Effect of backscatter on cell survival for a clinical electron beam.

Relative to homogeneous scattering conditions in tissue-like materials, a large increase in dose for clinical electron beams can occur upstream from high atomic number heterogeneities due to backscattered electrons. The degree of this dose increase is uncertain due to the unknown energy distribution of the backscattered electron fluence. Cell survival after irradiation was studied for Chinese hamster cells at the depth of maximum dose in a clinical 6 MeV electron beam under normal scattering conditions and with the addition of a lead backscatter. No significant difference in cell survival was found between the two geometries when the dose increase due to the backscattered electron fluence was approximated by the product of the measured ionization and the normal scattering stopping power ratio.