Purpose: To validate the use of ultrasound-based MRI compatible, â€˜organ configuration motionâ€™ (OCM) sensors, to detect the type of soft-tissue anatomical changes important toward accurate pancreatic cancer radiation therapy.
Methods: Three healthy subjects were enrolled in this IRB approved study. The subjects were imaged by MRI with 3 OCM sensors fixed to the anterior abdominal surface. The OCM signals were acquired simultaneously with three separate groups of 5 breath-hold MR scans. After the first group of scans, the subject consumed 8 oz of water to induce organ-filling and peristalsis. The next group of scans started 1 minute after water intake, followed by a ten-minute pause, and then the final group of scans was performed. The experiment was repeated 2 weeks later. All MR time frames were non-rigidly registered to the first frame, and a region of interest (ROI) was drawn around the stomach, duodenum, and pancreas. The average magnitude of the deformation vector field (DVF) was computed in the ROI. The magnitude of the OCM signals was computed, then averaged over the time period that corresponds to each group of MRI scans. The mean squared difference between the baseline and each breath-hold was computed.
Results: For both mean squared difference in OCM and the average magnitude of the MRI DVF, mean values increased considerably just after water consumption (p<0.0001), and then slightly decreased 10 minutes afterward. The drop from the second to the third time point was statistically significant (OCM: p=0.0170, MRI: p=0.00005). There was a moderate correlation between the mean difference in OCM and MRI (RÂ²=0.500).
Conclusion: Results of our study showed that OCM signal correlates with soft-tissue anatomical changes caused by organ-filling observed in MRI. These results indicate that OCM sensors can potentially predict when soft-tissue anatomical changes might prompt an adaptation of the radiation therapy treatment plan.
Funding Support, Disclosures, and Conflict of Interest: J. Kwon acknowledges support from a Research Fellowship of the Japanese Society for the Promotion of Science.