title: Preliminary results on the feasibility of using ultrasound to monitor intrafractional motion during radiation therapy for pancreatic cancer.
abstract: OBJECTIVE
  Substantial intrafraction organ motion during radiation therapy (RT) for pancreatic cancer is well recognized as a major limiting factor for accurate delivery of RT. The aim of this work is to determine the feasibility of monitoring the intrafractional motion of the pancreas or surrounding structures using ultrasound for RT delivery.
  
  
  METHODS
  Transabdominal ultrasound (TAUS) and 4DCT data were acquired on ten pancreatic cancer patients during radiation therapy process in a prospective study. In addition, TAUS and MRI were collected for five healthy volunteers. The portal vein (PV) and the head of the pancreas (HP) along with other structures were contoured on these images. Volume changes, distance between the HP and PV, and motion difference between the HP and PV were measured to examine whether PV can be used as a motion surrogate for HP. TAUS images were acquired and processed using a research version of the Clarity autoscan ultrasound system (CAUS). Motion monitoring was performed with the ultrasound probe mounted on an arm fixed to the couch. Video segments of the monitoring sessions were captured.
  
  
  RESULTS
  On TAUS, PV is better visualized than HP. The measured mean volume deviation for all patients for the HP and PV was 1.4 and 0.6 ml, respectively. The distance between the HP and PV was close to a constant with 0.22 mm mean deviation throughout the ten breathing phases. The mean of the absolute motion difference for all patients was 1.7 ± 0.8 mm in LR, 1.5 ± 0.5 mm in AP, and 2.3 ± 0.7 mm in SI, suggesting that the PV is a good surrogate for HP motion estimation. By using this surrogate, the HP motion tracking using TAUS was demonstrated.
  
  
  CONCLUSIONS
  Large intrafractional organ motion due to respiratory and/or bowel motion is a limiting factor in administering curative radiation doses to pancreatic tumors. The authors investigate the use of real-time ultrasound to track pancreas motion. Due to the poor visibility of the pancreas head on an ultrasound image, the portal vein is identified as a surrogate. The authors have demonstrated the feasibility of tracking HP motion through the localization of the PV using TAUS. This will potentially allow real-time tracking of intrafractional motion to justify small PTV-margins and to account for unusual motions, thus, improving normal tissue sparing.
authors: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: Eenas A
authors: EA
authors: Omari
authors: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: Beth
authors: B
authors: Erickson
authors: Department of Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: Christopher
authors: C
authors: Ehlers
authors: Department of Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: Francisco
authors: F
authors: Quiroz
authors: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: George
authors: G
authors: Noid
authors: Elekta Ltd., Montreal, Québec H3A 2J5, Canada.
authors: David T
authors: DT
authors: Cooper
authors: Elekta Ltd., Montreal, Québec H3A 2J5, Canada.
authors: Martin
authors: M
authors: Lachaine
authors: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors: X Allen
authors: XA
authors: Li
mesh_terms: D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D009068:Movement; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided; D014463:Ultrasonography