title: Radiation exposure to patients from image guidance procedures and techniques to reduce the imaging dose.
abstract: OBJECTIVE
  To compare imaging doses from MV images, kV radiographs, and kV-CBCT and describe methods to reduce the dose to patient's organs using existing on-board imaging devices.
  
  
  METHODS
  Monte Carlo techniques were used to simulate kV X-ray sources. The kV image doses to a variety of patient anatomies were calculated by using the simulated realistic sources to deposit dose in patient CT images. For MV imaging, the doses for the same patients were calculated using a commercial treatment planning system.
  
  
  RESULTS
  Portal imaging results in the largest dose to anatomic structures, followed by Varian OBI CBCT, Varian TrueBeam CBCT and then kV radiographs. The imaging doses for the 50% volume from the DVHs, D50, to the eyes for representative head images are 4.3-4.8cGy; 0.05-0.06cGy; 0.04-0.05cGy; and, 0.12cGy; D50 to the bladder for representative pelvis images are 3.3cGy; 1.6cGy; 1.0cGy; and, 0.07cGy; while D50 to the heart for representative thorax images are 3.5cGy; 0.42cGy; 0.2cGy; and, 0.07cGy; when using portal imaging, OBI kV-CBCT scans, TrueBeam kV-CBCT scans and kV radiographs, respectively. The orientation of the kV beam can affect organ dose. For example, D50 to the eyes can be reduced from 0.12cGy using AP and right lateral radiographs to 0.008-0.017cGy when using PA and right lateral radiographs. In addition, organ exposures can be further reduced to 15-70% of their original values with the use of a full-fan, bow-tie filter for kV radiographs. In contrast, organ doses increase by a factor of ∼2-4 if bow-tie filters are not used during kV-CBCT acquisitions.
  
  
  CONCLUSIONS
  Current on-board kV imaging devices result in much lower imaging doses compared to MV imagers even taking into account of higher bone dose from kV X-rays. And a variety of approaches are available to significantly reduce the image doses.
authors.affiliation: Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville 37232-5671, USA. george.ding@vanderbilt.edu
authors.forename: George X
authors.initials: GX
authors.lastname: Ding
authors.forename: Peter
authors.initials: P
authors.lastname: Munro
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D009010:Monte Carlo Method; D010388:Pelvis / Q000528:radiation effects; D011829:Radiation Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D013909:Thorax / Q000528:radiation effects
keywords: Imaging dose reduction techniques; MV imaging dose; kV-CBCT dose; kV-CBCT in TrueBeam; kV-radiograph dose