-weighted Turbo Spin Echo (T2-TSE) cine sequence for intrafraction drift correction in pelvic targets and compares its performance with the bTFE-cine. Materials and methods: During 86 fractions in 52 patients with pelvic tumors, the standard bTFE-cine and the T2-TSE-cine images were acquired interleaved coronal and sagittal on the MR-Linac. Pre- and post-treatment T2-weighted 3D images were registered. Intrafraction motion, deviations between 3D-3D and 3D-2D registration, and jitter were compared. Visual grading scores and acoustic noise levels were assessed in both sequences. Results: The bTFE-cine shows in 26 cases > 1 mm between the 3D-3D and 3D-2D registration compared to 6 cases for the T2-TSE-cine in all directions, however these differences were not statistically significant. The jitter was higher for the bTFE-cine in prostate cases compared to T2-TSE-cine, but comparable or less for rectum and pelvic lymph node metastatic cases. The visual assessment indicates a high preference for the T2-TSE-cine regarding target, organs at risk (OAR) visualization and in terms of artifacts. The equivalent sound levels for the bTFE-cine and T2-TSE-cine were 110.7 and 100.1 dB(A), respectively. Conclusion: This study shows comparable tracking results, higher visual grading scores and lower acoustic noise levels of the T2-TSE-cine sequence over the bTFE-cine used for intrafraction drift correction workflows of pelvic targets on the MR-Linac.