Quantification and Dosimetric Impact of Normal Organ Motion During Adaptive Radiation Therapy Plan Verification Using a 1.5 Tesla Magnetic Resonance Equipped Linear Accelerator (MR LINAC)

Abstract

Results: A total of 2278 SE and DE image frames were analyzed. DE imaging resulted in significantly improved tracking vs. SE on 884/2278 (38.8%) of image frames. In those frames, the average tracking error was 1.78 +/-2.02 mm vs. 2.21 +/-2.38 mm, for DE vs. SE imaging, respectively (P < 0.001). For 4/10 patients, the average reduction in tracking error with DE vs. SE tracking was > 0.7 mm. No correlation was observed between tumor volume/location and improved tracking accuracy with DE imaging. Additionally, the fraction of images that could not be tracked with SE was 91/2278 (4.0%). The addition of DE imaging decreased this number to 33/2278 (1.4%) (P < 0.001). Conclusion: This is the first prospective study to evaluate fast-kV switching DE imaging for MTT in a cohort of SBRT lung cancer patients. This study has demonstrated that by removal of overlapping bony anatomy, DE imaging increases tracking accuracy and decreases the number of images where tracking fails. Future work includes optimization of template parameters to further improve DE tracking accuracy.