title: Adaptive motion mapping in pancreatic SBRT patients using Fourier transforms.
abstract: OBJECTIVE
  Recent studies suggest that 4DCT is unable to accurately measure respiratory-induced pancreatic tumor motion. In this work, we assessed the daily motion of pancreatic tumors treated with SBRT, and developed adaptive strategies to predict and account for this motion.
  
  
  METHODS
  The daily motion trajectory of pancreatic tumors during CBCT acquisition was calculated using a model which reconstructs the instantaneous 3D position in each 2D CBCT projection image. We developed a metric (termed "Spectral Coherence," SC) based on the Fourier frequency spectrum of motion in the SI direction, and analyzed the ability of SC to predict motion-based errors and classify patients according to motion characteristics.
  
  
  RESULTS
  The amplitude of daily motion exceeded the predictions of pre-treatment 4DCT imaging by an average of 3.0mm, 2.3mm, and 3.5mm in the AP/LR/SI directions. SC was correlated with daily motion differences and tumor dose coverage. In a simulated adaptive protocol, target margins were adjusted based on SC, resulting in significant increases in mean target D95, D99, and minimum dose.
  
  
  CONCLUSIONS
  Our Fourier-based approach differentiates between consistent and inconsistent motion characteristics of respiration and correlates with daily motion deviations from pre-treatment 4DCT. The feasibility of an SC-based adaptive protocol was demonstrated, and this patient-specific respiratory information was used to improve target dosimetry by expanding coverage in inconsistent breathers while shrinking treatment volumes in consistent breathers.
authors.affiliation: Department of Radiation Oncology, University of Colorado School of Medicine, United States. Electronic address: bernard.jones@ucdenver.edu.
authors.forename: Bernard L
authors.initials: BL
authors.lastname: Jones
authors.affiliation: Department of Radiation Oncology, University of Colorado School of Medicine, United States.
authors.forename: Tracey
authors.initials: T
authors.lastname: Schefter
authors.affiliation: Department of Radiation Oncology, University of Colorado School of Medicine, United States.
authors.forename: Moyed
authors.initials: M
authors.lastname: Miften
mesh_terms: D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009038:Motion; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods
keywords: Motion; Pancreas; Physics; SBRT