title: Evaluation of the dose perturbation around gold and steel fiducial markers in a medical linac through Geant4 Monte Carlo simulation.
abstract: OBJECTIVE
  Purpose of this work was to study the dose perturbation within the target volume of a external MV radiation therapy when using metal fiducials.
  
  
  METHODS
  We developed a Monte Carlo simulation in Geant4 of a cylindrical fiducial made either of gold or of steel and simulated the photon irradiation beam originating from a medical Linac operating at 6, 10 or 15 MV. For each energy, two different irradiation schemes were simulated: a single 5 × 5-cm square field in the -x direction, and five 5 × 5-cm fields at 0°, 80°, 165°, 195° and 280°.
  
  
  RESULTS
  In a single beam irradiation scheme, we observed a dose reduction behind fiducials varying from -20% for gold at 6 MV to -5% for steel at 15 MV, and a dose increment in front of the fiducial ranging from +33% for gold at 15 MV to +10% for steel at 6 MV. When five beams were employed, a dose increment ranging from +28% to +46% has been found around gold. Around a steel fiducial, an average increment of +17% was found, irrespective of the photon energy.
  
  
  CONCLUSIONS
  When using a single beam, the decrement of dose behind both steel and gold markers increases with the photon energy. This effect vanishes when a multifield treatment is delivered; in this instance there is a dose increment around fiducials, according to both fiducial material and photon energy, with lower values for steel and 6 MV. This energy represents the best choice when fiducial markers are present inside the irradiated volume.
authors.affiliation: Department of Biomedical Sciences and of Morphologic and Functional Imaging, University of Messina, Messina, Italy Radiotherapy Unit, University Hospital "G. Martino", Messina, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Pontoriero
authors.affiliation: Department of Biomedical Sciences and of Morphologic and Functional Imaging, University of Messina, Messina, Italy.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Amato
authors.affiliation: Radiotherapy Unit, University Hospital "G. Martino", Messina, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Iatí
authors.affiliation: Department of Biomedical Sciences and of Morphologic and Functional Imaging, University of Messina, Messina, Italy Radiotherapy Unit, University Hospital "G. Martino", Messina, Italy.
authors.forename: Costantino
authors.initials: C
authors.lastname: De Renzis
authors.affiliation: Department of Biomedical Sciences and of Morphologic and Functional Imaging, University of Messina, Messina, Italy Radiotherapy Unit, University Hospital "G. Martino", Messina, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Pergolizzi
mesh_terms: D003198:Computer Simulation; D057918:Fiducial Markers; D006046:Gold / Q000737:chemistry*; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013232:Steel / Q000737:chemistry*
chemical_list: D013232:Steel; D006046:Gold
keywords: Monte Carlo; Radiotherapy; dose; fiducial marker x-rays