SU‐D‐210‐06: Feasibility for Monitoring the Head of the Pancreas Motion Through a Surrogate Using Ultrasound During Radiation Therapy Delivery

Abstract

Purpose: Substantial target motion during the delivery of radiation therapy (RT) for pancreatic cancer is well recognized as a major limiting factor on RT effectiveness. The aim of this work is to monitor intra‐fractional motion of the pancreas using ultrasound during RT delivery. Methods: Transabdominal Ultrasound B‐mode images were collected from 5 volunteers using a research version of the Clarity Autoscan System (Elekta). The autoscan transducer with center frequency of 5 MHz was utilized for the scans. Imaging parameters were adjusted to acquire images at the desired depth with good contrast and a wide sweep angle. Since well‐defined boundaries of the pancreas can be difficult to find on ultrasound B‐mode images, the portal vein was selected as a surrogate for motion estimation of the head of the pancreas. The selection was due to its anatomical location posterior to the neck of the pancreas and close proximity to the pancreas head. The portal vein was contoured on the ultrasound images acquired during simulation using the Clarity Research AFC Workstation software. Volunteers were set up in a similar manner to the simulation for their monitoring session and the ultrasound transducer was mounted on an arm fixed to the couch. A video segment of the portal vein motion was captured. Results: The portal vein was visualized and segmented. Successful monitoring sessions of the portal vein were observed. In addition, our results showed that the ultrasound transducer itself reduces breathing related motion. This is analogous to the use of a compression plate to suppress respiration motion during thorax or abdominal irradiation. Conclusion: We demonstrate the feasibility of tracking the pancreas through the localization of the portal vein using abdominal ultrasound. This will allow for real‐time tracking of the intra‐fractional motion to justify PTV‐margin and to account for unusual motions, thus, improving normal tissue sparing. This research was funding in part by Elekta Inc.

Review of ultrasound image guidance in external beam radiotherapy part II: intra-fraction motion management and novel applications

“…The pancreas can be difficult to visualise with an abdominal US transducer. Omari et al (2015) have assessed the feasibility of using portal vein motion, visualised using Elekta Clarity ™ , as a surrogate for pancreatic motion. US has not been used for intra-fraction motion estimation A kernel or reference ROI is selected in an US image (acquisition 1) and the pattern that best matches this is located in a subsequent image (acquisition 2) by computing a similarity metric, such as the normalised cross-correlation coefficient, at many test locations within a larger search region.…”