title: Extraction of depth-dependent perturbation factors for silicon diodes using a plastic scintillation detector.
abstract: OBJECTIVE
  This work presents the experimental extraction of the perturbation factor in megavoltage electron beams for three models of silicon diodes (IBA Dosimetry, EFD and SFD, and the PTW 60012 unshielded) using a plastic scintillation detector (PSD).
  
  
  METHODS
  The authors used a single scanning PSD mounted on a high-precision scanning tank to measure depth-dose curves in 6-, 12-, and 18-MeV clinical electron beams. They also measured depth-dose curves using the IBA Dosimetry, EFD and SFD, and the PTW 60012 unshielded diodes. The authors used the depth-dose curves measured with the PSD as a perturbation-free reference to extract the perturbation factors of the diodes.
  
  
  RESULTS
  The authors found that the perturbation factors for the diodes increased substantially with depth, especially for low-energy electron beams. The experimental results show the same trend as published Monte Carlo simulation results for the EFD diode; however, the perturbations measured experimentally were greater. They found that using an effective point of measurement (EPOM) placed slightly away from the source reduced the variation of perturbation factors with depth and that the optimal EPOM appears to be energy dependent.
  
  
  CONCLUSIONS
  The manufacturer recommended EPOM appears to be incorrect at low electron energy (6 MeV). In addition, the perturbation factors for diodes may be greater than predicted by Monte Carlo simulations.
authors: Département de Radio-Oncologie, Centre hospitalier de l'Université de Montréal , Québec, Canada. frederic.lacroix.chum@sss.gouv.qc.ca
authors: Frederic
authors: F
authors: Lacroix
authors: Mathieu
authors: M
authors: Guillot
authors: Malcolm
authors: M
authors: McEwen
authors: Luc
authors: L
authors: Gingras
authors: Luc
authors: L
authors: Beaulieu
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D006801:Humans; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D011882:Radiotherapy, High-Energy / Q000379:methods; D015203:Reproducibility of Results; D012588:Scintillation Counting / Q000379:methods*; D012825:Silicon / Q000737:chemistry*
chemical_list: D012825:Silicon