title: Experimental evaluation of x-ray acoustic computed tomography for radiotherapy dosimetry applications.
abstract: OBJECTIVE
  The aim of this work was to experimentally demonstrate the feasibility of x-ray acoustic computed tomography (XACT) as a dosimetry tool in a clinical radiotherapy environment.
  
  
  METHODS
  The acoustic waves induced following a single pulse of linear accelerator irradiation in a water tank were detected with an immersion ultrasound transducer. By rotating the collimator and keeping the transducer stationary, acoustic signals at varying angles surrounding the field were detected and reconstructed to form an XACT image. Simulated XACT images were obtained using a previously developed simulation workflow. Profiles extracted from experimental and simulated XACT images were compared to profiles measured with an ion chamber. A variety of radiation field sizes and shapes were investigated.
  
  
  RESULTS
  XACT images resembling the geometry of the delivered radiation field were obtained for fields ranging from simple squares to more complex shapes. When comparing profiles extracted from simulated and experimental XACT images of a 4 cm × 4 cm field, 97% of points were found to pass a 3%/3 mm gamma test. Agreement between simulated and experimental XACT images worsened when comparing fields with fine details. Profiles extracted from experimental XACT images were compared to profiles obtained through clinical ion chamber measurements, confirming that the intensity of XACT images is related to deposited radiation dose. Seventy-seven percent of the points in a profile extracted from an experimental XACT image of a 4 cm × 4 cm field passed a 7%/4 mm gamma test when compared to an ion chamber measured profile. In a complicated puzzle-piece shaped field, 86% of the points in an XACT extracted profile passed a 7%/4 mm gamma test.
  
  
  CONCLUSIONS
  XACT images with intensity related to the spatial distribution of deposited dose in a water tank were formed for a variety of field sizes and shapes. XACT has the potential to be a useful tool for absolute, relative and in vivo dosimetry.
authors.affiliation: Department of Physics and Medical Physics Unit, McGill University, Cedars Cancer Centre, Montreal, QC, Canada, H4A 3J1.
authors.forename: Susannah
authors.initials: S
authors.lastname: Hickling
authors.affiliation: Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Lei
authors.affiliation: Medical Physics Unit, McGill University Health Centre, Cedars Cancer Centre, Montreal, QC, H4A 3J1, Canada.
authors.forename: Maritza
authors.initials: M
authors.lastname: Hobson
authors.affiliation: Medical Physics Unit, McGill University Health Centre, Cedars Cancer Centre, Montreal, QC, H4A 3J1, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Léger
authors.affiliation: Departments of Radiology and Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109-0600, USA.
authors.forename: Xueding
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 48103-4943, USA.
authors.forename: Issam
authors.initials: I
authors.lastname: El Naqa
mesh_terms: D000162:Acoustics; D007091:Image Processing, Computer-Assisted; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: X-ray acoustic computed tomography; radiation dosimetry; thermoacoustics; ultrasonics