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

• Published in: Medical & biological engineering & computing 2015-01, Vol.53 (1), p.67-75
• Main Authors: Ezzati, A. O., Xiao, Y., Sohrabpour, M., Studenski, M. T.
• Format: Article
• Language: English
• Subjects: Animals; Atoms & subatomic particles; Biomedical and Life Sciences; Biomedical Engineering and Bioengineering; Biomedicine; Charged particles; Cobalt; Codes; Computer Applications; Computer Simulation; Damage; Deoxyribonucleic acid; DNA Damage; Dose-Response Relationship, Radiation; Dosimetry; Drug dosages; Electrons; Energy; Energy spectra; Human Physiology; Imaging; Mathematical analysis; Monte Carlo Method; Monte Carlo methods; Monte Carlo simulation; Oncology; Original Article; Particle Accelerators; Photon beams; Photons; Radiation therapy; Radiology; Relative Biological Effectiveness; Spectra; Spectrum analysis; Studies; Thermodynamics
• ISSN: 0140-0118; 1741-0444
• DOI: 10.1007/s11517-014-1213-3

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 cm 2 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 20 keV.