Purpose: To determine if a simple MRI compatible ultrasound device can uniquely identify anatomical changes that would make a clinical impact on dose-escalated pancreatic cancer radiotherapy.
Methods: Three healthy subjects were enrolled in this IRB approved study. The ultrasound system consisted of three, single element 1 MHz ultrasound transducers fixed to the abdomen, anterior to the pancreas. Simultaneous ultrasound data collection and MR imaging were performed in a 3T scanner under breath-hold conditions. After the first MR scan, the subject drank 8 oz of water to induce organ-filling. Two more scans were performed: one started one-minute after the water intake, the final started 10 minutes later. The experiment was repeated 2 weeks later. OARs were contoured and a simulated GTV was drawn by an experienced radiation oncologist. Dose-escalated two-field VMAT plans were constructed on initial phase MR images and then the same plan was registered and delivered using the MR images after the anatomical changes were induced. HU inside the body was set to 0. V30, V35, and V40 of stomach and duodenum were evaluated and compared with differences measured by the ultrasound system.
Results: Compared to before water intake, the dosimetric parameters for stomach significantly increased shortly after water intake (1.05Â±0.85 cc vs. 5.41Â±2.47 cc, 0.30Â±0.26 cc vs. 2.77Â±1.39 cc, and 0.04Â±0.05 cc vs. 1.46Â±0.90 cc for the V30, V35, and V40, respectively) and failed to fulfill the dose constraints. There was no significant difference between before and 10 minutes after water intake. Anatomical changes detected by the ultrasound sensors showed similar trend with the dosimetric parameters for stomach.
Conclusion: Our results indicate that the ultrasound sensors can identify dosimetrically relevant anatomical changes for pancreas cancer radiotherapy. This suggests that the ultrasound system can potentially predict when soft-tissue anatomical changes might prompt an adaptation of the radiotherapy 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.