title: Calculation of the inactivation cross section of v79 cells by protons in radiotherapy.
abstract: OBJECTIVE
  For efficient applications of protons in radiotherapy, detailed knowledge of the corresponding radiobiological mechanism is necessary. The inactivation cross section is a useful tool to explore the interaction mechanism. Hence, the inactivation cross section for proton irradiation on V79 cells has been calculated using published survival data.
  
  
  METHODS
  The linear quadratic equation was used to fit the survival curves and the parameter α was used to calculate the cross section. The cross section σ is plotted as a function of the mean free path λ and the linear energy transfer LET.
  
  
  RESULTS
  The cross section σ-versus-λ curve shows a saturation region between λ≥2 nm and λ≤5 nm. In this region, the inactivation cross section value is about the same as the geometrical area of the DNA segment (≈4 μm(2)). Such a saturation is also seen in the σ-LET curve.
  
  
  CONCLUSIONS
  This implies that one DNA segment is at a risk upon the traversal of a single proton.
authors: Department of Physics, College of Education, University of Mosul, Iraq.
authors: Faika A
authors: FA
authors: Azooz
authors: Thamer J
authors: TJ
authors: Alkhalidy