Proceedings to the 58th Annual Conference of the Particle Therapy Cooperative Group (PTCOG58)

The reference dosimetry in hadron therapy is based in the detection of secondary electrons generated by the ionization ofthe gas contained in ionization chambers. To determine the dose in liquid water, conversion factors such as W-values (meanenergy expended by the incident particle to form an electron-hole pair after complete dissipation of its initial energy) in the gasof the ionization chamber are necessary. This physical parameter represents an important source of uncertainties in hadrontherapy [1]. In a recent work [2] we studied the W-values by electron, proton and antiproton impact on vapor and liquid water.We used two different methods to take into account the slowing down of the primary particle and all the secondary electronsgenerated: the Monte Carlo code MDM (which does an event-by-event tracking of all particles, the primary and the secondaryelectrons) and the Fowler Equation (based in the Continuous Slowing Down Approximation). The results are in very goodagreement with experimental data for water vapor and with values obtained by other authors for liquid water. In the presentwork, we calculate W-values by proton impact on the gases that compose the air extending the theoretical methods developedin [2]. Results obtained for proton energies from 0.5 to 100 MeV are in very good agreement with experimental data. In futurework, these models will be extended to calculate W-values for other ions used in hadron therapy