The effect of energy spectrum change on DNA damage in and out of field in 10-MV clinical photon beams

A. O. Ezzati, Y. Xiao, M. Sohrabpour, M. T. Studenski

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The aim of this study was to quantify the DNA damage induced in a clinical megavoltage photon beam at various depths in and out of the field. MCNPX was used to simulate 10 × 10 and 20 × 20 cm2 10-MV photon beams from a clinical linear accelerator. Photon and electron spectra were collected in a water phantom at depths of 2.5, 12.5 and 22.5 cm on the central axis and at off-axis points out to 10 cm. These spectra were used as an input to a validated microdosimetric Monte Carlo code, MCDS, to calculate the RBE of induced DSB in DNA at points in and out of the primary radiation field at three depths. There was an observable difference in the energy spectra for photons and electrons for points in the primary radiation field and those points out of field. In the out-of-field region, the mean energy for the photon and electron spectra decreased by a factor of about six and three from the in-field mean energy, respectively. Despite the differences in spectra and mean energy, the change in RBE was <1 % from the in-field region to the out-of-field region at any depth. There was no significant change in RBE regardless of the location in the phantom. Although there are differences in both the photon and electron spectra, these changes do not correlate with a change in RBE in a clinical MV photon beam as the electron spectra are dominated by electrons with energies >20 keV.

Original languageEnglish (US)
Pages (from-to)67-75
Number of pages9
JournalMedical and Biological Engineering and Computing
Issue number1
StatePublished - Jan 2015


  • DNA damage
  • Monte Carlo
  • Radiotherapy
  • Spectrum analysis

ASJC Scopus subject areas

  • Biomedical Engineering
  • Computer Science Applications


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