Calculation ofthe Inactivation Cross Section of V79 Cells by Protons in Radiotherapy

Objective: for efficient applications of protons in radiotherapy, detailed knowledge of the corresponding radiobiological mechanismis necessary. the inactivation cross section is a useful tool to explore the interaction mechanism. hence, the inactivation cross sectionfor proton irradiation on v79 cells has been calculated using published survival data. method: the linear quadratic equation was usedto fit the survival curves and the parametero was use d to calculate the cross section . the cross section a is plotted as a function of themean free path lambda and the linear energy transfer let. results: the cross section alfa-versus-lambda curve shows a saturation region between lambda> = 2 nm and lambda< =5 nm. in this region, the inactivation cross section value is about the same as the geometrical area of the dna segment ( ~ 4 mo m square 2 ). such a saturation is also seen in the delta -let curve. conclusion: this implies that one dna segment is at a risk upon the traversal of a single proton .