title: Energy and field size dependence of a silicon diode designed for small-field dosimetry.
abstract: OBJECTIVE
  To investigate the energy dependence/spectral sensitivity of silicon diodes designed for small-field dosimetry and obtain response factors (RFs) for arbitrary photon spectra using Monte Carlo (MC) simulations.
  
  
  METHODS
  The EGSnrc user-code DOSRZnrc was used to calculate the dose deposition in water and in the active volume of a stereotactic diode field detector (SFD). Then, the RFs of the SFD were calculated for several circular field sizes and energies at 5 cm depth in water. Several low-energy photon spectra (mean energy 55 to 200 keV), as well as Co-60 radiation (mean energy 1.25 MeV) and a 6 MV Elekta Synergy beam (mean energy 2.9 MeV), in 10 × 10 cm2field size were used to validate the MC calculations, using a simple beam model. The RFs of the SFD detector for a 6 MV Elekta Synergy linac photon beam in different field sizes were calculated. These were also measured with EBT3 Gafchromic film and the SFD detector.
  
  
  RESULTS
  For the reference field size, differences between measured and calculated RFs were less than 5% at mean energies below 1 MeV and less than 1% at energies above 1 MeV. The calculated RFs for a 6 MV Elekta Synergy linac photon beam as a function of different field sizes showed a good agreement between the measurements and previously reported results. This agreement was within 2% for all considered field sizes.
  
  
  CONCLUSIONS
  While at high photon energies, the change of response of the SFD is marginal, whereas it is extreme at low energies. Therefore, it is desirable to benchmark response calculations also in the low-energy domain. Our results, with a simple beam model and geometry, indicate that a validation of the simulations by experimental results is achievable. The present work provides a comprehensive table that can be used to calculate SFD detector response factors depending on both, field size and photon energy.
authors.affiliation: Department of Medical Physics, Faculty of Medicine, Kurdistan University of Medical Sciences, Sanandaj, Iran.
authors.forename: Mehran
authors.initials: M
authors.lastname: Yarahmadi
authors.affiliation: Department of Radiation Oncology, University of Würzburg, Josef-Schneider-Strasse 11, 97080, Würzburg, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Wegener
authors.affiliation: Department of Radiation Oncology, University of Würzburg, Josef-Schneider-Strasse 11, 97080, Würzburg, Germany.
authors.forename: Otto A
authors.initials: OA
authors.lastname: Sauer
mesh_terms: D009010:Monte Carlo Method; D010315:Particle Accelerators; D017785:Photons; D011874:Radiometry; D012825:Silicon
chemical_list: D012825:Silicon
keywords: Monte Carlo; diodes; response factor; small fields