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Direct Tumor Visualization in 0.35T MRgRT for Tumor Motion Control in Free Breathing

T Kim*, B Lewis, A Price, T Mazur, H Gach, J Park, B Cai, E Wittland, L Henke, H Kim, S Mutic, O Green, Washington University School of Medicine, St. Louis, MO


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: present the feasibility of displaying direct tumor visualization in 0.35T MRI-guided radiotherapy (MRgRT) to patients for improving tumor motion control under free breathing.

Methods: provided direct tumor visualization to patients by displaying cine MR images acquired in real-time on an MRI-compatible display system in 0.35T MRgRT. Tumor visualization was tailored to include anatomical images with both a target boundary and an auto-segmented target contour overlaid onto the images. In addition, a beam status indicator communicated to the patient whether the beam was on or off during gated delivery. Six abdominal cancer patients (total 37 fractions) participated in clinical evaluation of the visual guidance (VG) system. These treatments were compared to six abdominal cancer patients (total 33 fractions) treated without VG in terms of duty cycle and distance traveled beyond the target boundary in the superior-inferior direction. In addition, treatment time was analyzed to assess the efficacy of the system.

Results: direct tumor visualization system was successfully developed and clinically implemented in our clinic. The distal edge of the tumor traveled more than 3mm in the SI direction on 31.8% and 36.4% of cine images with and without VG. The maximum SI motion was 28mm and 48mm with and without VG, respectively. Duty cycle taken as the number of frames the target contour was completely inside the boundary was 76% and 77% with and without VG. The average ± SD of beam-on time with and without VG was 48.0±21.2% and 43.9±15.3% of the treatment time.

Conclusion: demonstrated the clinical feasibility of presenting direct tumor visualization to patients in MRgRT. VG improved tumor motion control in terms of efficiency and reproducibility under free breathing, reducing the maximum extent of tumor motion, and reducing treatment time. The proposed system and associated clinical workflow can be easily adapted for any MRgRT platform.

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