title: Effect of anode angle on photon beam spectra and depth dose characteristics for X-RAD320 orthovoltage unit.
abstract: BACKGROUND
  In radiation therapy with orthovoltage units, the tube design has a crucial effect on its dosimetric features.
  
  
  OBJECTIVE
  In this study, the effect of anode angle on photon beam spectra, depth dose and photon fluence per initial electron was studied for a commercial orthovoltage unit of X-RAD320 biological irradiator.
  
  
  METHODS
  The MCNPX MC code was used for modeling in the current study. We used the Monte Carlo method to model the X-RAD320 X-ray unit based on the manufacturer provided information. The MC model was validated by comparing the MC calculated photon beam spectra with the results of SpekCalc software. The photon beam spectra were calculated for anode angles from 15 to 35 degrees. We also calculated the percentage depth doses for some angles to verify the impact of anode angle on depth dose. Additionally, the heel effect and its relation with anode angle were studied for X-RAD320 irradiator.
  
  
  RESULTS
  Our results showed that the photon beam spectra and their mean energy are changed significantly with anode angle and the optimum anode angle of 30 degrees was selected based on less heel effect and appropriate depth dose and photon fluence per initial electron.
  
  
  CONCLUSIONS
  It can be concluded that the anode angle of 30 degrees for X-RAD320 unit used by manufacturer has been selected properly considering the heel effect and dosimetric properties.
authors.affiliation: Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran ; Radiation Oncology Department, Imam Hospital, Tabriz, Iran.
authors.forename: Asghar
authors.initials: A
authors.lastname: Mesbahi
authors.affiliation: Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Seyed-Salman
authors.initials: SS
authors.lastname: Zakariaee
keywords: Anode angle effect; Monte Carlo modeling; Radiation therapy; X-RAD320 irradiator